Protective Mechanism Of Exogenous Spermidine On Salinity Stressed Chrysanthemum Seedlings

Chrysanthemum(Chrysanthemum morifolium)is one of chinese traditional famous flowers and world's four major cut flowers.Chrysanthemum usually applied as potted plants,cut flowers and garden flowers,it has important ornamental value and economic value,but sensitive to salt stress,so it is urgent to improve the salt tolerance of chrysanthemum.In this study,we take the chrysanthemum cultivars 'Qx096'(salt sensitive)and 'Qx097'(salt tolerant)as experimental materials,the endogenous polyamine content of the 2 chrysanthemum varieties exposed to salinity stress were determined,and Spd was selected for exogenous addition;Then studied the effect of 0.5 mM,1.0 mM,1.5 mM,2.0 mM exogenous Spd on chrysanthemum growth,photosynthetic gas parameters,Na+ and K+content,soluble protein and proline(Pro)content,antioxidant enzyme activity and MDA content.We determined the endogenous polyamine content under 1.5 mM Spd and 1.0 mM MGBG(inhibitor of Spd)treatment,and researched chloroplast ultrastructure and ion flux of the 2 chrysanthemum varieties.The main results are as follows:1.Changes of endogenous free polyamine content of salinity stressed chrysanthemum seedlingsChrysanthemum seedlings were cultured in 1/2 Hogland's solution,determined endogenous polymine levels,relative water content and electrolyte leakage rate of 'Qx096'(salt sensitive)and 'Qx097'(salt tolerant)leaf under NaCl stress.The results showed that:the relative water content decreased and electrolyte leakage rate increased after NaCl stress,the endogenous putrescine and spermidine content decreased and spermine content first increased and then decreased.According to previous studies,it is known that spermidine and spermine play protective role on plants,and spermidine is the synthesis precursor of spermine,which essential in alleviating salt stress.Therefore,we select Spd for exogenous addition.2.Protective effects of exogenous Spd on salinity stressed chrysanthemum seedlingsChrysanthemum seedlings were cultured in Hogland's solution,studied the protective effect of 0.5 mM,1.0 mM,1.5 mM,2.0 mM exogenous Spd on growth,photosynthesis,ion balance,osmotic balance and antioxidant systems of salinity-stressed chrysanthemum seedlings.The results showed that:exogenous Spd improved plant growth under NaCl stress,and so did Pn,Gs and Ci.Reduced Na+ accumulation and K+ loss,while increased soluble protein and proline(Pro)content.The improvement of SOD,POD,APX,CAT activities and decrease of malondialdehyde(MDA)by exogenous Spd contributed to clear reactive oxygen species(ROS).Indicated that appropriate concentrations of exogenous Spd can alleviate salinity injury by improving photosynthetic efficiency and ROS scavenging ability,keeping ion balance and osmosis balance of chrysanthemum seedlings.The mitigation effects of 1.5mM were better than the other concentrations of Spd,and its protective capacity was more apparent in 'Qx096' than in 'Qx097'.3.Effects of exogenous Spd on chloroplast structure and ion flux of salnity stressed chrysanthemum seedlingsThis experiment compared the effect of 1.5mM Spd and ImM MGBG(Spd inhibitor)on endogenous polyamine content,chloroplast ultrastructure,ion flux of seedlings leaves.The results showed that:exogenous Spd promoted the accumulation of endogenous Spd and Spm,and decrease of Put;maintained chloroplast structure integrity and increased chlorophyll content,alleviated growth inhibition of salt stress;enhance Na+ efflux of root thereby reducing Na+ content in plants;transferred Ca2+ from the roots to upper leaves,alleviated salt injury of young leaves.It can be concluded that the suitable concentration of exogenous Spd alleviate salt damage of chrysanthemum through protecting the chloroplast structure and maintaining the ion balance.