Effects Of Exogenous Spermidine On Leave Proteomics And Antioxidant System In Tomato Seedlings Under High Temperature Stress

High temperature is one of the major abiotic stresses,affecting the physiological and biochemical processes of plants directly,altering the growth patterns of plants indirectly,and affecting seedlings morphogenesis.Tomato(Lycopersicon esculentum Miller)is one of the main type of vegetable crops in protected cultivation,which is vulnerable to high temperature stress,especially in spring,summer and autumn greenhouse planting.Polyamines(PAs)are kinds of low molecular weight and ubiquitous nitrogenous compounds,mainly including putrescine(Put),spermidine(Spd)and spermine(Spm),participating in the regulation of plant growth and responsing to abiotic stress.In the present study,we used heat-sensitive tomato cultivar(cv.Puhong 968)as the test material,to study the effects of exogenous spermidine(1 mM Spd)on proteomics and antioxidant system in tomato seedlings under the high temperature stress(38/28 ?,day/night),to investigate the physiological and molecular mechanism of how exogenous Spd improved the high temperature resitance of tomato seedlings.The main results are as follows:1.Exogenous Spd significantly alleviated the inhibition of growth induced by the high temperature stress.A two-dimensional gel electrophoresis(2-DE)coupled with matrix-assisted laser desorption/ionization tandem time of flight mass spectrometry(MALDI-TOF/TOF-MS)were performed.A total of 67 differentially accumulated protein spots were confidently identified in response to high temperature stress and/or exogenous Spd.The resulting proteins involved in photosynthesis,cell rescue and defense,amino acid metabolism,protein synthesis,folding and degradation,energy and metabolism,and signal transduction.Exogenous Spd up-regulated most identified proteins involved in photosynthesis,rescue defense and energy metabolism,implying an enhancement in photosynthetic and antioxidant defense capacity.These results suggested that exogenous Spd can regulate the protein expression level of tomato leaves under high temperature stress,then enhance the high temperature tolerance,and promote the growth of tomato seedlings.2.Under high temperature stress,the levels of ROS(including O2·-and H2O2)in tomato leaves were significantly increased,causing membrane lipid peroxidation damage.Application of exogenous 1 mM Spd significantly increased the activities of antioxidant enzymes and regulated the gene expression of the antioxidant enzymes.Moreover,exogenous Spd also increased the content of non-enzymatic antioxidants(AsA and GSH),maintaining the intracellular redox balance,alleviating the lipid peroxidation induced by the high temperature stress.These results suggested that exogenous Spd can significantly activate the antioxidant enzymes and non-antioxidant antioxidants,reduce O2·-generation rate and the content of H2O2 and MDA,alleviate the oxidative damage of tomato seedlings caused by high temperature stress and decrease membrane lipid peroxidation.3.In order to further explore the antioxidant tolerance induced by exogenous Spd under high temperature stress,the effects of mitogen-activated protein kinase(MAPK)cascade pathway induced by exogenous Spd were studied under high temperature stress.The MAPK cascade pathway inhibitor PD98059 was used to study the role of the MAPK cascade pathway in Spd induced antioxidant system.The results showed that exogenous Spd could alleviate the oxidative damage caused by high temperature stress through improving the activity of antioxidant enzymes and the expression of the related genes.The use of MAPK inhibitor PD98059(10 ? mol·L-1)significantly increased the oxidative damage,and inhibited Spd-induced antioxidant enzyme activity and related gene expression.These results indicated that MAPK was involved in exogenous Spd-induced antioxidant protection process,which may be related to the high temperature tolerance induced by exogenous Spd.