Biology Reference
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variability for kernel micronutrients (like Fe and
Zn) in maize germplasm and breeding for kernel
Fe- and/or Zn-enriched elite maize germplasm
assume considerable significance.
Studies undertaken by CIMMYT and IITA
in collaboration with national partners have led
to identification of some elite maize lines with
high levels of kernel Fe and Zn in both normal
maize (e.g., Banziger and Long 2000; Menkir
2008; Prasanna et al. 2011; Chakraborti et al.
2011a) as well as QPM genetic backgrounds
(Chakraborti et al. 2011b). A study undertaken
in India (Chakraborti et al. 2011b) demonstrated
that despite dilution effect, QPM genotypes have
considerable potential, particularly in Zn bio-
fortification programs, as compared to the non-
QPM. The apparent homeostasis for kernel Zn
concentration of the QPM inbreds and hybrids
may be possibly attributed to the pleiotropic
effect of
opaque-2
allele or its close linkage with
genes responsible for accumulation of higher Zn
(Arnold et al. 1977; Gupta et al. 1980). Cur-
rently, the CIMMYT-Harvest Plus-maize pro-
gram is pursuing a large-scale GWAS (genome-
wide association study) for identifying genomic
regions influencing kernel Zn and Fe in the trop-
ical germplasm background.
phenomenon can contribute to human mineral
deficiency, particularly with respect to iron and
zinc. It has been demonstrated that substantial
reductions in feed phytic acid result in improve-
ments in calcium and zinc utilization. Efforts to
increase Fe and its bioavailability in maize ker-
nels have been limited due to the low Fe genetic
diversity found in maize. Bioavailabity screening
was also researched as an option for developing
biofortified Fe maize, but the screening proce-
dures and low diversity are not highly encourag-
ing (Pixley et al. 2011). Bioavailable Fe has been
achieved through transgenic approaches reduc-
ing phytate (Drakakai et al. 2001).
The first use of normal-phytate and low-
phytate isolines in a human nutrition study eval-
uated fractional absorption of iron from tortillas
(Raboy 2002), demonstrating an improvement of
49% for low phytate over normal lines. A simi-
lar study found that fractional absorption of zinc
from an
lpa1
-
1
maize food was 30%, whereas
it was 17% from normal maize (Adams et al.
2000). Dietary phytic acid may also have benefi-
cial health roles, for example as an antioxidant or
anticancer agent. The relative merits or demer-
its of dietary phytic acid, therefore, depends on
the characteristics of the target populations. For
example, children and pregnant woman in devel-
oping countries who are at the greatest risk for
mineral deficiencies and dependent on cereals
and legumes as staple foods may benefit from
a diet that is significantly reduced in phytic
acid content. On the other hand, a subpopulation
that might benefit from dietary phytic acid may
be aging adults in the developed world (Raboy
2002), where the anti-cancer/anti-oxidant effect
of phytic acid is notable.
In the context of poultry and swine produc-
tion, feeds are based largely on cereal grains and
oilseed meals. Approximately two-thirds of the P
in cereal grains and oilseed meals is present in the
form of P bound to phytic acid (phytate P), which
is not digested by poultry and largely excreted
in the manure, which contributes to water pol-
lution. Phytic acid-derived P in animal waste
can contribute to environmental pollution, a
Low Phytate Maize
The nutritional quality of cereals and legumes
depends on the major seed phosphorus stor-
age compound, phytic acid (
myo
-inositol-
hexa
kis
phosphate). Phytic acid forms one to sev-
eral percent of seed dry weight and typically is
deposited in seeds as mixed phytate or phytin
salts of potassium and magnesium. Phytic acid P
represents from 65 to 85% of seed total P. Phytic
acid is an effective chelator of positively charged
cations. When consumed in feeds and foods,
phytic acid will bind to nutritionally important
mineral cations in the intestinal tract, such as
calcium, iron, and zinc, and to proteins as well,
making them unavailable biologically. Humans
and non-ruminants, such as poultry, swine, and
fish, excrete a large fraction of these salts. This
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