Physiological Characteristics Of Rye Seedlings Under Freezing-thawing And Alkaline Salt Stress

There is a large area of saline-alkali land in Northeast China,and the composition is priority to alkaline salt.At the same time,it is also a zone where freezing-thawing phenomenon occurs frequently.Freezing-thawing and saline-alkali stress can cause changes in the physiological and ecological characteristics of plants.In this study,rye（Secale cerale.L cv.WinterGrazer-70）used the as experimental material,the changes of non photosynthetic physiology（osmotic adjustment substances,cell membrane lipid peroxidation and antioxidant enzyme activities）in rye seedlings under alkaline salt stress and freezing-thawing injury,and the changes of photosynthetic characteristics in rye seedlings during freezing-thawing recovery was investigated,so as to understand the adaptive characteristics in the rye seedlings and it also provide a theoretical basis for the cultivation of the rye in Northeast China.Some indicators were measured in this study:relative water content（RWC）,soluble protein,proline,malondialdehyde（MDA）,hydrogen peroxide（H₂O₂）,ascorbate peroxidase（APX）,catalase（CAT）,Superoxide dismutase（SOD）,peroxidase（POD）,net photosynthetic rate（A）,transpiration rate（E）,cell gap（Ci）,stomatal conductance（gs）and water use efficiency（WUE）.The results were as following:The results on the changes of non-photosynthetic physiological responses of the rye seedlings showed that RWC decreased under alkaline salt stress,MDA and H₂O₂content and APX,SOD,CAT and POD activity increased in leaves of the rye seedlings.At the freezing stage,RWC decreased at-5℃,the content of MDA and proline and the activity of APX,SOD and POD of rye seedlings increased in freezing-thawing group and compound stress group,and reached the maximum value at-5℃.The H₂O₂ content and CAT activity in the compound stress group reached the maximum at 0℃which showed that the damage is larger at 0°C and-5°C in rye,at the same time,the cells were frozen and dehydrated which showed that the plants were severely damaged.At the thawing stage,RWC showed the tendency of firstly increased then decreased,and the content of proline,MDA and the activity of SOD decreased with the increase of temperature in leaves of the rye in freezing-thawing group and compound stress,while the content of H₂O₂ and APX decreased at 0℃（T5）,there was no significant change in the subsequent thawing process.The content of proline,MDA and H₂O₂ and the activity of APX,SOD and POD in the leaves of the rye seedlings were almost the same as tendency of the compound stress group>freezing-thawing group>alkaline salt group>control group except 10℃（T1 and T7）,and under the compound stress,the seedlings harmed most seriously.During freezing-thawing recovery period,RWC and the content of soluble protein decreased in leaves of rye seedlings were treated with single freezing-thawing and compound stress.The content of MDA and proline and the activity of APX,CAT,SOD,POD was still higher than the control,indicating that the freezing-thawing injury to seedlings 6 days after recovery was still exist,but it was alleviated.Pearson correlation analysis showed that either freezing-thawing or compound stress,CAT in the rye seedling leaves were the main antioxidants to eliminate H₂O₂.The results on photosynthetic physiological characteristics of rye seedlings showed that the value of A,E,WUE,and gs were decreased and the Ci was increased during freezing-thawing recovery period after alkaline salt,freezing-thawing and compound stress.It was shown that the photosynthetic structure in rye seedlings was damaged caused by stress above caused a decrease in photosynthetic rate.The correlation analysis showed that there was a significant correlation between A and E after single freezing-thawing treatment（P<0.05）,and there were a significant correlation between gs and A,E after compound stress treatment（P<0.05）.On the 6th day after recovery,the value of A were almost the same as tendency of the compound stress group<freezing-thawing group<alkaline salt group<control group.