Physiological And Biochemical Response Mechanism Of Osmanthus Fragrans ’Tian Xiang TaiGe’ To Drought And Heat Stress

To clarity the physiological and biochemical response of Osmanthus fragrans ‘Tian Xiang TaiGe’ to drought and heat stress,this study treated O.fragrans ‘Tian Xiang TaiGe’ seedlings under artificial simulated drought and heat stress environment(control,light,moderate and heavy)and analyzed the change of light response curve,chlorophyll fluorescence intensity,reactive oxygen species content,antioxidant activity and antioxidant content.The main conclusions were as follows:(1)Pmax and AQY decreased gradually with the increase of drought stress.Under combined drought and heat stress,Pmax and AQY decreased significantly compared to the drought stress.LCP increased significantly after drought and heat stress,but there was no significant change in LSP.LCP and LSP was futher improved under combined drought and heat stress compared to single stress.(2)The determination results of fluorescence parameters such as φP0,φE0 and φD0 sh0 wed that the quantum yield decreased after single drought and heat stress;Parameters like ABS/CS0,TR0/CS0,ET0/CS0 and DI0/CS0 indicated that the unit excitation light reactive state area was reduced significantly under single drought and heat stress,photosynthetic efficiency decreased much after combined drought and heat stress.With the enhanced of drought stress intensity,DI0/RC and RC/CS0 improved significantly,which were increased 416.1%(P < 0.05)and 123.4%(P < 0.05)relatively after heavy stress compared to the control;PIABS was significantly decreased 84.6%(P < 0.05)compared to the control.(3)The content of ROS and MDA enhanced significantly after single drought and heat stress,and had the trend of first increased and then decreased under the combined stress.The activity of SOD,CAT and POD increased significantly after single stress,and the change trend was increase at first and then decreased after the combined stress.The AsA content and its reducing power(AsA/DHA)decreased with the increasing of stress degree when the GSH content and its reducing power(GSH/GSSG)increased first and then decreased.The activity of APX,DHAR,MDHAR and GR increased significantly after drought,heat and combined stress,which improved 42.0%(P <0.05),41.7%,75.7% and 39.2% relatively after light combined stress compared to light drought stress.In conclusion,after drought and heat stress,the photosynthetic efficiency decreased when ROS was accumulationed,membrane lipid peroxidation was increased.O.fragrans ‘Tian Xiang TaiGe’ could quickly start the antioxidant defense system to improve the non-enzymatic antioxidant content and antioxidant activity,which can maintain the balance of ROS,improved the body reducing capacity and showed a strong tolerance to drought and heat stress.This ability was more obvious in single stress and weakened significantly after light and moderate combined stress,the physiological function was disordered and could not be defended against combined heavy stress.