The Studay On Mechanism Of Pb Toxicity To Apple Stock M.hupehensis, M.micromalus And Comparison Of Their Tolerance

M. hupehensis and M. micromalus apple stock exposed to different concentrations of lead were used to study the effect of lead stress on Pb content in different organs, growth, photosynthesis and antioxidative enzymes such as SOD, CAT and POD. The main results were following:1. Lead was mainly accumulated in the roots of apple stock, and the content of lead in the leaves was the lowest. Under the lead stress of high concentration, the growth of apple stock was restrained significantly which was manifested as the decrease of biomass, root dry weight, shoot dry weight, raito of shoot/root and the content of water. The analysis of root dry weight, shoot dry weight, and the raito of shoot/root showed that the roots were the earliest organ affected by lead stress.2. Lead stress caused the appearance of brown spot in the leaves, accompanying green loss of the leaves. The content of chlorophyll a, chlorophyll b, the ratio of chlorophyll a to b and total chlorophyll content decreased with the increase of lead concentration, which led to the decrease of photosynthetic rate and growth rate finally.3. Lead stress led to the changes in antioxidant system of M. hupehensis and M. micromalus apple stock. The activities of SOD, CAT increased at the beginning of lead stress in all treatments, then the activities of them had a large drop with the increase of Pb concentration and the treatment time, which showed that there were activation effect at low lead concentrations and inhibition effect at high ones. However, the response of two cultivars to lead stress was not always the same in POD activity. POD activity of M. hupehensis increased continuously at any concentration and time, and the trend of POD activity of M. micromalus was similar to that of M. hupehensis, but the increase extent at low concentration was higher than that at high concentration. Meanwhile the content of ascorbic acid and carotenoid decreased significantly, which disturbed the balance of reactive-oxygen-species (ROS)system, causing the accumulation of ROS and MDA and the increase of membrane permeability. These results showed that lead stress caused oxidative stress of M. hupehensis and M. micromalus apple stock.4. The lead stress of high concentration decreased the activity of nitrate reductase and the content of soluble protein, which showed that the lead stress enhanced degradation and decreased synthesis of protein and plant growth was restrained.