| Drought stress can cause many adverse effects to the growth and development of plants, such as stomatal closure, leaf wilt, growth retardation, even plant death. Millet is one of China’s traditional food crops, with outstanding features of tolerance to drought and barrens. To explore the physiological changes of plant in the drought process, millet and Arabidopsis plants were used as materials, through field experiments and laboratory simulation drought stress, with the detection of osmotic adjustment contents, antioxidant enzyme activity and drought-related gene expression levels, and analyse the effect of SO2 on the physiology of drought, we achieved the following results:1. In order to obtain a better understanding of the drought tolerance of foxtail millet (Setaria italica L.) varieties, local variety named as "Jingu 20" was selected as the experimental material for field trials. Some biochemistry characteristics were assayed under both irrigation and drought stress conditions at the booting and filling stages. The results showed that the contents of proline and soluble sugar in foxtail millet flag leaves increased respectively 73.84% and 29.53% at the booting stage under drought stress, and while the activities of ascorbate peroxidase significantly increased 61.54%. Both hydrogen peroxide and malondialdehyde contents did not change much. However, at the filling stage, the contents of H2O2, MDA and Pro increased significantly as comparied with the non-drought plants, and also the enzymatic activities of APX, catalase and peroxidase increased markedly, but the content of soluble sugar decreased. These results indicated that foxtail millet variety Jingu 20 has strong resilience, self-regulation and adaptability to drought stress condition at booting stage. Conversely, foxtail millet plants are more sensitive to drought stress at filling stage. Pro and APX play important protective roles in foxtail millet plants in response to drought stress.2. SO2 is one of the most common atmosphere pollutants, a certain concentration of SO2 can induce oxidative stress response in plant, heighten the contents of reactive oxygen species, and activate cellular defense responses. Laboratory study found that a certain concentration of SO2 can reduce the physiological hazard of millet and Arabidopsis under drought stress.(1) Simulated drought group of 20% PEG-8000, the lengths of root and shoot in hydroponic millet were decreased 19.49% and 9.02%, with 0.4 mmol/L SO2 derivates pretreatment, the lengths of root and shoot were significantly increased 50.43% and 14.17%.(2) After drought stress 5 days, the contents of H2O2 and MDA in potted millet of 15 days were significantly increased 99.94% and 51.39%; after spraying 0.4 mmol/L SO2 derivates, the contents of H2O2 and MDA were significantly decreased 56.72% and 32.04%.(3) After drought stress 7 days, H2O2 and MDA contents in potted millet of 60 days were significantly increased 74.42% and 55%, soluble sugar and Pro contents increased by 41.99% and 2.03%, activity of superoxide dismutase was decreased 49.23%, POD activity was decreased significantly 21.22%; after spraying 0.7 mmol/L SO2 derivates, the contents of H2O2 and MDA in millet leaves were significantly decreased 37.39% and 33.74%, soluble sugar and Pro contents were significantly increased 120.85% and 98.59%, SOD and POD activities significantly increased by 411.49% and 62.37%.(4) After drought stress 5 days, the contents of H2O2 and MDA in Arabidopsis of 4 weeks were significantly increased 61.49% and 77.48%, Pro content was significantly increased 133.12%, activity of SOD was increased 23.33%, POD activity significantly decreased by 41.08%; after spraying 0.4 mmol/L SO2 derivates, levels of H2O2 and MDA were significantly reduced 37.06% and 42.06%, Pro content was significantly increased 84.02%, activities of SOD and POD significantly increased by 38.44% and 210.75%.(5) After drought stress 5 days, expression of DREB2A, DREB2B and RD29A in the ground tissue of Arabidopsis were upregulated, expression of MIR398a and MIR398c were downregulated, expression of CSD2 was upregulated; after spraying 0.4 mmol/L SO2 derivates, expression quantity of DREB2A, DREB2B and RD29A were greater than the drought stress group, declines of MIR398a and MIR398c were higher than the drought stress group, increases of CSD2 was higher than the drought stress group.The result of these researches shows that drought stress can increase the contents of reactive oxygen species in millet and Arabidopsis, bring about oxidative damage; however, a certain concentration of SO2 derivates pretreatment can promote the growth of plant seedlings under drought stress, lighten the degree of withering plant leaves, enhance the antioxidant enzyme activities of plant, make expression of the drought-related genes upregulate and transcriptional levels of miR398 downregulate, improve the abilities of plant to adapt to adversity, and reduce the oxidative damage caused by drought stress on plant, enhance the plant tolerance to drought stress; in other words, pretreatment of SO2 derivates can relieve oxidative damage caused by drought stress with a certain extent, and then provide the basis for application in the process of SO2 in plant drought resistance. |
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