The Role Of Spermine In Tomato’s Resistance To Salinity–alkalinity Stress And Signal Transduction

Tomatoes are one of the main economic crops grown in the greenhousees.Soil salinization is one of the main abiotic stresses when tomatoes are planting,and affects tomato growth,yield and quality.Studies have found that exogenous polyamines（PAs）can improve the tolerance of plants to salinity–alkalinity stress,while studies on the tolerance of exogenous prespermine（Spm）to salinity–alkalinity stress of tomato seedlings are rarely reported.Therefore,this article uses“Ailsa Craig”as the tomato material,and sets up spraying Spm or H₂O₂,silencing tomato spermine synthase gene（Sl SPMS）,silencing tomato respiratory burst oxidase homolog 1（Sl RBOH1）and other different experimental treatments.The mechanism and signal pathways of Spm improving tomato salt-alkali stress tolerance were studied.The main results were as follows:1.Exogenous Spm improved the antioxidant enzymes capacity of tomato seedlings under salinity–alkalinity stress,and maintain the homeostasis of Na⁺and K⁺,thereby enhancing the salinity–alkalinity stress tolerance of tomato seedlings.Exogenous Spm increased the superoxide dismutase synthesis gene（Cu/Zn-SOD）,catalase synthesis gene（CAT1）,ascorbate peroxidase synthesis gene（c APX）and glutathione（GR1）in tomato seedling leaves The expression of synthesis gene enhances the activities of superoxide dismutase（SOD）,catalase（CAT）,ascorbate peroxidase（APX）and glutathione reductase（GR）,thereby eliminating excessive endogenous reactive oxygen species（ROS）,and reducing the malondialdehyde（MDA）content and relative conductivity（REC）of tomato leaves,and increasing the maximum photochemical rate of photosystem II（Fv/Fm）.At the same time,exogenous Spm can increase the expression of Na⁺/H⁺transporter genes（NHX1 and NHX2）on the vacuolar membrane,and activate the activity of Na⁺/H⁺transporter（NHX）,and reduce the accumulation of Na⁺in tomato roots,stems and leaves,and promote the accumulation of K⁺in roots,stems and leaves,and increase the relative water content（RWC）of tomato leaves,thereby improving the salinity–alkalinity stress tolerance of tomato seedlings.2.Silencing Sl SPMS weakened the antioxidant capacity of tomato seedlings under salinity–alkalinity stress and destroyed the homeostasis of Na⁺and K⁺.Under salinity–alkalinity stress,Sl SPMS silences the expression of Cu/Zn-SOD,CAT1,c APX and GR1 in tomato seedling leaves and decreases the activity of SOD,CAT,APX and GR,thereby accumulating more ROS and leading to higher MDA content of tomato leaves and REC,and lower Fv/Fm.Under salinity–alkalinity stress,expression levels of NHX1 and NHX2 in Sl SPMS silencing tomato seedling leaves,roots,stems decreased,leading that Na⁺content in leaves increased,and K⁺content in leaves decreased,and RWC decreased,so all of these weakened the ability of tomato seedlings to resist salinity–alkalinity stress.3.H₂O₂ signal is involved in Spm-induced regulation of tomato to resiste salinity–alkalinity stress.Under normal condition,exogenous Spm induced the expression of tomato RBOH1 and increased the content of H₂O₂.Exogenous H₂O₂promoted the expression of Cu/Zn-SOD,CAT1,c APX and GR1,and enhanced the activities of SOD,CAT,APX and GR,and increased Fv/Fm,and reduced MDA content and REC,as well as the accumulation of Na⁺in roots,stems and leaves,thereby maintaining homeostasis of Na⁺and K⁺thereby increaseing the RWC of the leaves.Under salinity–alkalinity stress,the use of dimethylthiourea（H₂O₂ scavenger,DMTU）eliminated the ability of Spm to i increase RWC and reduce MDA content and REC of tomato leaves,and affected the ability of Spm-induced the ability of tomato to resist salinity–alkalinity stress.4.The silencing of Sl RBOH1 weakened the antioxidant capacity of tomato under salinity–alkalinity stress,and destroyed the homeostasis of Na⁺and K⁺.The expression levels of Cu/Zn-SOD,CAT1,c APX and GR1 were decreased in Sl RBOH1silencing tomatoes under salinity–alkalinity stress,which in turn affected the activities of SOD,CAT,APX and GR,leading to increase MDA content and REC.Under salinity–alkalinity stress,the Na⁺content in the roots,stems and leaves of tomato silenced by Sl RBOH1 was increased;and the K⁺content was decreased,resulting in RWC decreasing in leaves.Sl RBOH1 silencing disrupted the ability of Spm to increase the RWC and decrease the MDA content of tomato leaves under salinity–alkalinity stress.