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0 5 10 15 Ni (ppm) in irrigation water

April

Ni (ppm) in irrigation water

Ni (ppm) in irrigation water

Fig. 16.2 Net photosynthetic rate (|rmol/m2/s), transpiration rate (E), conductance (C), and internal relative humidity (RH in) in the LTM leaves of sugarcane irrigated with 0, 5, 10, and 15 ppm Ni (bars represent ± SEM). From Rai et al. (2006)

hexavalent chromium were investigated in sugarcane variety CoSe 92423. The inhibition of shoot and root growth due to chromium was concentration dependent. Maximum germination was obtained at 30 ppm of chromium. This was due to an increase in antioxidative enzyme activity and the operation of the glutathione-ascorbate cycle to scavenge toxic levels of H2O2. Despite a reduction in growth, dry matter production increased substantially as the chromium concentration was increased. Significant increases in lipid peroxidation and tissue concentrations of H2O2 were observed in plants exposed to 30, 60 and 90 ppm Cr. Chromium affected the glutathione reductase and ascorbate peroxidase activities in roots and leaves differently. Glutamyl cysteine synthetase activity increased for Cr levels of up to 60 ppm, but it decreased slightly at 90 ppm, although even at this level it still remained higher than that of the control. The chromium-induced suppression of sugarcane plant growth was considered to be a function of the increased cellular accumulation of chromium despite increases in the activities of antioxidative enzymes. Cr supplied through irrigation water containing 15 ppm of the metal decreased photosynthesis by 50% 30 days after treatment (DAT) during March. The Cr treated plants recorded an overall decrease in photosynthetic rate with increasing Cr concentration (Fig. 16.3). Cr treatment increased the transpiration rate at 30

Cr in irrigation water (ppm)

April

Cr in irrigation water (ppm)

April

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