Rice Genomics and Genetics 2015, Vol.6, No.9, 1-9
3
Liang et al. (2007) has been investigated the
variation of phytic acid (PA), iron (Fe) and zinc (Zn)
levels in 56 varieties of Chinese rice. Fe levels
showed the biggest variation (9~45 mg/kg) and were
not related with PA content or grain shape. Zn
showed a moderate variability (13~39 mg/kg),
which was narrower than for Fe, while broader than
for PA (7.2~11.9 g/kg).
Banerjee et al. (2010) analyzed variability in grain
protein and Fe/Zn levels in 46 rice lines including
indica
and
japonica
rice cultivars, germplasm
assesions, advanced breeding lines and wild rice
genotypes and reported large variation for grain
protein and micronutrient levels among the tested
rice genotypes, which ranged from 6.19 to 10.75%
for grain protein content, 4.82 to 22.69 mg/kg (µg/g)
for grain Fe and 13.95 to 41.73 mg/kg (µg/g) for
grain Zn content. Ezeonu et al. (2002) analyzed Fe
and Zn concentrations in water, soil and staple food
samples including rice. Zinc and iron concentration
in rice varied from 3.5.0~15.0 mg/kg (ppm/l) and
20.0~75.0 mg/kg (ppm/l) respectively.
The molecular understanding of metal homeostasis
in plants in general and rice in particular, with the
knowledge of the physiology of metal uptake,
translocation and movement across the cell membranes
will provide a basis to design strategies for
development of micronutrient rich staple foods
(Chandel et al., 2010). This can be achieved by
identification and critical functional characterization
of genes involved in metal uptake and transport in
rice. Several molecular players have been identified
with speculated functions in transporting minerals
into the plants such as those belonging to
ZIP
,
NRAMP
and
YSL
family of transporters (Maser et al.,
2001, Gross et al., 2003, Kobayashi et al., 2005).
Rice genes orthologous to
NAS
and
NAAT
genes of
barley (
Hordeum vulgare
L)
viz OsNAS1
,
OsNAS2
and
OsNAS3
have also been isolated (Tomako et al.,
2007) and characterized for functions in metal
uptake and translocation. These genes, which are
related to the phytosiderophore biosynthetic pathway,
have been shown to be involved in iron acquisition
during germination (Koike et al.,
2004). Mineral-rich
and mineral-poor rice genotypes identified in this
study could be an ideal material for such molecular
and physiological analyses.
2 Micronutrient malnutrition the hidden-
hunger
Micronutrient malnutrition is the condition that
develops when the body does not get the optimum
amount of the vitamins, minerals and other
micronutrients which are essential to maintain
metabolic regulation and organ function. Among the
major nutritional problems common in developing
countries are: micronutrient (iron, zinc, vitamin A)
and protein-energy malnutrition (Zimmermann and
Hurrell, 2002; Bouis et al.
,
2003; Welch and
Graham, 2004). It is estimated that over 800 million
people go to bed hungry every day and approximately
3 billion people are suffering from micronutrient
deficiency (Evans 1998). More than half of the
world’s population, especially women and children
in the developing countries, suffer from micronutrient
malnutrition or ‘hidden hunger’ resulting from the
consumption of meager bioavailable vitamins and
minerals containing diets (UN SCN, 2004).
Plant biologists can provide a crucial input in this
fight to reduce micronutrient malnutrition by
producing staple foods whose edible portions are
denser in bioavailable minerals (such as iron, zinc)
and vitamins. “Biofortification” refers to the
development of micronutrient-dense staple crops
using the best traditional breeding practices and
modern biotechnology (Gregorio, 2002; Pfeiffer and
McClafferty, 2007; White and Broadley, 2005). This
approach has multiple advantages. First, it capitalizes
on regular daily intake of a consistent and large
amount of staple food by all family members,
because staple foods are predominantly consumed
by the poor people. Second, after the one-time
investment to develop seeds that fortify themselves,
recurrent costs are low, and germplasm can be
shared internationally. Third, biofortification provides
a feasible mean of reaching undernourished
populations in relatively remote rural areas,
delivering naturally fortified foods to people with
limited access to commercially marketed fortified
foods that are more readily available in urban
areas/developed nations (Nestel et al., 2006).
Iron deficiency is the most common micronutrient
deficiency in the world Globally, anemia affects
more than 1.6 billion people, or approximately 25%
of the population. In developing countries,
