Variable tolerance of two genotypes of rice to excess copper

To assess comparative copper tolerance and its inhibitory effect on metabolism of rice (Oryza sativa L.) two genotypes viz. Pusa Basmati and Pusa Sharbati were grown in refined sand in complete nutrient solution for 36 days after sowing. On 37^th day plants were divided into 3 lots. One lot was allowed to grow with complete nutrient solution to serve as control (0.001 mM Cu) while the other two lots were supplied with excess copper (as copper sulphate) at 0.1 and 0.2 mM, respectively. After 9 days of metal supply (d 46), at 0.2 mM Cu, growth of rice was depressed and young leaves developed marginal interveinal chlorosis. Later the effects intensified and irregular brown necrotic spots developed on the affected leaves. With increase in age the affected leaves were completely bleached, The symptoms were delayed by seven days in plants at 0.1 mM Cu. Excess copper reduced the biomass, concentration of chlorophylls a, b, total and active iron and activities of catalase, acid phosphatase and polyphenol oxidase and increased the activity of peroxidase in leaves. In both the genotypes, the accumulation of Cu was higher in roots, than leaves, more so in Pusa Sharbati than Pusa Basmati. Rice genotype Pusa Sharbati appears to be more sensitive to Cu toxicity.