Environmental Engineering Reference
In-Depth Information
Fig. 4.2  Relationship between dry (DM) and fresh mass (FM) (%) after 10 days growth of S. alba
L. in the presence of tested metals; mean of three determinations, standard deviation 6 % or less
(  R —root; S —shoot; Con. —control)
our results, Burd et al. ( 1998 ) and Chatterjee and Chaterjee ( 2000 ) also reported that
root growth was as a more sensitive indicator of metal toxicity than shoot growth.
Here-in, this was significantly confirmed mainly for chromium. The general re-
sponse of decreased root growth due to Cr and other metal toxicity may be evoked
by the inhibition of root cell division/root elongation or by the extension of the cell
cycle in the roots. Under high concentrations of Cr, Ni and many other heavy met-
als, the reduction of root growth may be due to the direct contact of seedling roots
with a metal present in the medium, causing collapse, and subsequently inability of
roots to absorb water from the medium (Barcelo et al. 1986 ). Adverse effects of Cr,
Ni and other metals on plant height and shoot growth were reported by Rout et al.
( 2000 ) and Barton et al. ( 2000 ). The significant reduction in plant height of S. alba
observed in this present study was also reported for this plant by Hanus and Tomas
( 1993 ) in soil with Cr concentrations of 200 or 400 mg/kg. The reduction in plant
height may be due mainly to the reduced root growth and consequent lesser nutri-
ent and water transport to the shoots. Additionally, Cr and Ni transport to the aerial
parts of the plant can have a direct impact on the cellular metabolism of shoots, thus
contributing to the reduction in plant height (Shanker et al. 2005 ).
The overall adverse effects of Cr and Ni on growth and development of plants
may be a serious impairment of mineral nutrients and water uptake, which leads to
deficiency in the shoots. Wilting of various crops and plant species due to Cr toxic-
ity has been reported (Turner and Rust 1971 ), but little information is available on
the exact effects of Cr and Ni on water relations in higher plants. When the relation-
ship between dry (DM) and fresh mass (FM) was determined herein (Fig. 4.2 ), the
DM fraction was increased parallel to increased Cr and Ni concentrations, while for
FM fraction the growth trend was opposite. The effect of tested metals was stronger
on FM than on DM production, and root FM was reduced more strongly than that
Search WWH ::




Custom Search