Agriculture Reference
In-Depth Information
ability to reduce arsenate to arsenite by same enzyme; this reaction is similar to
yeast in terms of arsenate reduction, substrate specificity and sensitivity towards
inhibitors.
In the resistance mechanism of arsenic the level of phytochelatins is increased
because arsenite binds with phytochelatins. Phytochelatins are heavy metal bind-
ing peptides derived from glutathione (GSH) with the general structure (γ-glu-
cys)nGly. The biosynthesis of phytochelatins involves the transpeptidation of
γ-glutamyl-cysteinyl dipeptides from GSH by the action of constitutively expressed
phytochelatins synthetase (Grill et al.
1987
). Recent studies have confirmed that
As(III) is complexed with phytochelatins in a range of terrestrial plant species, sug-
gesting that phytochelatins play an important role in decreasing the toxicity of ar-
senic in crops (Hartley-Whitaker et al.
2001
; Zhang et al.
2012
). Recently, Duana
et al. (
2011
) has suggest that PC complexation of arsenite in rice leaves reduces As
translocation from leaves to grains, and implicate that manipulation of PC synthesis
might mitigate As accumulation in rice grain. Similarly induced levels of PCs were
also observed in
O. sativa
(Tripathi et al.
2012
a) under As stress.
MolecularChangesinPlantsExposedtoArsenic
There are several molecular responses by plants towards exposure to arsenic, due
to both arsenic toxicity and also due to arsenic tolerance. Arsenic affects the ex-
pression of many genes that are involved in various essential cellular processes
in plants. A number of genes involved in cell growth, cellular morphogenesis and
cell cycle are down regulated on exposure to arsenic. From the study of the rice
genome, two expansion genes (OsOlg14660 and Os04g46650), two tubulin genes
(Os03g45920 and Os03g56810), an actin gene (OsOlg64630) and two microtubule
genes (Os03g13460 and Os09g27700) which are involved in cell cycle and cell
growth are less expressed when exposed to arsenic at low concentration for long
term exposure (Norton et al.
2008
). In As(V)-treated rice seedling, a triose-phos-
phate/Pi translocator gene was transcriptionally up-regulated (Chakrabarty et al.
2009
). This protein would be expected to transport Pi and As(V) across the plastid
inner membrane in exchange for triose-phosphate. The effect of As exposure on
genome-wide expression was also examined in rice (Yu et al.
2012
). An As tolerance
gene has been identified and mapped to chromosome 6 in rice (Tripathi et al.
2012
a).
A signaling molecule Nitric oxide, was also found to be induced during As(V) stress
condition in
A. thaliana
(Leterrier et al.
2012
).
The genes responsible for the expression of nutrient uptake transporters are re-
sponding differentially in arsenic toxicity. Norton et al. (
2008
) has also revealed that
genes for transporters of various nutrients differentially expressed in rice genome.
For phosphate, chloride, ammonium and nitrate transporters are down regulated
which possibly cause nutrient deficiency in plants while sulphate transporters are
up regulated, this is may be due to increased uptake of sulphur for the synthesis of
Search WWH ::
Custom Search