Agriculture Reference
In-Depth Information
dry weight of
Zea mays
cultivars. Ghnaya et al. (
2005
) reported that Cd severely in-
hibited
Mesembryanthemum crystallinum
growth even at low concentration. Wahid
et al. (
2007
) observed increased shoot Cd accumulation and leaf chlorosis with a
concomitant reduction in shoot dry weight, leaf area, relative growth rate, net as-
similation rate and relative leaf expansion rate in
Vigna radiata
seedlings under Cd
stress. Kachout et al. (
2009
) showed that exposure of plants to different levels of
metal (Cu, Ni, Pb, Zn) reduced the DM production and height of shoots in
Atriplex
hortensis
and
A. rosea
. The decrease in root growth caused by toxicity of metals was
more severe than the decrease in shoot growth. Atriplex plants exhibited gradual de-
cline in height when exposed to following metal (a 4-week exposure of
A. hortensis
to 25, 50, 75, and 100 % contaminated soil). Kuriakose and Prasad (
2008
) reported
that at concentrations above 3.0 mM Cd, seed germination of
Sorghum bicolor
was
adversely affected with a complete cessation of seedling growth. Skorzynska-Polit
and Baszynski (
1997
) reported that Cd-induced necrosis of leaf tissues might be
the reason of Cd mobilization and its transport to plant parts above the ground.
Cadmium has been shown to affect the photosynthetic functions through interacting
with photosynthetic apparatus at various levels of organization and architecture,
viz., accumulation of metal in leaf (main photosynthetic organ), partitioning in leaf
tissues like stomata, mesophyll and bundle sheath cells, interaction with cytosolic
enzymes and alteration of the functions of chloroplast membranes. Anjum et al.
(
2011
) reported that mung been (
Vigna radiata
) seedlings treated with Cd (25, 50,
and 100 mg CdCl
2
kg
−1
soil) caused significant decrease in the dry weight and leaf
area, photosynthetic parameters (net photosynthetic rate and chlorophyll content).
The increasing level of Cd in soil resulted in a gradual decrease in plant dry weight,
leaf area, photosynthesis, and chlorophyll content in both
V. radiata
genotypes. At
100 mg Cd kg
−1
soil, the plant dry weight, leaf area, photosynthesis and chlorophyll
content were reduced by 59.8, 39.8, 30.8, and 40.0 %, respectively in Cd-suscepti-
ble cv. PS 16 as compared to the control, but in Cd-tolerant cv. Pusa 9531, decreases
in these parameters were 26.2, 23.0, 27.5, and 36.3 %, respectively. Farouk et al.
(
2011
) observed that Cd at 100 and 150 mg kg
−1
soil decreased the length, fresh
and dry weights of shoot and root systems as well as leaf number per plant, signifi-
cantly. Chlorophyll, total sugars, nitrogen, phosphorus, potassium, relative water
content, water deficit percentage and soluble proteins as well as total amino acid
contents were also decreased. John et al. reported that
Brassica juncea
plant exhib-
ited a decline in growth, chlorophyll content and carotenoids with Cd and Pb but
Cd was found to be more detrimental than Pb treatment in it. The protein content at
the flowering stage decreased by 95 % due to Cd (900 μM) and by 44 % due to b
(1500 μM). Cd has been shown to be the most effective inhibitor of photosynthetic
activity (Bazzaz et al.
1974
; Huang et al.
1974
), particularly the oxygen-evolving
reactions of photosystem II (Bazzaz and Govindjee
1974
; Baszynski et al.
1980
;
Atal et al.
1991
). With only a small amount of Cd in chloroplasts, many direct and
indirect effects are observed, resulting in strong inhibition of photosynthesis. Most
researchers connect the reduction of chlorophyll (Chl) in Cd-treated plants with
inhibition of its biosynthesis. Stobart et al. (
1985
) established that Cd inhibited
chlorophyll biosynthesis at two levels —in the synthesis of 5-aminolaevulinic acid
