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The phytotoxicity due to nickel (Ni) and its accumulation in castor (Ricinus communis L.) plant of Euphorbiaceae family resulting from its addition from low to very high levels to a swell-shrink clayey soil (Haplustert) was studied in a pot culture experiment. Nine levels of Ni (0, 10, 40, 80, 120, 160, 180, 200, 250 mg Ni kg−1 soil) were applied. Crop was harvested at 45 days after sowing. At the higher Ni levels, beyond 200 mg Ni kg−1 soil, reduced growth symptom was recorded. The concentration of Ni in plant parts increased with increasing dose of applied Ni. Nickel concentration in castor root ranged from traces (control) to 455 mg kg−1 and was directly related to soil Ni concentration. At 200 mg Ni kg−1 soil, dry matter yield of castor reduced to 10% of control plant. Significant changes were observed in the roots of castor treated with higher levels of Ni against control. The roots treated with Ni showed a decrease in number of cells in the cortex region. It also appeared that the cortex region consisted of elongated parenchymatous cells instead of the normal parenchymatous tissue as in the control plant. Regarding Ni accumulation capacity, castor plant was recorded as an accumulator (α = 0.11 and β = 1.10). A laboratory study was also conducted in the experimental soil to know the different operationally defined fractions of Ni, which control the availability of Ni to castor. Different fractions of Ni present in this soil followed this order: Residual > Fe-Mn oxides > carbonate > organic > exchangeable > water soluble Overall results depict that castor is a promising species which can be used as a potential plant for phytoremediation of contaminated soils and to improve soil quality and provide economical benefits. [ABSTRACT FROM PUBLISHER]

To better understand the mechanisms responsible for differences in uptake and distribution of cadmium (Cd), nutrient-solution experiments were conducted with different varieties of rice ( Oryza sativa ), ‘Khitish’ and ‘CNRH3’. The plants were grown in a complete nutrient solution with different levels of pCd (-log free Cd +2 activity) and pFe [-log free iron (Fe +2 ) activity]. The required concentrations of chelating agent and metals were determined using a computerized chemical equilibrium model such as Geochem-PC. Experimental treatments included a combination of four pCd activity levels (0, 7.9, 8.2, and 8.5) applied as Cd (NO 3 ) 2 4H 2 O, and two pFe activity levels (17.0 and 17.8) applied as FeCl 3 . The application of both Cd and Fe in solution culture significantly affected plant growth, yield, and Cd accumulation in plant tissue. In general, yield of rice was decreased by an increase in amount of solution Cd; however, yield response varied among the cultivars. At the 7.9 pCd level, yields of rice cultivars ‘Khitish’ and ‘CNRH3’ were reduced to 69% and 65%, respectively, compared with control plants. Root Cd concentrations ranged from 2.6 mg kg -1 (control plants) to 505.7 mg kg -1 and were directly related to solution Cd concentrations. In rice plants, Cd toxicity symptoms resembled Fe chlorosis. Differential tolerance of varieties to phytotoxicity was not readily visible, but a significant interaction of substrate Cd and variety was obtained from dry-matter yields. Significant interactions indicated that response of tissue Cd concentration, plant Cd uptake, and translocation of Cd to the aerial parts were dependent on variety as well as substrate Cd. Uptake of Cd by roots was significantly higher than by shoots. Higher Cd uptake by rice plants decreased the uptake of other beneficial metals. The effect of Cd and Fe on the rate of phytometallophore release was also studied in the nutrient solution. Among the rice genotypes, ‘Khitish’ was the most sensitive to Cd toxicity. In both genotypes, with the onset of visual Cd-toxicity symptoms, the release of phytometallophore (PM) was enhanced. Among the rice varieties, ‘Khitish’ had the highest rate of PM release. Treatments with the metal ions studied produced a decrease in chlorophyll and enzyme activity. A decrease in concentrations of chlorophyll pigments in the third leaf was observed due to the highest activity level of Cd (pCd 7.9). Activities of enzymes such as peroxidase (POD) and superoxide dismutase (SOD) are altered by toxic amounts of Cd. Changes in enzyme activities occurred at the lowest activity of Cd (pCd 8.5) in solution. Peroxidase activity increased in the third leaf. Results showed that in contrast with growth parameters, the measurements of enzyme activities may be included as early biomarkers in a plant bioassay to assess the phytotoxicity of Cd-contaminated solution on rice plants. Evidence that Cd uptake and translocation are genetically controlled warrants the selection of varieties that assimilate the least Cd and that translocate the least metal to the plant part to be used for human and animal consumption. [ABSTRACT FROM AUTHOR]

The phytotoxicity due to cadmium (Cd) and its likely contamination of the food chain—resulting from its addition from low to very high levels to a swell-shrink clayey soil (Haplustert) in spinach ( Spinacia oleracea L.)—was studied in a pot culture experiment. Twelve levels of Cd (0, 2, 4, 8, 10, 20, 40, 60, 80, 120, 160, 200 mg kg -1 soil) were applied singly and in combination with two doses (0 and 2.5 cm) of spent wash. Above 80 mg Cd kg -1 soil, there was very slow growth of spinach after germination. Spinach crop suffering from severe Cd toxicity had small roots and narrow yellowish leaves, covered in small necrotic spots. Higher levels of Cd inhibited the growth and biomass of the crop. However, application of spent wash alleviated the toxic effect of Cd to some extent. The concentration of Cd in plant parts increased when Cd was applied singly but decreased considerably when used in combination with spent wash. Cd concentration in spinach root ranged from traces (control) to 120 mg kg -1 dry matter and was directly related to soil Cd concentration. At 40 mg kg -1 soil, yield of spinach was reduced to 38% of control plants. A laboratory study was also conducted in the soils collected from treated pots after harvest in order to know the different operationally defined fractions of Cd that control the availability of Cd to spinach and that were correlated with dry-matter yield of spinach crop. [ABSTRACT FROM AUTHOR]