Effect Of Lanthanum(Ⅲ) On Reactive Oxygen Metabolism Of Soybean Seedlings Under Supplemental UV-B Irradiation

UV-B radiation has given rise to numerous disadvantageous influences on crops'morphological structure, growth and development, physiology and biochemistry and so on. Rare earth of appropriate dosage could enhance crops'metabolism and relieve injury to them caused by such adverse stresses as acid rain, ozone, heavy metal, pesticide pollution. Therefor, soybean seedlings (Glycine max.) of"Kennong 18", which are sensitive to UV-B radiation, were utilized as our experimental objects. Effect of lanthanum(Ⅲ) on reactive oxygen metabolism of soybean seedlings under elevated ultraviolet-B radiation (UV-B: 280~330nm) at 15μW·cm-2 and 45μW·cm-2 levels respectively was studied through hydroponics in laboratory. The aim was to provide macroscopically physiological and ecological references for elaborating the mechanism of RE inducing plants'resistance to UV-B radiation at the molecular level, to widen the applied fields of RE technology, to offer another new ecological defense strategy for preventing crops from UV-B radiation, and to enrich the theory of ultraviolet-B radiation ecology. The major experiment results are shown as follows:(1)Firstly, effect of La(Ⅲ) on antioxidative indices of soybean seedlings was studied. Our results show that LaCl3 solution with the dose of 10, 20, 30, 40 and 50 mg·L-1 could increase activities of catalase(CAT) and peroxidase(POD) of soybean seedlings, decrease plasmolemma permeability and malonadialdehyde(MDA) content, improve antioxidative metabolism and promote growth and development of soybean seedlings. Our study only reflected the stimulative action of Hormesis effect. The optimal effect of LaCl3 solution with the dosage of 10, 20, 30, 40 and 50 mg·L-1 on antioxidative metabolism of soybean seedlings emerged on the third day. The optimal spraying dosage of LaCl3 solution for soybean seedlings was 20mg·L-1 and its promoting influence on reactive oxygen metabolism of soybean seedlings could at least maintain thirteen days.(2)Secondly, effect of La(Ⅲ) on membrane lipid fatty acids of soybean seedlings under UV-B radiation was analyzed. Our results indicate that although the components of soybean seedlings'membrane lipid fatty acids of all treatments were the same as those of CK, the proportion of membrane lipid fatty acids changed. The percentage of linolenic(18:3) decreased while that of palmitic(16:0) and stearic(18:0) increased when soybean seedlings were stressed by UV-B radiation. Therefor, index of unsaturated fatty acids (IUFA) decreased, which coincided with the dosage-dependent rule. With the add of La(Ⅲ), reactive oxygen metabolism of soybean seedlings was improved, the decline tendency of unsaturated fatty acids was slowed down and the rise trend of saturated fatty acids was controlled. Consequently, membrane lipid peroxidation was abated, IUFA increased and the preferable alleviative effect was obtained. The mitigatory effect of La(Ⅲ) on low UV-B radiation was better than that on high one. Associated with plasmolemma permeability, MDA concentration, the accumulation amount of H2O2 and water-holding capacity of soybean seedlings, one reason why UV-B radiation led to damage to...