Alleviation Of Adverse Impacts Of Low Light On Tomato Plants:new Insight Into The Protective Role Of Strigolactones

Tomato production in protected cultivation are carried out in the second half of the year,when there is a long low light period in northern China.Low light(LL)is one of the main limiting factors that negatively affect tomato growth and yield.In recent years,the degree of LL and the number of days increased with more foggy weather.It increased a serious reduction in vegetables crop photosynthetic capacity,restricting the efficient production of vegetable facilities.Techniques of chemical regulation are effective horticultural methods to improve stress resistance.Strigolactones(SLs)are carotenoid-derived plant hormones that mediate plant growth in response to various forms of abiotic stresses,including salinity,drought and nutrient deficiency.However,the role of SLs in low light irradiation(LL)-induced photoinhibition remains poorly understood.Therefore,We investigated the effects of foliage spray of GR24,a synthesized SLs,on tomato seedlings grown under LL stress conditions.The main research results are as following:1.The results showed that LL caused adverse effects on plant growth,significantly suppressed carbon assimilation,blocked photosynthetic electron transport,inhibited both PS ? and PS ?,and notably intensified reactive oxygen species accumulation and lipid peroxidation in tomato seedlings.2.Application of GR24 effectively mitigated the inhibition of plant growth and increased the fresh and dry weight of tomato plants under LL.Additionally,GR24 also reduced the LL stress damage to the photosynthetic apparatus was shown by increased net photosynthetic rate(Pn)and chlorophyll(Chl a,Chl b,Chl a+b)content,more of the absorbed light was used for photochemistry,as shown by an increased maximum photochemical efficiencv of PS?(Fv/Fm)and effective quantum yield of PS? and ?[Y(?)and Y(?)]and a decreased nonregulatory quantum yield of energy dissipation[Y(NO)].the excitation pressure of PS ?(1-qP)and the donor side limitation of PS ?[Y(ND)]under LL.3.Application of GR24 to LL-stressed tomato leaves increased the electron transport rate of PS ? and PS ?[ETR(?)and ETR(?)],the ratio of the quantum yield of cyclic electron flow(CEF)to Y(?)[Y(CEF)/Y(?)],the oxidized plastoquinone(PQ)pool size and the non-photochemical quenching(NPQ)to facilitate the stimulation of CEF and mitigate photoinhibition by dissipation of excessive excitation energy under LL stress.4.GR24 application reduced the contents of malonaldehyde(MDA)and hydrogen peroxide(H2O2)by increasing the activities and gene expression levels of the related enzymes[superoxide dismutase(SOD)and peroxidase(POD)]under LL stress.5.These results suggest that exogenous application of GR24 enhances plant tolerance to LL stress by promoting plant utilization of light energy,which consequently alleviates the photosystem injuries caused by excess light energy and reactive oxygen species,and by further improving the efficiency of carbon fixation to meet the growth needs of tomato and enhancing photosynthesis efficiency to improve plant growth.Our research provides fundamental information for further studies of the molecular mechanism of SLs function in regulating photosynthesis.