Analysis Of The Effect Of ABA On Alleviating Low Temperature-Induced Photosynthetic Disturbance Of Tomato Leaves

Tomato（Solanum lycopersicum L.）is a widely cultivated crop that also plays a very important role in the economy.It is very sensitive to a series of abiotic stresses,especially extreme temperatures.Low temperature seriously affects the growth and development of plants,among which photosynthesis is the first affected process.Abscisic acid（ABA）is a commonly used plant hormone.It regulates various physiological processes from stomata opening to protein storage,and adapts to various stresses.Here,we use the ABA deletion mutant sit and its wild-type RR as test materials,carry out exogenous ABA pretreatment and normal temperature（25/15℃）and low temperature（4℃）treatments for 24 h to explore the mechanism of low temperature stress leading to tomato photoinhibition and the mechanism of ABA alleviating the photoinhibition of low temperature stress.The main findings are as follows:1.It is clear that ABA alleviates the photosynthesis of tomato leaves under low temperature.The research results show that under low temperature stress,the net photosynthetic rate（Pn）,intercellular CO₂ concentration（Ci）,transpiration rate（Tr）and stomatal conductance（Gs）of sit at low temperature（SLT）are lower than RR at low temperature（RLT）,and the above indicators of sit at low temperature after exogenous spraying of ABA（SAL）are higher than SLT,indicating ABA can improve the photosynthetic capacity of tomato leaves under low temperature stress.In addition,under low temperature stress,SLT’s chloroplast width,area and number of osmiophilic granules were significantly larger than RLT,and chloroplast length/width was significantly smaller than RLT.Exogenous ABA pretreatment significantly alleviated the above phenomenon,indicating that ABA can maintain the chloroplast structure and relieve damage caused by low temperature stress.2.It is clear that ABA alleviates the photochemical activity of PSII in tomato leaves under low temperature stress.The research results show that under low temperature stress,the PSII maximum photochemical efficiency（Fv/Fm）,PSII actual photochemical quantum efficiency[Y（II）],PSII relative electron transfer rate[ETR（II）],non-photochemical quenching（NPQ）,PSII’s quantum yield[Y（NPQ）]for regulated energy dissipation of SLT is lower than RLT,while the non-regulated energy dissipation in PSII[Y（NO）]and PSII excitation pressure（1-q P）performance show opposite trends,indicates that the lack of ABA under low temperature stress further reduces the photochemical efficiency of PSII and closes the PSII reaction center.Exogenous ABA pretreatment reduces the degree of change of the above parameters to varying degrees and alleviates the photoinhibition of PSII.In addition,ABA can significantly up-regulate the expression of Psb A（D1）,Psb B（CP47）,Psb C（CP43）and Psb D（D2）genes,indicating that ABA can maintain the photochemical activity of PSII by promoting the expression of PSII complex protein transcription levels.3.It is clear that ABA alleviates the photochemical activity of PSI in tomato leaves under low temperature stress.The results show that the effective quantum yield of PSI photochemistry[Y（I）],the electron flow through PSI[ETR（I）]and the quantum yield of PSI non-photochemical energy dissipation due to acceptor-side limitation[Y（NA）]of SLT are lower than RLT under low temperature stress.The quantum yield of PSI non-photochemical energy dissipation due to donor-side limitation[Y（ND）]of SLT is higher than RLT,indicating that the lack of ABA further reduces the photochemical efficiency of PSI and the limitation on the donor side.The exogenous ABA pretreatment reduces the degree of changes in the above parameters to varying degrees and alleviates the photoinhibition of PSI.In addition,ABA can significantly up-regulated the expression of Psa A and Psa B genes,indicating that ABA can maintain the photochemical activity of PSI by promoting the expression of PSI complex protein transcription levels.4.It is clear that ABA contributes to the production of proton power and the balance of ATP/NADPH in tomato leaves under low temperature stress.The results showed that theΔp H of SLT was lower than RLT andΔψof SLT was higher than RLT,theΔp H of SAL was higher than SLT andΔψof SAL was lower than SLT under low temperature.In addition,monitoring of the P515 signaling found that the thylakoid membrane in SLT was severely damaged and the ATPase activity was significantly inhibited compared with RLT after low temperature stress.Exogenous ABA pretreatment alleviated this phenomenon,indicating that ABA can generate proton dynamic potential by adjustingΔp H/Δψ,increase the activity of ATPase to maintain the balance of ATP/NADPH,and thereby alleviate the damage caused by low temperature stress.5.It is clear that ABA can promote cyclic electron flow in tomato leaves under low temperature stress.The research results show that cyclic electron flow quantum yield[Y（CEF）]and cyclic electron flow rate[ETR（CEF）]of SLT are lower than RLT under low temperature stress,while Y（CEF）and ETR（CEF）of SAL is higher than SLT,indicating that ABA can alleviate the photoinhibition by improving the operation of cyclic electron flow under low temperature stress.In addition,ABA can significantly up-regulate the expression of NDHB1,NDHB2,NDHB3,NDHC1,NDHL1,NDHL3,NDHM,NDHOX1,NDHOX2 and PGR5 genes,indicating that ABA can play a photoprotective effect through two circular electron flow pathways of PGR5 and NDH.6.It is clear that ABA alleviates the transcriptomic characteristics of photoinhibition of tomato leaves under low temperature stress.In this study,15 c DNA libraries were constructed and 9110 differentially expressed genes（DEG）were detected.Then the GO and KEGG enrichment analysis was performed on DEG,and it was found that photosynthesis,plant hormone signaling transduction,and primary and secondary metabolism-related pathways were more enriched.Among them,the DEG in the plant hormone signaling transduction pathway is mainly concentrated in the ABA signaling transduction pathway and the auxin signaling transduction pathway.ABA can up-regulate significantly the expression of PP2C,AUX1,ARF and SAUR genes.Differentially expressed genes in the photosynthesis pathway are concentrated in PSII and PSI.ABA can significantly up-regulate the expression of PSII and PSI-related genes.Among them,Psb A（D1）in PSII and NDH-related genes in cyclic electron flow have the most significant changes.In addition,ABA regulates 295 transcription factors,such as members of b HLH and NAC related families.Finally,the expression of 10genes was evaluated by q RT-PCR,confirming the reliability of transcriptome analysis.