Effect Of Copper On Rice Germination And Growth And Accumulation Of Copper In Brown Rice In Different Rice Cultivars

A pot experiment with 38 commonly cultured rice cultivars showed that the effect of Cu (100 mg kg^-1) on rice growth, grain yield and accumulation of Cu in brown rice varied greatly with different cultivars. Although the average Cu concentration in brown rice of the 38 cultivars was significantly increased (P< 0.01) compared with the control, in none of the cultivars did Cu concentration in brown rice exceed the maximum permissible limit of 10 mg Cu kg^-1. This suggests that rice grown in Cu-contaminated paddy soil (100 mg Cu kg^-1) will not adversely affect human health through the food chain. Because of the significant negative correlation between grain weight and Cu concentration in brown rice with the soil Cu treatment, screening for cultivars with low Cu accumulation in brown rice and high grain yield for Cu-contaminated areas is feasible. The present research led to the recommendation of three such cultivars: Jiahua, Zhenxian 866, Zhe 733. The average grain yield under Cu treatment (100 mg Cu kg^-1 soil) was significantly (P<0.01) reduced compared with the control. The decreases or increases of grain yields mainly resulted from the combined effects of the panicles per pot, spikelets per panicle and filled spikelets per panicle under the soil Cu treatment. Furthermore, there were significant (r = 0.869, P<0.01) positive correlations between the RC (relative changes) of spikelets per panicle and filled spikelets per panicle under the soil Cu treatment.Furthermore , this study also conducted to investigate the effect of copper on the seed germination of different rice cultivars. The results showed that the root elongation was more easily inhibited than coleoptile by copper stress (0.1 mM and 0.2 mM), and the effect of copper on root elongation differed markedly between cultivars. We also investigated the cell mitosis and Ca²⁺ localization in cells of rice root tips under copper treatment (25, 50, 75, 100 μM), and the results showed that both the mitotic index and the relative mitotic index decreased with the increase of copper concentration. Moreover, the mitotic index and the relative mitotic indexshowed increases under a certain copper concentration, as time prolonged. The changes of Ca2+ localization in cells of rice root tips under copper stress (50 /*M) were investigated with calcium antimoniteprecipitate-electronmicroscopic-cytochemical methods. When rice seedlings grew under the normal condition, it was shown that the deposits of calcium antimonite, being indicator for Ca2+ localization, mainly concentrated within the vacuoles and intercellular spaces, and the free Ca2+ in cytoplasm and nucleus is very low under the normal condition. When the seedling were grown under the 50 juM CUSO4 for 12 h, the level of Ca2+ in cytoplasm and nucleus increased, while the level in vacuole and intercellular spaces decreased. Based on the above observations, the author proposed that the changes of Ca2+ localization in the cells of rice root tips could disturb cellular metabolism by disrupting Ca2+ homeostasis and affect the growth of roots.