Intraspecific Differences Of Rice (Oryza Sativa L.) Cultivars In Cd Tolerance

As a result of industrial activities, fertilization and waste disposal, pollution of heavy metals in agricultural soils has becoming increasingly serious throughout the world. In China large areas of contaminated land can not afford to be abandoned from agricultural practice because of the demand for food. To minimize the influx of pollutants to human food chain through agricultural products, we conceptualized the cultivars whose edible parts accumulate certain pollutant at low enough level for safe consumption while grown in contaminated soil as'pollution-safe cultivar'(PSC). We validate the existence of Cd-PSC and feasibility of the PSC concept using pot experiments by growing 43 cultivars of rice (Oyza sativa L.). And the nutritional quality of grain and the existing forms of Cd in grain were analyzed. Main results are summarized as follows:1. Repeated pot experiments were conducted to study the genotypic difference in Cd uptake and accumulation in 43 rice cultivars (including 20 normal and 23 hybrid cultivars) under a high (75.69 mg kg-1) and a low level (1.75 mg kg-1) of Cd exposure. The results showed that under the two Cd exposure levels and in all the tested tissues, Cd concentrations varied significantly among the 43 tested cultivars. Under the low level of Cd exposure,30 out of the 43 tested cultivars were found to be Cd-PSCs. This suggests that the Cd accumulation in grain is genotype-dependent and the selection of PSCs at certain level of soil contamination is feasible. No Cd-PSC was found under the high level of Cd exposure, which suggests that the selection of PSC is contingent on soil contamination level. There was no significant difference of grain and straw yield between rice plants grown under the low and the high level of soil Cd exposure, so the fitness of the plants does not provide any warning about the toxicity of the grains. It is, therefore, important and practical to screen the PSCs and establish PSC breeding to effectively and efficiently reduce the risk of human exposed to soil pollutants via crop consumptions.2. Crude protein and amylose content in grains were analyzed. Under slight and heavy Cd stress, protein content in grain varied from 5.88% to 8.45% and from 5.58% to 7.39%, respectively. The range of drop for all cultivars was 1%-23%. Amylose content in grain considerably decreased under heavy Cd stress, and the average decreased from 18.79% to 16.29%. There was no significantly correlation between protein content and Cd content, and the same with amylose and Cd content.distribution and chemical forms of Cd in grain were studied through solvent extraction. Although the extraction ration of Cd was different among several rice cultivars, the sequence was same as FEDTA,FNAC1,FHAC,FNaOH>FW>FE.The average ration of 0.1 M EDTA extractable-Cd in Cd-PSCs grain was considerably lower than that in non-Cd-PSCs, probably because that the ability of binding Cd in non-Cd-PSCs grain is stronger than that Cd-PSCs.2.5%NaCl and 0.2%NaOH extractable-Cd in Cd-PSCs grain was higher than that in non-Cd-PSCs, which indicates that the ration of Cd bounded to protein in Cd-PSCs grain is more than the latter. According to the different solubility of the seed protein in various solvents, albumin, prolamin, globulin and glutelin were differentiated. The analysis showed that the concentration of binding Cd in globulin and glutelin was the higher, and the prolamin was the least.5% NaCl extractable-Cd in Cd-PSCs grain was more than that in non-Cd-PSCs, which was basically same with the former results.