The Regulation Effect Of Exogenous Spermidine On The Resistance Of Tomato Seedlings Under Isotonic Salt Stress

Taking the cultivar of salt sensitive type as materials（‘Zhongza 9’）,hydroponic method was carried out,150 mmol/L NaCl and 100 mmol/L Ca（NO₃）₂ were used to simulate isotonic saline stress environment,the effects of exogenous 0.25 mmol·L-1 Spd（foliar spraying）on the plant growth,photosynthetic characteristics,water metabolism,antioxidant system and osmotic regulation system were investigated to explore the the physiological regulation mechanism of exogenous Spd on improving the salt resistance of tomato seedlings under isotonic salt stress.The main results are as follows:1.Under isotonic NaCl and Ca（NO₃）₂ stress,the growth of tomato seedlings was inhibited,and the inhibition of NaCl stress on tomato seedlings was significantly greater than that of Ca（NO₃）₂ stress.The net photosynthetic rate,stomatal conductance and transpiration rate were all significantly reduced under isotonic salt stress,and the decrease of Ca（NO₃）₂ stress was smaller.Under NaCl stress,the concentration of intercellular CO₂ in tomato seedlings increased significantly,root activity,the content of photosynthetic pigments（chlorophyll and carotenoid）,water use efficiency and stomatal limitation index decreased significantly,however the intercellular CO₂ concentration of tomato seedlings decreased significantly,and root activity,the content of photosynthetic pigments and stomatal limitation index increased significantly under Ca（NO₃）₂ stress.The identification degree and boundary definition of the leaves and main veins of tomato seedlings under Ca（NO₃）₂ stress were better than NaCl stress,and the arrangement of leaf tissues under NaCl stress was more disorderly than Ca（NO₃）₂ stress.Under isotonic NaCl and Ca（NO₃）₂ stress conditions,exogenous Spd could significantly improve the growth,leaf photosynthetic pigment content,leaf net photosynthetic rate,stomatal conductance and transpiration rate of tomato seedlings,as well as the stomatal and non-stomatal limitation,caused by isotonic NaCl and Ca（NO₃）₂ stress,could be alleviated by exogenous Spd.The identification degree and boundary definition of the leaves and the main veins of tomato seedlings under isotonic NaCl and Ca（NO₃）₂ stress were improved.2.Under isotonic NaCl and Ca（NO₃）₂ stress,the leaf relative water content,water content,water potential,root hydraulic conductance,total root length,total surface area,total volume and average diameter were significantly decreased of tomato seedlings,and the decrease of Ca（NO₃）₂ stress was smaller.Exogenous Spd could alleviate the decreases in leaf relative water content,water content,water potential,root hydraulic conductance and total root length,total surface area,and exogenous Spd enhanced the hydraulic conducantance and water absorption ability of roots,therefore improving the water condition of tomato plants.3.Under isotonic NaCl and Ca（NO₃）₂ stress,the antioxidant enzyme activity of tomato seedlings decreased significantly,and the decrease of Ca（NO₃）₂ stress was smaller,the relative permeability of plasma membrane,MDA,O₂ˉ.and H₂O₂ content were significantly increased,and the oxidative damage of Ca（NO₃）₂ stress on tomato seedlings was less than that of NaCl stress.But spraying a certain concentration of exogenous Spd could increase the antioxidant enzyme activity and reduce the relative permeability of plasma membrane,MDA,O₂^ˉ.and H₂O₂ content of tomato seedlings under isotonic NaCl and Ca（NO₃）₂ stress,also could alleviate the damage caused by salt stress of tomato seedlings and enhance its salt resistance.4.Under isotonic NaCl and Ca（NO₃）₂ stress,the content of soluble sugar,free amino acid,proline and organic acid of tomato seedlings increased significantly,and the increase of Ca（NO₃）₂ stress is greater,the content of soluble protein and osmotic potential decreased significantly,and the damage degree of Ca（NO₃）₂ stress on the osmotic regulation system of tomato seedlings was smaller.However exogenous Spd increased the osmotic substance content and osmotic potential of tomato seedlings under isotonic NaCl and Ca（NO₃）₂ stress,and improved the salt resistance of tomato seedlings.But it is a complicated process to regulate the salt resistance of tomato seedlings by exogenous Spd under isotonic NaCl and Ca（NO₃）₂ stress,and the research needs to be further studied.