Effects And Mechanism Of Prohexadione-calcium On Alleviating Salt Stress In Rice At The Seedling Stage

With the global warming,salt stress has become an important abiotic stress that seriously threatens growth and development of plants.Prohexadione-calcium（Pro-Ca）,as a delayed plant growth regulator,can improve the stress resistance of plants when they are stimulated by the outside world.Rice is the primary food crop in China.Understanding its stress resistance mechanism and exploring its stress resistance measures can promote the development of rice industry.In this experiment,the regulation of Pro-Ca on rice under salt stress was studied.Pot experiment was conducted with different rice varieties IR29 and HD96-1 as materials in greenhouse.Pro-Ca or salt treatment was carried out in 1.5-leaf stage of rice.Using morphological,physiological and transcriptome techniques to explore the mechanism of Pro-Ca in alleviating salt stress in rice seedlings.The main findings are as follows:1.Salt stress inhibited the growth and development of rice seedlings on the ground and roots,hindered the accumulation of rice biomass,and reduced the plumpness and strong seedling index of rice seedlings.Pro-Ca further reduced the plant height of rice,and the plant height of HD96-1 decreased most significantly.Under salt stress,Pro-Ca promoted the widening of rice stem base width,the increase of leaf area,the growth of root system and the accumulation of biomass,and finally made the seedlings full and strong seedling index increased.Finally,the salt tolerance index of IR29 rice in the two periods was increased by 20.51%and 15.17%,and HD96-1 rice in the two periods was increased by 30.26%and 20.95%,respectively.2.Transcriptome data analysis showed that 331 differentially expressed genes and 224differentially expressed genes were detected in CK vs S comparison group.In CK vs S+Pro-Ca comparison group,197 differentially expressed genes and 304 differentially expressed genes were detected.Among them,there are 75 significantly down-regulated genes in the differentially expressed genes that only respond to salt stress,and 97 significantly up-regulated genes in the differentially expressed genes that only respond to Pro-Ca regulation.KEGG pathway analysis and GO analysis of these genes showed that under salt stress,rice down-regulated photosynthesis,potassium ion transport,sodium and potassium proton antiporter activity,MAPK signal transduction pathway and related genes of salt-tolerant transcription factors family such as ERF,NAC,MYB and WRKY.However,after exogenous Pro-Ca,these genes were no longer induced by salt stress,but on the contrary,they were up-regulated in chloroplast,photoresponse repair,photosynthetic electron transport in photosystem I and related genes of salt-tolerant transcription factor family such as ERF,WRKY and b HLH.3.Salt stress hindered the photosynthesis of rice.Pro-Ca alleviated the degradation of photosynthetic pigments in leaves of IR29 and HD96-1 under salt stress,increased the content of photosynthetic pigments（Chla,Chlb and Car）,increased the photosynthetic gas exchange parameters（T_r,C_i,G_s）of rice,and increased the maximum photochemical efficiency（F_v/F_m）and potential activity（F_v/F_o）of photosystem II.Finally,the net photosynthetic rate（P_n）of IR29rice in the two periods was increased by 40.13%and 9.26%,and the P_nof HD96-1 rice in the two periods was increased by 22.23%and 17.55%,respectively.4.Salt stress destroyed the ROS metabolism balance of rice leaves,promoted the increase of O₂^·-and H₂O₂,accelerated the process of membrane lipid peroxidation,and led to the significant increase of MDA content and EL.At the same time,salt stress destroyed the antioxidant system of rice,and decreased the activities of SOD,POD,CAT,APX and the contents of As A and GSH.Pro-Ca increased the activity of antioxidant enzymes and the content of non-enzymatic antioxidant substances in rice leaves of IR29 and HD96-1,and effectively inhibited the increase of MDA,H₂O₂ and O₂^·-.The EL of the two periods of IR29 rice decreased by 16.32%and 2.53%,and the EL of HD96-1 rice in the two periods decreased by 6.75%and23.31%,respectively.5.Salt stress destroyed the Na⁺and K⁺homeostasis in the aboveground and underground parts of rice,and reduced the soluble protein content in rice leaves.Pro-Ca increased the soluble protein content of rice,decreased the Na⁺content and increased the K⁺content in the aboveground and underground parts of rice.The ratio of Na⁺and K⁺in the aboveground and underground parts of IR29 rice decreased by 87.3%and 85.87%,and the ratio of Na⁺and K⁺in HD96-1 rice decreased by 92.6%and 76.41%,respectively.Pro-Ca effectively alleviated the damage of salt stress on ion homeostasis and osmotic adjustment of IR29 and HD96-1.All in all,salt stress inhibited the photosynthetic rate of rice seedlings,broke ion homeostasis,aggravated membrane lipid peroxidation,and affected the normal growth and development of rice seedlings.Pro-Ca increased the photosynthetic pigment content and enhanced the photosynthesis of rice by up-regulating the genes related to photosynthesis.By increasing the activity of antioxidant enzymes and the content of non-enzymatic antioxidants,the oxidative stress and membrane lipid peroxidation were reduced.The soluble protein content was increased,and the osmotic adjustment ability of rice was improved.Up-regulated genes related to cell ion homeostasis,decreased Na⁺content,increased K⁺content and maintained cell ion homeostasis.Finally,Pro-Ca enhanced the ability of IR29 and HD96-1 rice to resist salt stress,and promoted the normal growth and development of rice under salt stress.