Responses Of Brassica Species To Arsenic Stress And Their Mechanisms

Arsenic is a highly toxic and carcinogenic microelement widely existed in nature. After consuming plants with certain accumulation of arsenic, the health of the animals and human being will be at stake, which could be of hidden threat to food safety and living conditions. Rape, a kind of field crop widely planted in southern China, has been affected by arsenic pollution in different degrees. Based on the reviews of arsenic bioavailability to plants, solution culture and soil culture experiments were conducted to investigate the different physiological responses and mechanisms between different rapes which are planted in arsenic polluted soil. The main results were as follows:1. Some rape varieties tolerant to arsenic were selected via hydroponic culture added with arsenic. The results indicated that there were 16 varieties selected as As tolerant, namely J176, J296, J286, J110, J085, J245, J148, J200, J062, J039, J045, J208, J059,071,041,097, featuring as higher aerial and underground biomass ratio, smaller root cap, and larger amount accumulation of As in root system; sensitive varieties were J008, J010, J069, J022, J214, J282,001,025, with the characterization of lower biomass and higher accumulation of As in underground part; seven low-absorption varieties were J179, J135, J098, J237,007,075,091, with higher biomass than control but lower As accumulation. For further As pot experiment, six typical As tolerant- and sensitive-varieties were selected from these 31 varieties, which were J200, J062,071,041, J022,025.2. The effects on growth and yields of different rape cultivars were investigated under arsenic stress. The results indicated that the biomass, yield and fruitage of J200, J062,071,041 were higher than that of the control and J022 and 025 were not. Fruitage of J062 increased by 47.2% and thousand grain weight of J200 increased by 30.6% compared with the controls. The results concluded that As tolerant rapes were better choices to plant when arsenic concentration in the soil is up to 100 mg/kg.3. The effects on kinetics of As uptake and root exudates of rapes under arsenic stress were analyzed. The results indicated that, for As3+, sensitive rapes had higher Imax, lower Cmin and Km and tolerant ones showed the opposite trend. The main organic acids exuded from different rapes were oxalic acid and malic acid. Compared with the control, oxalic acid and malic acid exuded from J062 decreased by 44.5% and 30.5% respectively,45.0% and 15.5% as for 071.4. Concentration and form of arsenic in rape tissues were investigated. The results indicated that most arsenic was accumulated in rape roots but difficult to transfer upward. Arsenic in roots and shoots of rapes exsited as As3+ and As5+, but As3+ was the main species, its content in leaves and roots were more than 70% and 80%. The content of As5+ of J022,025 is higher than the others.5. The responses of enzymatic antioxidant, non-enzymatic antioxidant and photosynthesis systems of rape tissues were investigated. The results indicated that the activities of enzymatic antioxidants (superoxide dismatase-SOD, and catalase-CAT) and the contents of non-enzymatic antioxidants (glutathione-GSH, ascorbic acid-AsA, and malondialdehyde-MDA) in tolerant rapes increased and sensitive rapes did not. They played an important role in decreasing arsenic toxicity.Chlorophyll content in the six selected varieties was elevated in the pot experiment, but chlorophyll a/b ratio was increased in tolerant varieties and decreased in sensitive ones at bolting stage. As stress improved the photosynthetic rate in tolerant varieties, but reverse phenomenon was observed in the sensitive ones.