Home Page Link AgBioWorld Home Page
About AgBioWorld Donations Ag-Biotech News Declaration Supporting Agricultural Biotechnology Ag-biotech Info Experts on Agricultural Biotechnology Contact Links Subscribe to AgBioView Home Page

AgBioView Archives

A daily collection of news and commentaries on
ag-biotech.


Subscribe AgBioView Subscribe

Search AgBioWorld Search

AgBioView Archives

Subscribe

 


SEARCH:     

Date:

April 14, 2001

Subject:

Examining Biotech and Breeding to Improve Food Nutrient

 

The Role of Biotechnology for Food Consumers In Developing Countries

Howarth E. Bouis
International Food Policy Research Institute, Washington, DC

(This paper examines various strategies such as plant breeding and
biotechnology to improve micro-nutrient content of food crops including
the beta-carotene as with Golden Rice... for more information and to get
a copy of the original pdf file of this paper write to author at
... reproduced with permission of the author... CSP)

Published In: Agricultural Biotechnology in Developing Countries: Towards
Optimizing the Benefits for the Poor; Qaim, M., A. Krattiger, and J. von
Braun (eds.); Kluwer Academic Publishers, Chapter 11

Abstract
This paper assesses the potential benefits that biotechnology can provide
food consumers in developing countries by examining the recent history of
attempts to improve the micronutrient content of food crops, efforts that
have used both biotechnology and traditional plant breeding. In developing
countries, micronutrient deficiencies affect many of the poor, whose diets
consist mostly of staple foods. Breeding to enhance the micronutrient
levels in staple foods could help reduce this problem. Since trace
minerals are also important for plant nutrition, related breeding may
increase farm productivity at the same time. Plant breeding is more
efficient than alternative interventions already in place for reducing
micronutrient malnutrition. Identifying the appropriate combination of
traditional and biotechnology tools should be based on cost-effectiveness
considerations. The potentially enormous benefits to the poor in
developing countries in relation to costs are so high that research in
this area should be vigorously pursued.

1 INTRODUCTION
In order to assess the potential benefit of biotechnology for food
consumers in developing countries, this paper examines the recent history
of attempts to improve the micronutrient content of staple foods, efforts
that have used both biotechnology and traditional plant breeding. This
concrete example will serve to illustrate several key generic issues
associated with using biotechnology to breed for characteristics that
benefit consumers. Biotechnology can, of course, be used to help solve a
number of problems, but its potential usefulness depends on the context of
a particular problem. It will be necessary, therefore, to discuss in some
detail the context of breeding for improved micronutrient density.

Taken together, mineral and vitamin deficiencies affect a greater number
of people in developing countries than protein-energy malnutrition.
Because trace minerals are important not only for human nutrition but also
for plant nutrition, plant breeding has great promise for making a
significant, low-cost, sustainable contribution to reducing micronutrient
deficiencies, particularly mineral deficiencies. It may also have
important spin-off effects for environmentally beneficial increases in
farm productivity for developing countries (Cary et al., 1994; Welch et
al., 1993; Kannenberg and Falk, 1995; Graham and Welch, 1996; Graham et
al., 1999).

The following section briefly summarizes the extent and consequences of
micronutrient malnutrition in developing countries, as well as the
effectiveness of the non-agricultural interventions currently being used
to address this problem. We then argue that plant breeding is a low-cost,
sustainable intervention that can substantially reduce micronutrient
malnutrition. This is a new, perhaps not yet widely accepted strategy for
addressing this enormous problem, whether using biotechnology or
conventional breeding techniques. The progress of such a strategy using
conventional breeding techniques is then reported, focusing on rice.
Recent advances using biotechnology to improve the micronutrient content
of rice are also presented, which permits a discussion of the ways in
which conventional and biotechnology approaches are complementary and of
what biotechnology can accomplish that conventional breeding cannot.
Finally, we draw some general lessons for assessing the potential of
biotechnology to improve human nutrition.

2 MICRONUTRIENT MALNUTRITION: EXTENT, COSTS, ALTERNATIVE INTERVENTIONS
Only relatively recently have nutritionists working in developing
countries been able to demonstrate that many children and adults,
particularly women in their childbearing years, suffer more from a lack of
essential vitamins and minerals in their diets than from a lack of
calories — even during relative economic and political stability. People
are unaware that their diets lack these trace nutrients, and they do not
associate these deficiencies with listlessness, poor eyesight, impaired
cognitive development and physical growth, and more severe bouts of
illness (sometimes leading to death). Accordingly, this general problem of
poor dietary quality has been dubbed “hidden hunger”. In an observational
study, researchers from Johns Hopkins University working in Indonesia
showed a correlation between progressively serious eye damage in children
and increased child mortality rates. This empirical information was
consistent with a long suspected link between vitamin A deficiency and the
high child mortality rates common in developing countries. To test this
hypothesis more rigorously, 10,000 Indonesian children were given
high-dose vitamin A capsules (VAC) and 10,000 children were given a
placebo (a low percentage of these children, no more than one percent, had
clinically visible eye damage). Mortality rates were found to be 34
percent lower for children who received VAC.

Such a large reduction in mortality was so startling and unexpected that
eventually it was necessary to conduct seven similar experiments in Africa
and Asia (with similar results on average) before it was widely accepted
by the international nutrition community (in the late 1980s) that
widespread distribution of VAC could significantly reduce child mortality
and should be made a high priority for government intervention. These
dramatic, new research findings in the area of vitamin A deficiency also
helped to focus more attention and spur further research related to other
micronutrient deficiencies, in particular iron and iodine deficiencies.

The World Health Organization (WHO) now compiles statistics on a regular
basis about the extent of micronutrient deficiencies and this has revealed
the enormous magnitude of the problem. WHO reported in 1994 that 3 million
pre-school age children had eye damage due to a vitamin A deficiency and
another 200 million are sub-clinically affected at a severe or moderate
level. Annually, an estimated 250,000-500,000 pre-school children go blind
from this deficiency, and about two-thirds of these children die within
months of going blind. Globally, over three billion people are
iron-deficient (ACC/SCN, 2000). The problem for women and children is more
severe because of their greater physiological need for iron. In developing
countries, more than 40 percent of non-pregnant women and pre-school
children and more than one-half of pregnant women have anemia. Of the
approximately 500,000 maternal deaths that occur each year due to
childbirth, mostly in developing countries, anemia is the major
contributor or sole cause in 20-40 percent of such deaths. Iron
deficiencies during childhood and adolescence impair physical growth,
mental development and learning capacity. In adults, iron deficiency
reduces the capacity to do physical labor.

Deficiencies in several other micronutrients, zinc in particular, may be
similarly widespread with equally serious consequences for health (Gibson,
1994). However, because there are no specific indicators to screen for
zinc deficiencies (other than a positive health response to
supplementation), zinc has not received as much attention. The costs
involved in fortification and supplementation are considerable. The
recurrent, annual, lower-bound estimate for iron supplementation is US
$2.65 per person when administrative costs are taken into account (Levin
et al., 1993). A lower-bound estimate for iron fortification is 10 cents
per person per year. In a populous country such as India (total population
1 billion) there may be as many as 28 million anemic pregnant women in any
given year. Treating only half of those women through a well-targeted
supplementation program could cost as much as US $37 million per year.
Iron fortification for half the entire population could cost $44 million
per year. Notwithstanding these cost estimates, the benefits of properly
managed interventions can be quite significant.

The World Bank’s World Development Report 1993 found that micronutrient
programs were among the most cost-effective of all health interventions. A
World Bank document (1994) estimates that deficiencies of just vitamin A,
iodine, and iron alone could waste as much as 5 percent of gross domestic
product (GDP) in developing countries, but addressing them comprehensively
and sustainably would cost less than one-third of a percent of GDP.
Nevertheless, it is difficult for governments and international agencies
to mobilize resources of this magnitude.

Although successful supplementation and fortification do not require a
substantial change in individual behavior, these interventions only treat
the symptoms and not the underlying causes of micronutrient deficiencies.
This has led many to advocate the use of “food-based” interventions, such
as nutrition education and the promotion of home vegetable gardens, that
address the underlying cause of poor quality diets and also provide a
range of other important nutrients. This approach, however, means changing
human behavior, which can be both expensive and difficult. New and
compelling scientific evidence is rapidly accumulating to support the
claim that nutrition and health in developing countries can be
dramatically improved by reducing micronutrient malnutrition. It is an
enormous opportunity. Nevertheless, there is some frustration at the lack
of appropriate, well-developed tools for developing countries to solve the
problem of micronutrient deficiencies quickly and at a reasonable cost.

3 CAN A PLANT BREEDING STRATEGY WORK? FIVE KEY QUESTIONS
A strategy of breeding plants that enrich themselves and load high amounts
of minerals and vitamins into their edible parts has the potential to
substantially reduce the recurrent costs associated with fortification and
supplementation. But this will be successful only if farmers are willing
to adopt such varieties, if the edible parts of these varieties are
palatable and acceptable to consumers, and if the incorporated
micronutrients can be absorbed by the human body. Indeed, five core
questions must be addressed to examine the feasibility of such a plant
breeding strategy.

3.1 Is it Scientifically Feasible to Breed Micronutrient-Dense Staple Food
Varieties? : At least three agricultural research projects in developed
countries have successfully manipulated the mineral uptake of plants and
the mineral content of plant seeds, and all these projects have been
commercially successful. Zinc-dense wheat varieties, developed at the
Waite Agricultural Research Institute of the University of Adelaide, are
already being grown on a commercial basis in Australia (Rengel and Graham,
1995). In the United States, an iron-efficient soybean has been developed
to overcome problems of iron “deficient” soils, and cadmium levels in
durum wheats have been reduced through plant breeding to meet quality
standards in countries importing US wheat.

3.2 What are the Effects on Plant Yields? Will Farmers Adopt Such
Varieties? : Results from research at Waite and elsewhere has shown that
where the soil is deficient in a particular micronutrient, seeds
containing more of that nutrient have better germination, better seedling
vigor and/or more resistance to infection during the vulnerable seedling
stage (Pearson and Rengel, 1995; McCay et al., 1995). Since these crop
establishment benefits can result in higher crop yield, the specific
breeding goals for human and plant nutrition largely coincide. A soil is
said to be “deficient” in a nutrient when the addition of a fertilizer
containing that nutrient produces better growth. But the amount of the
mineral micronutrient that is added to the soil to improve growth is
usually small compared to the total amount of that mineral found in the
soil. Because the trace mineral is chemically bound to other elements in
the soil, the major part of the trace mineral is “unavailable” to plants.
An alternative view, therefore, is that instead of soil deficiency there
is a genetic deficiency in the plant. Tolerance to micronutrient-deficient
soils, termed micronutrient efficiency, is a genetic trait of a genotype
or phenotype that causes a plant to be better adapted or to produce higher
yields in a micronutrient-deficient soil than the average cultivar of the
species (Graham and Rovira, 1984). Growing zinc-efficient plants on
zinc-deficient soils, for example, “tailors the plant to fit the soil”
instead of “tailoring the soil to fit the plant” (Foy, 1983). These
efficient genotypes exude substances from their roots that chemically
unbind trace minerals from other binding elements and make trace minerals
available to the plant.

It is well understood that without replacement the depletion of soil
nitrogen takes only a few years. Consequently, it is pointless to breed
for greater tolerance to nitrogen-deficient soils. Phosphorus efficiency
results in overall improvements in cost-efficiency but, without
replenishment, depletion of soil phosphorous will also eventually occur.
In contrast, the depletion of mineral micronutrients may take hundreds or
thousands of years – or may likely never occur at all – due to various
inadvertent additions and other processes, such as minerals carried in
windblown dust (Graham, 1991). Based on a number of soil surveys,
particularly in China where the most extensive surveys have been done, it
is estimated that at least 50 percent of the arable land used for crop
production worldwide is low in one or more of the essential
micronutrients. For example, although iron is the fifth most abundant
element in the earth’s crust, the fraction of soil iron that is in soluble
form for absorption by plants may only be 10 -13 of total soil iron.

Depletion of soil iron is never an issue; instead, the issue is the
ability of the plant to mobilize sufficient iron to satisfy its needs (Han
et al., 1994). Zinc deficiency is probably the most widespread
micronutrient deficiency in cereals. Sillanpaa (1990) found that 49
percent of a global sample of 190 soils in 25 countries were low in zinc.
Unlike other micronutrients, zinc deficiency is a common feature of both
cold and warm climates, in soils drained and flooded, acid and alkaline,
heavy and light (Rahman et al., 1993).

Good nutrition balance is as important for disease resistance in plants as
it is in humans. The efficient uptake of mineral micronutrients from the
soil is associated with disease resistance in plants, which leads to
decreased use of fungicides. Micronutrient deficiency in plants greatly
increases their susceptibility to diseases, especially fungal root
diseases of the major food crops. The picture emerging from four decades
of physiological studies of roots is that phosphorus, zinc, boron, calcium
and manganese are all required in the external environment of the root for
membrane function and cell integrity. In particular, phosphorus and zinc
deficiencies in the external environment promote the leaking of cell
contents such as sugars, amides and amino acids. These substances are
chematoxic stimuli to pathogenic organisms. It also appears that
micronutrient deficiency predisposes the plant to infection, rather than
the infection causing the deficiency through its effect on root pruning
(Sparrow and Graham, 1988; Thongbai et al., 1993). Breeding for
micronutrient efficiency can also confer resistance to root diseases that
had previously not been amenable to breeding solutions. This could mean a
lower dependence on fungicides. Micronutrient-efficient varieties grow
deeper roots in mineral deficient soils and are better at tapping subsoil
water and minerals (Grubb, 1994; Brown et al., 1994). When topsoil dries,
roots in the dry soil zone (which are not tightly linked to agronomic zinc
efficiency traits and may have to be selected for independently.

3.3 Will Micronutrient-Density: Change the Consumer Characteristics?
Mineral micronutrients comprise a tiny fraction of the physical mass of a
seed, perhaps ten parts per million. Dense seeds may contain perhaps as
many as fifty parts per million. It is not expected that such small
amounts will alter the appearance, taste, texture or cooking quality of
foods. Increasing the seed content of beta-carotene, which is associated
with an orange or yellow color, will alter its color. This might well
reduce consumer preference, but nutrition education could turn this
obstacle to an advantage, as consumers could be taught that deepness of
color indicates a nutrient-dense product.

3.4 Will the Extra Micronutrients in Staple Foods be Bioavailable?: An
underlying cause and fundamental constraint to solving the micronutrient
malnutrition problem is that non-staple foods, particularly animal
products, tend to be the foods richest in bioavailable micronutrients.
These are precisely the foods that the poor in developing countries cannot
afford. Their diets consist mostly of staple foods, primarily cereals. For
the poor, these staple foods already are primary sources of what
micronutrients they are able to consume, particularly minerals. This is
demonstrated by food intake data shown in Table 1 for survey populations
in Bangladesh and the Philippines. Average incomes in these households
range from US $45 per capita per year in the poorest 20 percent of
households to $250 in the richest 20 percent of households. Thus, they are
typical of the middle to lower end of the income distribution in the rural
areas of these countries. The first priority for these poor households in
terms of food purchases is to obtain calories to satiate hunger. The most
inexpensive sources of calories in Bangladesh are rice and wheat; in the
Philippines they are maize and rice. Once a critical amount of calories
are acquired from inexpensive food staples, if income is available,
consumers purchase non-staple foods at the margin, particularly animal
products and fruits, and to some extent substitute more expensive, more
preferred food staples for inexpensive staples. Not only are food staples
poor (non-dense) sources of trace minerals, but anti-nutrient (e.g.,
phytic acid) levels are high, which reduces the overall human health.
Therefore, they argue against a breeding strategy that attempts to
increase iron bioavailability by reducing anti-nutrient content. Raboy
(1996), however, has developed low phytic acid (or lpa) mutant varieties
of maize, rice and barley. The phytic acid content of lpa seeds is reduced
by 50-80 percent as compared with non-mutant seeds. The total amount of
phosphorus remains the same – phytic acid is replaced by inorganic
phosphorus, which does not bind a range of trace minerals.

These mutations typically have little observable effect on other seed or
plant characteristics. These varieties are presently being tested for
agronomic performance and effects on micronutrient status in humans.
Promoters of bioavailability. Certain amino acids (cysteine and lysine,
but particularly methionine) enhance iron and/or zinc bioavailability
(Hallberg, 1981). These amino acids occur in many staple foods, but their
concentrations are lower than those found in meat products. A modest
increase in the concentrations of these amino acids in plant foods may
have a positive effect on iron and zinc bioavailability in humans. Iron
and zinc occur only in micromolar amounts in plant foods, so only
micromolar increases in the amounts of these amino acids may be required
to compensate for the negative effects of anti-nutrients on iron and zinc
bioavailability. These amino acids are essential nutrients for plants as
well as for humans, so relatively small increases of their concentrations
in plant tissues should not have adverse consequences on plant growth .
---
Table 1: (unable to reproduce the table!!)
-----
Nevertheless, Table 1 reveals that primary food staples provide about
40-55 percent of total iron intakes for lower income households. If a
single food staple provides 50 percent of total iron intakes for a poor
population (e.g., rice in Bangladesh), then a doubling of the iron density
in that food staple will increase total iron intakes by 50 percent, and
tripling the iron density will double total iron intakes. One strength of
a plant breeding approach that focuses on food staples, therefore, is that
it relies on existing consumer behavior. The poor consume large amounts of
food staples on a daily basis. If a high proportion of the domestic
production of food staples can be provided by nutritionally improved
varieties, nutritional status can be improved without resorting to
programs that depend on behavioral change.

A key issue is whether the bioavailability percentage of total iron (or
zinc) intakes will remain constant or decline. Rat studies suggest that
the percent of bioavailable iron (and zinc) remains relatively constant
across cereal genotypes with high and low density (Welch, 1996; Welch et
al., 1 Likewise, if nutritionally-improved varieties have unique agronomic
advantages in trace mineral-deficient soils, or if these traits are
incorporated into highly profitable varieties, then no behavioral change
is required of farmers since profits will motivate them to adopt and
produce these nutritionally-improved varieties.

3.5 Are there Cheaper or Easier Sustainable Strategies for Reducing
Micronutrient Malnutrition?
A plant breeding strategy, if successful, will not eliminate the need for
supplementation, fortification and dietary diversification programs in the
future. Nevertheless, by significantly reducing the numbers of people
requiring treatment, this strategy has the promise to significantly reduce
the recurrent expenditures required for these higher-cost, short-run
programs. Costs of plant breeding. To obtain a rough estimate of plant
breeding costs, the example of the CGIAR Micronutrients Project may be
used. This project is a multi-disciplinary effort among plant scientists,
human nutritionists and social scientists. The general objective over five
years is to assemble the package of tools that plant breeders will need to
produce mineral- and vitamin-dense cultivars. The target crops are wheat,
rice, maize, phaseolus beans and cassava. The target micronutrients being
studied 2 When such mutants are used as animal feeds, this also avoids
what has become a serious pollution problem: excretion of unutilized
phytic acid. (??) are iron, zinc and vitamin A. The plant breeding effort
can be seen as a two-stage process. The first five-year phase primarily
involves research at central agriculture research stations, at an
estimated US $2 million per year for research on all five crops. During
this initial phase, promising germplasm is identified and the general
breeding techniques are developed for later adaptive breeding. During the
second phase, the emphasis shifts to national agricultural research. Total
costs and duration of this second phase are difficult to estimate, but
will depend on the number of countries involved and the number of crops
worked on in each country. The annual cost for each country should not be
more than the US $2 million per year estimated for the first phase.

Benefits to improved human nutrition:. The World Bank (1994) estimates
that at the levels of micronutrient malnutrition existing in South Asia, 5
percent of gross national product is lost each year due to deficiencies in
the intakes of just three nutrients: iron, vitamin A and iodine. For a
hypothetical country of 50 million persons burdened with this rate of
malnutrition, deficiencies in these three nutrients could be eliminated
through fortification programs costing a total of US $25 million annually,
or 50 cents per person per year. The monetary benefit to this $25 million
investment is quite high in terms of increased productivity – estimated at
$20 per person per year, or a forty-fold return on an investment of 50
cents. These benchmark numbers will be used below as a basis of comparison
with the benefits of a plant breeding strategy.

Calculation of benefit-cost ratios: The details of a formal benefit-cost
analysis are presented in Bouis (1999). Expressed in present values, costs
are about US $13 million and benefits $274 million, giving a benefit-cost
ratio of over 20, which is quite favorable despite the very conservative
assumptions made and despite the long time lag between investments and
benefits. This last point highlights an essential difference between
investments in standard fortification programs and fortification through
plant breeding strategies. Standard fortification programs must be
sustained at the same level of funding year after year. If investments are
not sustained, benefits disappear. Such investments apply to a single
geographical area, such as a nation-state. By contrast, research
investments in plant breeding have multiplicative benefits that may accrue
to a number of countries. Moreover, these benefits are sustainable, since
as long as an effective domestic agricultural research infrastructure is
maintained, breeding advances typically do not disappear after initial
investments.

4 FINDINGS-TO-DATE OF THE CGIAR MICRONUTRIENTS PROJECT
Convinced that the existing scientific evidence provided satisfactory
answers to the above five questions, since 1995 the Danish Development
Agency (DANIDA), the US Agency for International Development (USAID), and
the Australian Council for International Agricultural Research (ACIAR)
have funded exploration of the potential for micronutrient density in
CGIAR germplasm banks of the major staple crops. A report was published
recently for several food staples (Graham et al., 1999). A summary of
these findings with respect to rice is presented below. Rice. The findings
in the rice component of the project are particularly encouraging. Iron
density in unmilled rice varied from 7-24 parts per million (ppm or mg/kg)
and zinc density from 16-58 ppm. Because nearly all the widely grown
“green revolution“ varieties were similar, a benchmark was established of
about 12 and 22 ppm for iron and zinc, respectively. The best lines
discovered in the survey of the germplasm collection were therefore twice
as high in iron and 1.5 times as high in zinc as the most widely grown
varieties today. High iron and to a lesser extent, high zinc
concentration, were subsequently shown to be linked to the trait of
aromaticity. Most aromatic rices, such as jasmine and basmati, are high in
iron, zinc and generally in most minerals (Senadhira and Graham, 1999;
Graham et al., 1997; Graham et al., 1999). The close linkage to aroma
suggests iron density in rice expresses as a single gene trait since aroma
is itself controlled at a single locus.

As in other crops, these micronutrient density traits have been combined
with high yield. A promising aromatic variety found to be high in iron,
designated IR68-144, is already being tested at IRRI due to its superior
agronomic and consumer characteristics. This aromatic variety has double
the iron (after milling) of standard IRRI releases and is early maturing,
high yielding and disease resistant. Bioavailability tests using human
subjects are planned to begin in 2000. Pending the results of these
bioavailability tests and agronomic tests to be undertaken by the
Philippine Seed Board, IR68- 144 may be ready for release to farmers in
the Philippines in a few years. Genotype environment interactions.
Expression of the micronutrient-density traits has been tested over a wide
range of environments, and although the environmental effect itself is
strong, the genotype effect is consistent across environments and
sufficient to encourage a breeding effort. Environmental factors
considered by one or more of the crop programs include acid soils,
alkaline soils, saline soils, acid-sulfate soils, iron-deficient soils,
time of planting, field site, season, nitrogen fertilization, phosphorus
fertilization, potassium status, elevation and drought stress.

5 RECENT FINDINGS ON IMPROVING THE NUTRIENT CONTENT OF RICE USING
BIOTECHNOLOGY

5.1 Increasing Iron Content: Ferritin is an iron-storage protein found in
animals, plants and bacteria. The ferritin gene has been isolated and
sequenced in plants, including soybean, French bean, pea and maize. Recent
studies show that both plants and animals use ferritin as the storage form
of iron and that, orally administered, it can provide a source of iron for
treatment of rat anemia (Beard et al., 1996). However, human studies with
extrinsically radiolabeled animal ferritin have indicated that iron
contained within the ferritin molecule added to a meal is only about half
as well absorbed as vegetable iron (Martinez-Torres et al., 1976; Taylor
et al. 1986) and as ferrous sulphate (Skikne et al., 1997).

As yet, there have been no human studies with plant ferritin, and animal
studies are not considered a good model for humans (Hurrell, 1997). Goto
et al. (1999) report improving the iron content of rice by transferring
the entire coding sequence of the soybean ferritin gene into a Japonica
rice. The introduced ferritin gene was expressed under the control of a
rice seed-storage protein glutelin promoter to mediate the accumulation of
iron specifically in the grain. The transgenic seeds stored up to three
times more iron than the normal seeds. Iron levels in the unmilled seeds
of the transformants varied from 13 to 38 ppm, while that of the
non-transformants varied from only 9 to 14 ppm. Pooled mean values were 23
ppm for transformants and 11 ppm for non-transformants. The average iron
content in the endosperm of the transformant was 3.4 ppm and 1.6 ppm in
the non- 3 The authors state that the iron content in a meal-size portion
of ferritin rice (approximately 5.7 mg-Fe/150 g dryweight) would be
sufficient to provide 30-50 percent of the daily adult iron requirement.
5.7 mg-Fe is presumably obtained by multiplying 38 ppm by 150 g.
Unfortunately, this calculation assumes that consumers eat unmilled rice.
The iron added by the ferritin rice in the endosperm is 1.8 ppm (3.4 ppm
minus 1.6 ppm), which when multiplied by 150 g, gives only an extra 0.27
mg Fe per meal-sized portion. Nevertheless, this alternative calculation
probably understates the iron added because milling does away with much,
but not all of the seed’s brown outer covering (bran) that is relatively
dense in iron.

In a heavy rice-eating population, an adult may consume 400 g (1,400 kcal)
of rice (dryweight) a day. If the differential in iron content in milled
rice is 10 ppm between an iron-dense (say 18 ppm) and normal-iron rice
(say 8 ppm), this confers an additional 4 mg of iron to the diet per day,
which may be a 50 percent increase over the average daily intake of a poor
person who obtains 80-90 percent of their energy from rice. This
underscores the importance of determining where in endosperm the iron (and
other trace minerals) are deposited and how mineral levels are affected by
milling. (??) transformant. The authors speculate that the amount of iron
accumulation is restricted by the transport of iron to the ferritin
molecule, rather than simply by levels of ferritin protein. It may be
possible, therefore, to store larger amounts of iron in the ferritin
molecule by cointegrating the ferritin gene and the iron reductase-like
transporter gene.

Although results have yet to be published in a refereed journal, at a
recent conference Ingo Potrykus and colleagues at the Swiss Federal
Institute of Technology announced a doubling of the iron content in a rice
using a ferritin gene derived from Phaseolus vulgare (cf. Gura, 1999).
Metallothionine was also expressed in the rice grain, increasing the
cysteine content seven fold. It is not known if the cysteine containing
peptides formed on digestion of metallothionine in the human gut have a
similar enhancing effect on iron absorption as those formed on digestion
of muscle tissue (Hurrell, personal communication).

5.2 Introducing a Heat-Stable Phytase Gene Which Breaks Down Phytic Acid:
The phytase level in rice is normally low. Several studies have already
demonstrated the usefulness of adding phytase to the rice diets of poultry
(e.g., Adrizal et al., 1996; Farrell and Martin, 1998; Martin et al.,
1998). The phytase found in rice seeds will hydrolyze phytic acid if seeds
are soaked in water. However, boiling destroys the phytases that occur
naturally in rice. The research team led by Potrykus also reported
introducing a transgene for a heat-stable phytase from Aspergillus
fumigatus, which increased the level of phytase 130-fold. The fact that
the phytase is potentially heat-stable, then, is critically important. An
amino acid had been changed in the sequence to make the phytase heat
stable (Pasamontes, 1997). It was also active under the conditions (pH) of
digestion and degraded all the phytic acid in a very short time during
model in vitro digestion. Unfortunately, after expression in the grain it
was no longer stable to heat and lost its activity on boiling (Hurrell,
personal communication). 5.3 Increasing Promoters Levels of lysine, an
essential but limiting amino acid in rice that might promote the uptake of
trace minerals, can be increased by genetic engineering (Datta, 1999). The
introduction of two bacterial genes DHSPS (dihydrodipicolinic acid
sythase) and AK (aspartokinase) enzymes encoded by the Corynebacterium
dapA gene and a mutant E. coli lysC gene have enhanced lysine about
five-fold in canola and soybean seeds (Falco et al., 1995).

5.4 Adding Beta-Carotene: Beta-carotene, a precursor of vitamin A
(retinol), does not occur naturally in the endosperm of rice. Ye et al.
(2000) have reported generating a large series of transgenic plants that
produce grain with yellow-colored endosperm. Biochemical analysis
confirmed that the color represents beta-carotene (provitamin A).
According to Ye et al. (2000), psy (cloned from Narcissus pseudonarcissus;
Schledz et al., 1996), cryt1 (cloned from Erwinia uredovora; Misawa et
al., 1993), and the lyc gene have been introduced into the rice, driven by
the endosperm specific glutelin promoter (Gt1). Crt1 was fused to the
transit peptide (tp) sequence by the pea Rubisco small sub-unit (Misawa et
al., 1993) to lead the accumulation of lycopene in the endosperm plastids.
This is a remarkable accomplishment considering that most traits
engineered to date have only required the addition of a single gene
(Guerinot, 2000). The reported level of beta-carotene in one gram of the
transformed rice is 1.6 mg. Multiplying that by a daily intake of 400
grams of milled rice and dividing by a conversion ratio of 6 mg of
beta-carotene for every retinol equivalent (RE) gives 107 RE, which Ye et
al. (2000) state is the target level for improved nutrition. However,
widely accepted RDAs for vitamin A range between 375-1,200 RE depending on
age, gender and physiological status, and recent evidence suggests that
the conversion factor from beta-carotene to RE varies between 12-26 to 1
(de Pee et al., 1998). Nevertheless, RDAs are set relatively high by
adding two standard deviations to the observed mean requirements of a
nutrient for most people.

According to Datta (1999), the introduction of ferritin, heat-stable
phytase and beta-carotene in rice by the Potrykus-led team has been
accomplished individually in separate Japonica rices (i.e., not jointly in
the same rice). These cultivars may be used in the IRRI breeding program
to transfer the genes of interest to Indica cultivars from which IRRI
releases are derived. Alternatively, these genes can be introduced
directly into Indica cultivars using biotechnology. Ye et al. (2000) use a
ration of 300 g of milled rice in their calculations but add that they are
optimistic that they can reach a goal of 2 mg/g of beta-carotene in
homozygous lines. In a relatively heavy-rice-eating population such as
Bangladesh, non-breastfeeding pre-schoolers in rural areas might consume
250 g of milled rice per day (an RDA of 500 RE), adult women 500 g of
milled rice per day (an RDA of 800 RE if not pregnant or breastfeeding),
and adult men 650 g of milled rice per day (an RDA of 1,000 RE).

6 STRATEGY FOR COMBINING CONVENTIONAL BREEDING AND BIOTECHNOLOGY
What is the appropriate mix of conventional breeding techniques and
biotechnology in breeding for micronutrient-dense staple food crops? Where
are they complementary? Where is one approach feasible, but the other not?
Table 2 summarizes some of the issues involved. To return to two of the
themes raised earlier in the paper, the fundamental advantages of breeding
for increased trace minerals are that (i) agricultural productivity is not
compromised, indeed is enhanced on trace mineral deficient soils, and (ii)
consumer characteristics should remain unchanged. Thus, for rice, although
it is fortunate that IR68-144 was “discovered” without resort to breeding
explicitly for high iron, such a discovery has a relatively high
probability of occurring because of the compatibility with high yields of
the nutritional trait being sought. Such “discoveries” can greatly speed
up the development and dissemination process and lower the cost of
breeding. After milling, IR68-144 confers perhaps an 80 percent increase
in iron density over modern varieties presently being released. This is
about the same average advantage as reported by Goto et al. (1999) and the
Potrykus group. It may be possible to further elevate this 80 percent
advantage by crossing various iron-dense genotypes that may have
complementary, additive mechanisms for loading more iron into the seed.
The two successes at adding a ferritin gene to rice reported here have not
given superior results to those obtained by conventional plant breeding.
Moreover, breeding is still required to move the “ferritin” trait from
Japonica to high-yielding Indica rice varieties. It may be that eventually
the most iron-dense genotypes can be developed using biotechnology,
especially after the basic physiology of what mechanisms control
translocation of trace minerals in plants is better understood. However, a
specific strategy for doing so has yet to be demonstrated.

Goto et al. (1999) and Potrykus measure their iron increases against
benchmarks that are the non-transformed genotypes. But are these
benchmarks relatively high or low density genotypes to start with? The
only figures available are from Goto et al. (1999). Their maximum value of
38 ppm in brown rice is quite high compared with all rices analyzed under
the CGIAR Micronutrients Project. However, this was an analysis of only
one single grain from a plant grown under laboratory conditions (iron
content varies by weather and soil type). Analyses under the CGIAR
Micronutrient Project are averages for randomly drawn samples of several
seeds of a single genotype grown in a specific season on a specific soil.
Thus, the average of 23 ppm obtained by Goto et al. (only 11 grains in
total) is probably the best comparison with IR68-144, which has an iron
density of 23 ppm for some plantings (Gregorio, 1999).

====== Table 2: (not reproduced) =====

We conclude that, in the short-to-medium term, conventional breeding
methods may give superior results with respect to iron and zinc density as
compared to biotechnology. However, the implication is not that
biotechnology-related, long-term research to increase trace mineral
density should be stopped. Rather, spending using either methodology is
presently quite low and should be increased in view of the cost-benefit
analysis presented earlier.

Three complementary or alternative approaches to increasing the
bioavailability of trace minerals in the grains of food staples are listed
in Table 2: (i) reducing phytic acid, (ii) introducing phytase, and (iii)
increasing promoting compounds.

As described earlier, low phytic acid mutants of rice, maize, wheat and
barley have already been produced in which virtually all or a large
portion of the phytic acid has been replaced by inorganic phosphorus. This
is a promising approach in terms of improving human nutrition, although a
drawback may be its agronomic performance on phosphorus-poor soils.
Evidence about which compounds promote bioavailability, such as
sulfur-containing amino acids, is sketchy. Until this approach is more
thoroughly researched and specific compounds firmly identified as
promoting bioavailability, it is probably too early to begin breeding for
such compounds using conventional plant breeding or biotechnology. A
promising approach for the use of biotechnology with respect to trace
minerals is to add a heat-stable phytase to rice. This particular approach
is not an option for conventional plant breeding and can only be pursued
using biotechnology. No data exist on how adding phytase to rice would
affect agronomic performance or consumer characteristics. Turning now to
vitamins, the addition of beta-carotene in rice is possible only through
biotechnology. No rice has been identified with beta-carotene in the
endosperm.

Thus, the apparent success of Potrykus’ group in this regard is quite
exciting. Nevertheless, apart from breeding these beta-carotene- related
genes into high-yielding varieties and assessing possible effects on plant
productivity, it is already known that the beta-carotene turns the seeds
yellow. How willingly will poor consumers purchase and consume yellow
rice? Most people agree that without a complementary nutrition education
program, consumers will not readily accept “yellow rice.” Opinions differ
as to the power of nutrition education to overcome culturally held
preferences for white rice. It is easy to speculate either way, but no
hard data are available. If a nutrition education program were successful,
however, the yellow color would distinguish more nutritious rice from less
nutritious rice and the disadvantage of the yellow color would be turned
to an advantage.

An additional exciting possibility is that higher intakes of beta-carotene
(converted to retinol after ingestion) may promote absorption of iron and
vice versa. That is, there are possible synergies between higher intakes
of these two nutrients (Garcia-Casal et al., 1998). There is already
considerable evidence about the synergies between vitamin A and zinc
intakes (Smith, 1996). 6 According to Preben Holm (personal
communication), plant phytases have been very difficult to isolate. For
cereals there are only two maize phytase genes isolated, one expressed in
the seedling and the other in the root. This implies that there are
virtually no tools available for gene expression analyses and for immuno
detection of proteins.

7 LESSONS TO BE DRAWN
The following lessons may be drawn concerning the potential usefulness of
biotechnology in helping to provide more nutritious food staples in
developing countries:

1. It must be established that plant breeding is more cost-effective than
alternative interventions already in place to reduce micronutrient
malnutrition. This is apparently the case, in large measure because of the
multiplier effects of plant breeding – a relatively small, fixed, initial
investment in research may benefit the health of millions of poor people
in developing countries all over the world, at the same time improving
agricultural productivity on lands which are presently among the least
productive.

2. There must be aspects of the breeding strategy for which biotechnology
is superior to conventional breeding techniques. For rice, this is the
case for adding beta-carotene-related and heat-stable phytase genes. In
the long run, as more is understood about the factors driving
translocation of minerals in plants, it may also be helpful for increasing
trace mineral density. However, present evidence suggests that in the
short-run, conventional breeding techniques work as well and may be
applied more quickly.

3. In those areas of plant breeding where biotechnology is superior to
conventional plant breeding, it must be established that: (i) there are no
serious, negative agronomic consequences associated with the
characteristic being added; (ii) consumers will accept any noticeable
changes in the color, taste, texture, cooking qualities and other features
associated with the characteristic being added; and (iii) the
characteristic being added will measurably improve the nutritional status
of the malnourished target population. The conditions under lesson three,
in particular, have yet to be firmly established, but it is important not
to be overly cautious. The potentially enormous benefits to the poor in
developing countries in relation to costs are so high that research in
this area should be vigorously pursued.

8 CONCLUSION
Biotechnology can improve consumer welfare in a number of ways not
discussed in this paper. By helping to improve crop and animal
productivity and thereby increasing the growth rate of supply of a range
of foods, biotechnology can help reduce food prices for poor consumers.
Lower cereal prices can have substantial income effects for such
consumers, improving their ability to purchase non-staple foods that are
rich in bioavailable minerals and vitamins. Lower prices for non-staple
foods themselves, of course, also permit higher consumption of
micronutrient-dense foods. Consumer-preferred characteristics of food,
such as appearance, taste and color, can also be improved through
biotechnology, but such research probably benefits rich consumers more
than poor consumers in developing countries.

Ultimately, good nutrition depends on adequate intakes of a range of
nutrients and other compounds in combinations and levels that are not yet
completely understood. The best and final solution to malnutrition in
developing countries is to provide increased consumption of a range of
non-staple foods. By reducing the cost of producing food, biotechnology
will perhaps make its most important contribution to reducing
malnutrition. However, this will require several decades, informed
government policies and a relatively large investment in agricultural
research and other public and on-farm infrastructure to be realized.

In the medium run, a much smaller investment in breeding nutrient-dense
staple foods can make a major contribution to reducing deficiencies in
selected micronutrients. Because of the inherent compatibility of high
yields and trace mineral density, some successes in increasing the mineral
content of staples can be achieved in the short-run through conventional
breeding techniques. Plant breeding is a new strategy for improving
nutrition, and it is essential to make these early, nutritionally improved
varieties available to farmers for commercial production. Any resulting
improvements in micronutrient status must be measured to demonstrate the
feasibility and practicality of plant breeding for improving micronutrient
nutrition. Once feasibility and practicality are established for specific
crops and nutrients, the hope is that donor agencies will decide to accept
the relatively long lead times involved in plant breeding strategies and
that these agencies and agricultural research systems will adequately fund
the required research. The full potential of biotechnology can then be
applied to improving the nutritional content of food staples by (i)
perhaps increasing mineral levels even further than is possible with
conventional breeding techniques and (ii) pursuing complementary
strategies, such as adding beta-carotene and heat-stable phytase genes,
that are not possible using conventional breeding techniques.


REFERENCES
ACC/SCN (Administrative Committee on Coordination, Subcommittee on
Nutrition) and International Food Policy Research Institute (2000): Fourth
Report on the World Nutrition Situation. United Nations, Geneva.
Adrizal, P., E. Palo, and J.L. Sell (1996): Utilization of Defatted Rice
Bran by
Broiler Chickens. Poultry Science 75 (8), pp. 1012-1017.
Beard, J.L., J.W. Burton, and E.C. Theil (1996): Purified Ferritin and
Soybean Meal
Can Be Sources of Iron For Treating Iron Deficiency in Rats. Journal of
Nutrition 126, pp. 154-160.
Bouis, H.E. (1999): Economics of Enhanced Micronutrient Density in Food
Staples.
Field Crops Research 60, pp. 165-173.
Bouis, H.E., and L.J. Haddad (1990): Agricultural Commercialization,
Nutrition,
and the Rural Poor: A Study of Philippine Farm Households. Lynne Rienner
Publishers, Boulder.
Bouis, H.E., and M.J. Novenario-Reese (1997): The Determinants of Demand
for
Micronutrients: An Analysis of Rural Households in Bangladesh. FCND
Discussion Paper, International Food Policy Research Institute, Washington,
D.C.
Brown, P.H., Q. Zhang, and L. Ferguson (1994): Influence of Rootstock on
Nutrient
Acquisition by Pistachio. Journal of Plant Nutrition 17, pp. 1137-1148.
Cary, E.E., W.A. Norvell, D.L. Grunes, R.M. Welch, and W.S. Reid (1994):
Iron
and Manganese Accumulation by the brz Pea Mutant Grown in Soils. Agronomy
Journal 86, pp. 938-941.
Datta, S.K. (1999): The Genetic Engineering Approach to Development of
Nutritious Rice. Paper presented at the workshop “Improving Human Nutrition
Through Agriculture: The Role of International Agricultural Research”, 5-7
October, Los Baños, Philippines.
Falco, S.C., T. Guida, M. Locke, J. Mauvais, C. Sanders, R.T. Ward, and P.
Webber
(1995): Transgenic Canola and Soybean Seeds with Increased Lysine.
Biotechnology 13, pp. 577-582.
Farrell, D.J., and E.A. Martin (1998): Strategies to Improve the Nutritive
Value of
Rice Bran in Poultry Diets, III; The Addition of Inorganic Phosphorus and a
Phytase to Duck Diets. British Poultry Science 39 (5), pp. 601-611.
Foy, C.D. (1983): Plant Adaptation to Mineral Stress in Problem Soils.
Iowa State
Journal of Research 57, pp. 355-391.
Garcia-Casal, M.N., M. Layrisse, L. Solano, F. Arguello, D. Llovera, J.
Ramírez, I.
Leets, and E. Tropper (1998): Vitamin A and b-Carotene Can Improve Nonheme
Iron Absorption from Rice, Wheat and Corn by Humans. Journal of Nutrition
128, pp. 646-650.
Gibson, R.S. (1994): Zinc Nutrition in Developing Countries. Nutrition
Research
Reviews 7, pp. 151-173.
23
Goto, F., T. Yoshihara, N. Shigemoto, S. Toki, and F. Takaiwa (1999): Iron
Fortification of Rice Seed By the Soybean Ferritin Gene. Nature
Biotechnology
17, pp. 282-286.
Graham, R.D., and A.D. Rovira (1984): A Role for Manganese in the
Resistance of
What to Take-All. Plant Soil 78, pp. 441-444.
Graham, R.D. (1991): Breeding Wheats for Tolerance to Micronutrient
Deficient
Soil: Present Status and Priorities. In: D.A. Saunders (ed.). Wheat for the
Nontraditional Warm Areas. International Maize and Wheat Improvement
Center, Mexico City.
Graham, R.D., D. Senadhira, and I. Ortiz-Monasterio (1997): A Strategy for
Breeding Staple-Food Crops with High Micronutrient Density. Soil Science
Plant Nutrition 43, pp. 1153-1157.
Graham, R.D., D. Senadhira, S.E. Beebe, C. Iglesias, and I.
Ortiz-Monasterio
(1999): Breeding for Micronutrient Density in Edible Portions of Staple
Food
Crops: Conventional Approaches. Field Crop Research 60, pp. 57-80.
Graham R.D., and R.M. Welch (1996): Breeding for Staple Food Crops With
High
Micronutrient Density. Agricultural Strategies for Micronutrients, Working
Paper 3, International Food Policy Research Institute, Washington, D.C.
Gregorio, G. (1999): Research on Trace Minerals in Rice. Paper presented
at the
workshop “Improving Human Nutrition Through Agriculture: The Role of
International Agricultural Research,” 5-7 October, Los Baños, Philippines.
Grubb, P.J. (1994): Root Competition in Soils of Different Fertility: A
Paradox
Resolved? Phytocoenologogia 24, pp. 495-505.
Guerinot, M.L. (2000): The Green Revolution Strikes Gold. Science 287,
pp.241-
243.
Gura, T. (1999): New Genes Boost Rice Nutrients. Science 285, pp. 994-995.
Hallberg, L. (1981): Bioavailability of Dietary Iron in Man. Annual Review
of
Nutrition 1, pp. 123-127.
Han, Z.H., Q. Wang, and T. Shen (1994): Comparison of Some Physiological
and
Biochemical Characteristics Between Iron-Efficient and Iron-Inefficient
Species
in the Genus Malus. Journal of Plant Nutrition 17, pp. 1257-1264.
Hurrell, R.F. (1997): Bioavailability of Iron. European Journal of
Clinical Nutrition
51 (Supplement 1), pp. 4-8.
Kannenberg, L.W., and D.E. Falk (1995): Models for Activation of Plant
Genetic
Resources for Crop Breeding Programs. Canadian Journal of Plant Sciences
75,
pp. 45-53.
Levin, H., E. Pollitt, R. Galloway, and J. McGuire (1993): Micronutrient
Deficiency
Disorders. D. Jamison, W. Mosley, A. Measham, and J. Bobadila (eds.).
Disease
Control Priorities in Developing Countries. Oxford University Press, New
York.
Martin, E.A., J.V. Nolan, Z. Nitsan, and D.J. Farrell (1998): Strategies
to Improve
the Nutritive Value of Rice Bran in Poultry Diets, IV; Effects of Addition
of Fish
24 Howarth E. Bouis
Meal and a Microbial Phytase to Duckling Diets on Bird Performance and
Amino Acid Digestibility. British Poultry Science 39 (5), pp. 612-621.
Martinez-Torres, C., M. Renzi, and M. Layrisse (1976): Iron Absorption By
Humans from Hemosiderin and Ferritin, Further Studies. Journal of Nutrition
106, pp. 128-135.
McCay, B.T.S., D.M. Huber, R.D. Graham, J.D. Phillips, and K.E. Miskin
(1995):
Manganese Seed Content and Take-All of Cereals. Journal of Plant Nutrition
18,
pp. 1711-1721.
Misawa, N., S. Yamono, H. Linden, M.R. de Felipe, M. Lucas, H. Ikenga, and
G.
Sandmann (1993): Functional Expression of the Erwinia Uredovora Carotenoid
Biosynthesis Gene crtl in Transgenic Plants Showing an Increase of
b-Carotene
Biosynthesis Activity and Resistance to the Bleaching Herbicide
Norflurazon.
Plant Journal 4 (5), pp. 833-840.
Pasamontes, L., M. Haiker, M. Wyss, M. Tessier, A.P.G.M. van Loon (1997):
Gene
Cloning, Purification, and Characterization of a Heat-Stable Phytase from
the
Fungus Aspergillus Fumigatus. Applied Environmental Microbiology 63, pp.
1696-1700.
de Pee, S., C.E. West, D. Permaesih, S. Martuti, Muhilal, and J.G.
Hautvast (1998):
Orange Fruit Is More Effective Than Are Dark-Green, Leafy Vegetables in
Increasing Serum Concentrations of Retinol and b-Carotene in
Schoolchildren in
Indonesia. American Journal of Clinical Nutrition 68, pp. 1058-1067.
Pearson, J.N., and Z. Rengel (1995): Uptake and Distribution of Zn and Mn
in
Wheat Grown at Sufficient and Deficient Levels of Zn and Mn During Growth
Development. Journal of Experimental Biology 46, pp. 841-845.
Ponnamperuma, F.N. (1982): Genotypic Adaptability as a Substitute for
Amendments on Toxic and Nutrient-Deficient Soils. In: A. Seife (ed.). Plant
Nutrition 1982. CAB, Slough, UK, pp. 467-473.
Raboy, V. (1996): Cereal Low Phytic Mutants: A ‘Global’ Approach to
Improving
Mineral Nutritional Quality. Micronutrients and Agriculture, No. 2,
Federation
of American Scientists, Washington, D.C.
Rahman, S., G.F. Vance, and L.C. Munn (1993): Salinity Induced Effects on
the
Nutrient Status of Soil, Corn Leaves, and Kernels. Community in Soil
Science
and Plant Analysis 24, pp. 17-18.
Rengel, Z., and R.D. Graham (1995): Importance of Seed Zn Content for Wheat
Growth on Zn-Deficient Soil, I; Vegetative Growth. Plant and Soil 173, pp.
259-
266.
Rengel, Z., and R.D. Graham (1995): Importance of Seed Zn Content for Wheat
Growth on Zn-Deficient Soil, II; Grain Yield. Plant and Soil 173, pp.
267-274.
Schledz, M., S. Al-Babili, J. Lintig, H. Haubruck, S. Rabbani, H. Kleinig,
and P.
Beyer (1996): Phytoene Synthase from Narcissus Pseudonarcissus: Functional
Expression, Galactolipid Requirement, Topological Distribution in
Chromoplasts
and Induction During Flowering. Plant Journal 10 (5), pp. 781-792.
25
Senadhira, D., and R.D. Graham (1999): Genetic Variation in Iron and Zinc
Concentrations in Brown Rice. Micronutrients in Agriculture 3, pp. 10-12.
Sillanpaa, M. (1990): Micronutrient Assessment at the Country Level: An
International Study. FAO Soils Bulletin 48, Food and Agriculture
Organization
of the United States, Rome.
Skikne, B., D. Fonzo, S.R. Lynch, and J.D. Cook (1997): Bovine Ferritin
Bioavailability in Man. European Journal of Clinical Investigations 27,
pp. 228-
233.
Smith, J.C. (1996): The Vitamin A – Zinc Connection. Micronutrients and
Agriculture, No. 1, Federation of American Scientists, Washington, D.C.
Sparrow, D.H., and R.D. Graham (1988): Susceptibility of Zinc-Deficient
Wheat
Plants to Colonization by Fusarium Graminearum Schw. Group 1. Plant Soil
112, pp. 261-266.
Taylor, P.G., C. Martinez-Torres, E.L. Romano, and M. Layrisse (1986): The
Effect
of Cysteine-Containing Peptides Released During Meat Digestion on Iron
Absorption in Humans. American Journal of Clinical Nutrition 43, pp. 68-71.
Thongbai, P., R.J. Hannam, R.D. Graham, and M.J. Webb (1993): Zinc
Nutrition
and Rhizoctoria Root Rot of Cereals. Plant Soil 153, pp. 207-214.
Welch, R.M. (1986): Effects of Nutrient Deficiencies on Seed Production and
Quality. Advances in Plant Nutrition 2, pp. 205-247.
Welch, R.M. (1993): Zinc Concentrations and Forms in Plants for Humans and
Animals. In: A.D. Robson (ed.). Zinc in Soils and Plants. Kluwer Academic
Publishers, Boston, pp. 183-195.
Welch, R.M. (1996): The Optimal Breeding Strategy Is to Increase the
Density of
Promoter Compounds and Micronutrient Minerals in Seeds; Caution Should Be
Used in Reducing Anti-Nutrients in Staple Food Crops. Micronutrients and
Agriculture, No. 1, Federation of American Scientists, Washington, D.C.
Welch, R.M., W. House, S. Beebe, D. Senadhira, G. Gregorio, and Z. Cheng
(1999):
Testing Iron and Zinc Bioavailability in Genetically Enriched Bean
(Phaseolus
Vulgaris L.) And Rice (Oryza Sativa L.) Using a Rat Model. Paper presented
at
the workshop “Improving Human Nutrition Through Agriculture: The Role of
International Agricultural Research,” 5-7 October, Los Baños, Philippines.
Welch, R.M., M.E. Smith, D.R. van Campen, and S.C. Schaefer (1993):
Improving
the Mineral Reserves and Protein Quality of Maize Kernels Using Unique
Genes. Plant and Soil 171, pp. 155-156.
Wise A. (1995): Phytate and Zinc Bioavailability. International Journal of
Food
Science and Nutrition 46, pp. 53-63.
World Bank (1994): Enriching Lives: Overcoming Vitamin and Mineral
Malnutrition in Developing Countries. Development in Practice Series, World
Bank, Washington, D.C.
Ye, X., S. Al-Babili, A. Klöti, J. Zhang, P. Lucca, P. Beyer, I. Potrykus
(2000):
Engineering the Pro-Vitamin A (b-Carotene) Biosynthetic Pathway into
(Carotenoid-Free) Rice Endosperm. Science 287, pp. 303-305.