Agriculture Reference
In-Depth Information
Fig. 14.2
Transportation index of field-grown Indian mustard as influenced by duration and doses
of chromium exposure. T0, T1, T2, T3, T4 and T5 are the treatments with 0, 100, 200, 300, 400 and
800 mg Cr kg
−1
soil, respectively.
DAS
days after sowing. Results are presented as means ± stan-
dard error (n = 3). Values followed by same letters are not significantly different at p < 0.05
3 Translocation of Chromium in Plants
Once chromium is absorbed by roots from nutrient solution, it is poorly translocated
elsewhere and largely retained in the roots itself (Zayed et al.
1998
). The transporta-
tion index is used to work out the ability of plants to translocate heavy metal from
the root to the aerial harvestable plant parts. It varied with duration and doses of
chromium exposure (Fig.
14.2
). Transportation index of Indian mustard has been
worked out at various levels of chromium application. Shoot concentrations of chro-
mium barely exceeded one-hundredth of those in roots, regardless of the chromium
species supplied (Parr and Taylor
1980
). The restriction in the translocation of both
chromium forms in plants to the same degree, despite the differential accumulation
in roots and shoots, suggests that conversion of Cr(VI) to Cr(III) is almost certain to
occur in roots. Since the predominant species of chromium in roots is Cr(III), very
little translocation of chromium to the shoot is expected to occur when plants are
supplied with either forms of chromium. Supporting evidence for this hypothesis
comes from chromium uptake studies when chromium was supplied in chelated
forms. A marked enhancement in the translocation of chromium to plant tops was
observed when chromium-EDTA, which is not retained by ion exchange, was sup-
plied as compared to the ionic forms of chromium (Athalye et al.
1995
). In addition,
Skeffington et al. (
1976
) illustrated that Cr(III) and Cr(VI) enter the vascular tissue
with difficulty; however, once in the xylem, chromium moves more readily. Even
