Agriculture Reference
In-Depth Information
and (c) increased uptake of Cr(VI) leading to increased chromium levels in leaves,
which in turn results in oxidative stress and chlorosis of leaves (i.e., leaf-induced
iron deficiency).
4.2 Chromium Toxicity to Growth and Development of Plants
Growth of root and shoot has been traditionally considered as a valuable trait for
scoring heavy metal tolerance in plants. For instance, this trait is widely used to
select plant varieties for tolerance to aluminum, a metal that strongly limits agri-
cultural production in acidic soils. Root growth arrest caused by chromium can be
considered as a toxicity symptom (Diwan et al.
2010a
). Roots serve as an interface
between the soil and plants. Being in direct contact with heavy metals (HM), roots
play a dominant role in preventing plants from adverse HM effects. Chromium in
the soil affects root growth adversely, depending on its concentration and the plant
species. Root growth was completely inhibited in
Vigna radiata
and
V
.
sinensis
with
chromium treatments ranging from 40 to 160 ppm (Jamal et al.
2006
). In
Salvia,
root growth inhibition was evident at 10 mg L
−1
; not only the main root elongation
but the lateral root development was also affected. Speciation of chromium also
has a bearing on root growth (Corradi et al.
1993
). Reductions in root growth in
Vigna radiata
cv CO4, as determined by dry weight of roots, were more pronounced
with Cr(VI) than with Cr(III) (Shanker et al.
2004
). The inhibitory effect of chro-
mium in roots could be due to the accumulation of high chromium concentrations
in roots, and non-existence of any defined translocation mechanism for chromium
thereby enhancing its sequestration in the tissue and thus inhibiting the root devel-
opment. The other reasons for reduced root growth may include inhibition of cell
division, root elongation or cell cycle extension in the roots. The direct contact of
roots with metals results in a collapse of roots and their inability to absorb water
from the media (Barcelo et al.
1986
; Sanita di toppi et al.
2002
). Chromium af-
fects shoot development adversely by inhibiting growth of stem axis. Reduced plant
height was reported in pea, tomato, cauliflower, maize and green gram plants under
chromium stress (Hunter and Vergnano
1953
; Shanker et al.
2004
). Application of
Cr(III) (20 mg L
−1
) was inhibitive for
Salsola kali
but ineffective for
Oryza sativa
(Mishra et al.
1997
). The reduction observed in shoot length and biomass accumu-
lation could be due to impaired root growth leading to lesser uptake of essential
nutrients and water and the consequent impact on the cellular metabolism of shoot.
4.3 Chromium Toxicity to Mineral Nutrition of Plants
Chromium, due to its structural similarities with some essential elements, can
affect mineral nutrition of plants in a complex way. Fernandes et al. (
2002
) and
Moreira et al. (
2005
) have reported that the decrease uptake of these elements in
