Agriculture Reference
In-Depth Information
chromium-stressed plants could have been due to the inhibition of the activity of
the plasma membrane H
+
-ATPase. The decrease in ATPase activity causes a de-
crease in proton extrusion. This in turn causes a decrease in the transport activities
of the root plasma membranes and reduces the uptake of some nutrient elements.
Moreover, chromium interfered with the mechanism controlling intracellular pH.
This hypothesis was supported by the fact that chromium could be reduced in the
cells thereby utilizing the protons (Zaccheo et al.
1982
). For the chromium action
in the translocation of mineral nutrients, it is known that Phosphorous and chro-
mium are competitive for surface root sites and iron is also known to be in competi-
tion with chromium for transport binding, inducing iron deficiency (Chatterjee and
Chatterjee
2000
). Chromium causes severe decrease in calcium concentration in the
leaves even though calcium is necessary for the development of the cell wall and
the maintenance of membrane structure (Marschner
1999
) of the leaves. Chatterjee
and Chatterjee (
2000
) and Sinha et al. (
2006
) have reported that
Brassica oleracea
and
Vigna radiata
plants stressed with chromium presented manganese (Mn) defi-
ciencies. However, other studies showed that Cr(VI) supply increased manganese
content in
Citrullus vulgaris
(Dube et al.
2003
). Chromium by inducing competitive
phenomena in root assimilation and translocation in plants with other mineral ele-
ments, may therefore indirectly affect water status and plant growth.
Chromium interacts with Nitrogen (N), phosphorous, potassium (K), aluminum,
chloride (Cl) and zinc (Zn), thereby influencing the plant metabolism. It simulta-
neously affects the content of many minerals, thereby leading to severe mineral
imbalance in the plant. Inhibition in the uptake of potassium was observed owing
to plant treatment with Cr(VI), which was dependent on both the incubation pe-
riod and the concentration of chromium applied (Zaccheo et al.
1982
). Similarly,
chromium-induced reductions in the Nitrogen, Magnesium, phosphorous and potas-
sium contents and increases in the aluminum, iron and zinc contents are on record
(Gardea-Torresday et al.
2005
; Davies et al.
2001
; Vernay et al.
2007
). Calcium
uptake can be restricted by chromium treatment (Gardea-Torresday et al.
2005
).
Since phosphorus and chromium are competitive inhibitors, they share an antago-
nistic relationship with each other, resulting in a lower phosphorus level, the effect
being more prominent in leaves and roots in comparison to stem. Chromium also
enjoys structural similarity with other essential elements like iron and sulphur, thus
interfering with the uptake of these elements. The reductions in the nutrient contents
like Nitrogen, phosphorous and potassium, could be due to the reduced root growth
and impaired absorption of these minerals.
4.4 Chromium Toxicity to Carbon Assimilation of Plants
Carbon assimilation of plant is impaired by chromium toxicity in terms of CO
2
fix-
ation, electron transport, photophosphorylation and enzyme activities (Vernay et al.
2007
). In presence of higher chromium concentrations,
L. perenne
plants present a
decrease of calcium content in leaves of about 13-fold compared to control plants.
