Effects Of Drought Stress On Physiological And Biochemical Response And Expansin Expression Profiles In Foxtail Millet (Setaria Italica) Seedlings

Drought stress is one of the most important factors that affect the yield of foxtail millet in agricultural production.To research on the adaptive mechanism and investigate the physiological responses and biochemistry pathways in Setaria italica under drought stress,three varieties with different drought tolerance of foxtail millet were selected.We measured series of physiological and biochemical parameters of foxtail millet leaves during seedling stage under drought stress,such as activities of antioxidant enzyme,malondialdehyde(MDA)content and proline(osmotic adjustment substances)content.The dynamic changes of net photosynthetic rate(Pn),stomatal conductance(Cond),intercellular CO2 concentration(Ci),transpiration rate(Tr),and water use efficiency(WUE)were also measured.In addition,we analyzed the relationship between expansin gene family and drought stress in foxtail millet.The main results of these experiments were as follows:1.Under drought stress,the activities of SOD,POD and CAT in three varieties of foxtail millet leaves were increased in different degrees,influenced by light and darkness.The SOD activity of DTI and DT2 were significantly increased,more than DT3 under both light and dark conditions.For DT2,the POD and SOD activities were increased under both light and dark conditions,and the scale of the increase was higher under light condition.The correlation analysis showed that,in DTI and DT2,SOD had significant correlation with both POD and CAT;there was also significant correlation between POD and CAT.In DT3,there was no significant correlation among the three physiological and biochemical parameters.The MDA content was all increased;In addition,in DTI and DT3,the rate of increase under light condition is higher than in the dark;the content of proline in leaves was also increased during the seedling stage,and sharply increased under the light condition,which was much higher than in the dark.2.Pn,Cond,Ci,Tr and WUE were decreased gradually with the aggravation of drought stress in all three varieties of foxtail millet;The Ci of DTI and DT3 was decreased gradually,whereas it was increased firstly and then decreased in DT2.The Pn of three varieties of foxtail millet showed a trend of increasing and then decreasing during the drought process.After re-watering,the Pn,Cond,Ci,Tr,and WUE were increased in all materials,the photosynthetic ability was recovered,which were lower than the control group but there was no significant difference between the control group and the drought experiment group.3.In foxtail millet,the number of introns among expansin gene family members(EXPA,EXPB,EXPLA and EXPLB)was conserved.Through the analysis of their promoters,we found a number of responsive elements related to drought stress.The expression level of SiEXP15 gene was probably related to drought tolerance.