Effects Of Cadmium And Lead On The Grain Yield And Quality Of Rice And Their Distributions In The Plants

Cadmium (Cd) and lead (Pb) are important contaminants in agricultural soil and threatening agriculture and human health. In this study, three high-yielding rice cultivars currently used in the local production, Yangdao 6 (indica), Wuyunjing 7 and Yangjing 9538 (japonica), were pot-grown, and different treatments of Cd and Pb concentrations, various soil moistures and nitrogen (N) levels were conducted to clarify the effects of Cd and Pb on the grain yield and quality of rice and their uptakes and distributions in the plants. The main results are as follows:1. The grain yeild of Yangdao 6 was increased at a low concentration of Cd, whereas it was reduced at a high concentration, when compared with that at the control (without Cd). The grain yields of Wuyunjing 7 and Yangjing 9538 were reduced with the increase in Cd concentrations. The yield of Yangdao 6 was reduced by 2.65% at the low concentration of Pb, and reduced by 3.92% at the high concentration. Pb treatments, either at a low or a high concentration, reduced the grain yields of Wuyunjing 7 and Yangjing 9538. Both Cd and Pb treatments reduced the breakdown value and increased the setback value in the starch-profile, suggesting that Cd and Pb make the poorer in the eating and tasting quality of rice. Cd and Pb were not distributed uniformly in each part of rice plants. The accumulation of Cd or Pb in plants was higher at high concentrations than at low concentrations, and that in roots>stems>leaves>panicles. Cd at a high concentration significantly increased Cd accumulation in each part of a grain. Pb at a high concentration significantly increased Pb concentration in grains and accumulation in husks of Yangdao 6, whereas it had no significant effect on those of Yangjing 9538.2. The grain yield was high under moderate dry-wet alternate irrigation (MD) than that under well watered (WW) or under severe dry-wet alternate irrigation (SD) when Cd or Pb was not added into the soil. The grain yield was significantly reduced under MD and SD when Cd or Pb was treated. Under both MD and SD, the Cd treatment increased the breakdown value and reduced the setback significantly. Pb treatment significantly increased the breakdown value of Yangjing 9538, but little affected the setback value, suggesting that both Cd and Pb improve the eating and tasting quality when dry-wet alternate irrigation was imposed. The concentration and accumulation of Cd and Pb in the plants were increased with the decrease of soil moisture, indicating that low soil moisture could enhance the uptake of Cd and Pb in plants. The dry-wet alternate irrigation reduced the accumulation of Cd in the husk and chaff, whereas increased Cd in the polished rice, indicating that low soil moisture enhances the translocation of Cd to kernels.3. Under the same heavy metal treatment, the grain yield was increased with the increase in N levels. Cd or Pb treatment reduced the yield when N level was the same. Under the Cd treatment, the breakdown value was reduced and the setback value was increased with the increase in N levels. Under the Pb treatment, the breakdown value was increased while the setback value eas reduced when MN was applied, and the result was reversed when HN was applied. The accumulations of Cd and Pb in plants were increased with the increase in N levels.4. Cd at a high concentration and Pb at both low and high concentrations induced the expression of catalase (CAT) isozymes in rice leaves. Under different treatments of soil moisture and N levels, Cd or Pb inhibited the expression of some isozymes, meanwhile enhanced the expression of some new isozymes, of superoxide dismutase (SOD), or peroxidase (POD) or CAT. The types and degrees of the isozymes inhibited or enhanced varied with the concentrations of Cd or Pb, soil moistures and N levels.