Physiological Responses Of Antioxidant Enzyme System To Alkali-saline Mixed Stress In The Seedlings Of Kochia Sieversiana

One of ecological crises people were facing was land salt-alkalinization. Salinationand alkalization usually occurred at the same time in some inland salt-alkalinized areas,because of the complex components of salts in them. Consequently, there were two kindsof stress viz. saline stress and alkaline stress in salt-alkalinized soil for plants. So theresearches in physiological responses of plants to salt-alkaline mixed stress not only werethe complement to plant stress physiology but also provided the foundation forecological improvement of salt-alkaline land.Kochia sieversiana (Pall.) C. A. Mey. was a native alkali resistant halophyte, andwas used as the material of experiment. Twenty five kinds of natural salt-alkalineecological conditions with different salinity and alkalinity (the range of total saltconcentration 100-500mmol/L, pH 7.14-10.51) were simulated by mixing NaCl, Na2SO4,NaHCO3 and Na2CO3 in various proportions. Seedlings of K.sieversiana were treatedunder these salt-alkaline conditions. Several strain indices such as superoxide dismutase(SOD) activity, catalase (CAT) activity, peroxidase (POD) activity, reactive oxygenspecies (ROS) content, and protein content were determined to analyze the responsespeciality of antioxidant enzyme system to salt-alkaline mixed stress in K.sieversiana.The results showed that K.sieversiana could grow under high salt-alkalineconditions even when the salinity reached 500mmol and pH10.51. It was proved thatK.sieversiana was a halophyte species with great tolerance to salinity and alkalinity. Theresponse value of five strain indices of K.sieversiana seedlings closely correlated notonly with salinity but also with the alkalinity (pH) of the treatment solution. Theactivities of three antioxidant enzymes in K.sieversiana seedlings showed regularlychanges with increasing saline stress. The activity of SOD increased firstly and thendecreased with increasing salinity while the activities of POD and CAT (excepted theactivity of CAT in 500mmol was slightly decreased) were increased with increasedsalinity. The effects of alkaline stress on antioxidant enzymes in K.sieversiana seedlingswere different with saline stress, and showed that the activity of SOD decreased withincreasing alkalinity and the activities of POD and CAT were increased with increasedalkalinity (only the activity of CAT in 500mmol was decreased). The contents of proteinand reactive oxygen species in K.sieversiana seedlings increased with increased salinity.Under alkaline stress, the contents of protein decreased with increased alkalinity whereasthe contents of reactive oxygen species increased with increased alkalinity. The results ofvariance analysis and correlation analysis showed that the effects of salinity andalkalinity on these strain indices were all reached significant level (P<0.001). Forantioxidant enzymes, the effects of salinity were more significant than of alkalinity,whereas for the contents of protein and reactive oxygen species the effects of alkalinitywere more significant than salinity. The results of this experiment validated theviewpoint that salt stress and alkaline stress were two kinds of different stresses, andshowed there were correlations as well as differences between them. The changing ofactivities of antioxidant enzymes activities in K.sieversiana seedlings had importantfunction for K.sieversiana to adapt to the environment of salt-alkaline mixed stress.