Studies On Screening Of Rice(Oryza Sativa L.)Germplasm Tolerant To Cd Stress And Its Characteristics Of Physio-biochemistry

72 rice cultivars with different Cd tolerance were screened by adding Cd in the hydroponic culture nutrition. The results indicated a significant genotypic variation of Cd tolerance in the tested 72 cultivars. The cluster analysis of tolerance indices, including shoot height and its dry weight, root length and its weight of rice plants exposed to 0.2mg/L Cd level , showed that 72 rice genotypes may be grouped into four clusters, i.e. Cd sensitive genotype, relatively sensitive genotype, tolerant genotype and relatively tolerant genotype. Of 72 rice cultivars, Lemont, 1R98-22, Lanbeili, F6-143-1, Dular, Yumijing5, R669. and so on, were the most tolerant, F6-138-1 was the most sensitive.The Cd contents of various plant parts at different Cd levels and different time and the physio-biochemical characteristics of functional leaves were studied in two rice cultivars(F₆-138-1 and Lemont) with different Cd-tolerance according to the previous screening experiment. The results were summarized as follows:It was showed that Cadmium accumulation in root and shoot of two rice cultivars increased with increasing external Cd levels and the time of Cd exposure. The pattern of Cd accumulation and partitioning is: root?straw>sheath>leave>kernel. The higher Cd concentration in kernel of F₆-138-1 compared to Lemont could be believed that it was more sensitive to Cd ToxicityThe genotypic differences in the effect of Cd on the content of chlorophyll was studied. It was show that 0.8mg/L Cd stress caused a sharp decline in chlorophyll content.and chlorophyll a showed more sensitive to Cd toxicity than chlorophyll b.There was a highly significant difference in the reduction of chlorophyll content in 2 rice concerned.A hydroponic experiment was carried out to study genotypic difference in effect of three Cd levels on activities of antioxidant enzymes in functional leaves of rice seedlings. A highly significant increase in MDA content, and a stimulation of SOD, POD and CAT activities were recorded in the plants subjected to 0.8mg/L Cd, and the effect increased with both Cd concentration and the time of exposure.during 7¹4d. Although the activity of SOD reduced significant at 21d, but that of POD increased. There was the significant genotypic difference in activities of antioxidant enzymes.The genotypic difference in potential antioxidant capacity between...