Physiological Responses Of Rye Seedlings To Freeze–thaw With Different Minimum Temperature And Chloride Deicing Agent Stress And Subsequent Recovery

Freeze–thaw?FT?and deicing agent are common stresses to the plants in urban areas of middle and high latitudes.The early spring temperature fluctuations usually lead to the variation of the freeze–thaw intensity in northeastern China.Therefore,the physiological changes of different FT intensities?i.e.-3?FT:10,5,0,-3,0,5,10?;-5?FT:10,5,0,-5,0,5,10?;-7?FT:10,5,0,-7,0,5,10??and sodium chloride?NaCl?and subsequent recovery on rye?Secale cerale L.Dongmu–70?were studied in this paper.What's more,the physiological responses of Dongmu–70 rye seedlings under different FT intensities and NaCl stress were compared to provide theoretical basis for Dongmu–70 ryes overwintering in Northeast China under different FT intensities.The physiological indicators determined in this study were:superoxide dismutase?SOD?,soluble protein,malondialdehyde?MDA?,relative water content?RWC?,chlorophyll?Chl?,net photosynthetic rate?A?,transpiration rate?E?,intercellular CO₂ concentration?Ci?,stomatal conductance?gs?and water use efficiency?WUE?.The results showed that:Compared to control,seedlings exhibited an increase in the SOD activity,the content of protein and MDA under NaCl stress.This was accompanied by a decrease in the RWC,Chl content,A,E,Ci,gs and WUE.At T4?-3,-5,or-7??,compared to the control?CK?,seedlings exhibited an increase in SOD activity in all treatments.This was accompanied by a decrease in RWC.Protein content increased in combined stress of-5?FT and NaCl group?NFT-5?.In contrast,it decreased in combined stress of-3 and-7?FT and NaCl groups?NFT-3 and NFT-7?,while the change of MDA content was just the opposite.At T4 and the recovery period,the changes of SOD activity,protein content and RWC in combined stress groups showed a similar pattern as-5?>-3?>-7?.Furthermore,after FT cycles and 7 days recovery,the Chl content,A,E,Ci and gs in all treatments were lower than those in the control,and the WUE values in all treatments decreased except those in NFT-5.After seven days recovery,Chl content,A,E,Ci and gs values recovered more in NFT-5 than those in NFT-3 and NFT-7,and WUE in NFT-5 decreased less than those in NFT-3 and NFT-7.The results of Pearson correlation analysis exhibited that MDA content was positively correlated with SOD activity under single FT stress,protein content was positively correlated with SOD activity under FT stress and combined stress of-3 and-5?,and there wae a significant negative correlation between protein content and RWC under FT-5 and NFT-5?P?0.05?.Our results and corresponding discussion highlight the importance of considering proper FT intensity?i.e.-5??to the cold resistance of rye seedlings under NaCl stress.