Effects of drought and salinity combined stress on activities of physiological characteristics in Avena nuda seedling leaves

The pot culture experiment was conducted to study the response to drought and salinity combined stress of reactive oxygen species(ROS),including O2-· and H2O2,as well as malondialdehyde(MDA)content and antioxidative system in leaves of naked oat(Avena nuda L.‘Dingyou No'6)seedlings.The results showed that the cell membrane was seriously damaged due to the disturbed ROS metabolism,activities of cell antioxidant enzymes and antioxidant content.Catalase(CAT)activity and glutathione(GSH)content increased,ascorbic acid(AsA)content decreased.Superoxide dismutase(SOD),peroxidase(POD),and ascorbate peroxidase(APX)increased to the peak and then decreased.Furthermore,O2-· generation rate and contents of H2O2 and MDA significantly increased in leaves of naked oat seedlings.Compared with the control soil,salinity of 0.3% significantly enhanced the activities of SOD,POD and APX in leaves under the conditions of low drought stress(65% soil field capacity)and medium stress(50% soil field capacity).In addition,soil salinity at 0.6% showed no significant influence on ROS and MDA under mild drought stress.But it significantly increased O2-· generation rate and contents of H2O2 and MDA under moderate drought stress.Under severe drought stress(35% soil field capacity),activities of SOD,CAT,POD and APX,and contents of AsA and GSH in naked oat leaves significantly decreased,while O2-· generation rate and contents of H2O2 and MDA increased with degree of salinity stress.These findings suggest that low stress of salinity(0.3%)could partially repair the oxidative damages induced by slight or medium drought stress.