Study On The Correlationship Between Chloroplast PsbA Gene Expression And PSⅡ Repair Of Wheat Under High Temperature Stress And Exogenous Regulation

Wheat （Tritivum aestivum, L） is the second food crop in China, also is themain food crops in northern China, and its yield impacts not only people’s livingstandards but also national economic development directly. In recent years, with theincreasing change of global climate, the high temperature stress has become one ofthe most vulnerably adverse factors during wheat growth process. High temperaturestress could damage wheat photosynthetic apparatus, reduced photosynthetic function,hinder seed growth, and cause serious yield reduction as a result. The D1proteinencoded by psbA gene is an important part of wheat photosynthetic apparatus, and hasbeen proved to be closely associated with wheat resistance to high temperature stress.Therefore, this article studied the wheat chloroplast psbA genes expressioncharacteristics,chlorophyll fluorescence parameters, photosynthetic rate, antioxidantenzyme activity and the stability of cell membrane under high temperature stress.Meanwhile, the regulation effects of exogenous salicylic acid （SA） and glycinebetaine（GB） on the psbA expression were also studied to reveal its correlationship with PSⅡfunction repair under high temperature stress, which was in order to further clarify therepair mechanism of heatd amaged photosynthetic apparatus, and provide scientificbasis for the development of resilience strain technology.Two wheat variety “Aikang58and Yumai49” as materials, the experiments werecarried out on the experimental farm of Henan Agricultual University. Wheat seedswere planted in pots. Foliar sprayings3days （1time one day） of distilled water,0.1mmol·L^-1SA,0.3mmol·L^-1SA,0.5mmol·L^-1SA,0.1mmol·L^-1GB,1.0mmol·L^-1GBand10mmol·L^-1GB were treated during grain filling stage （the20th day afteranthesis）. Then the plants were exposed to irradiance of2000μmol·m^-2·s^-1providedby1000W tungsten lamp and temperature of40℃for2h, recovery3hprocessing(25℃，PFD：600umol·m^-2·s^-1). Respectively sampling before and after the stress, stress recovery on the flag leaves by the treatment as test materials were usedto measure physiological and biochemical characteristics, and psbA genes expressionas well. The main results were as follows:1. The effect of high temperature stress on wheat chloroplast psbA expression andexogenous SA and GB regulationsPlant photosystem Ⅱ （PSⅡ） is a key part of the stress-induced injury, the D1protein not only is a subunit of the PSⅡ multi-subunit complex, but also is the originaltarget under stress damage. Therefore, the crucial step of PSⅡ repair is thedegradation of injured D1protein and replaced by the newly synthesized copies,which is encoded by psbA gene. The results of present study showed that wheatchloroplast psbA gene expression was suppressed under high temperature stress.Compared with the control （water treatment）, different concentrations of SA and GBtreatment improved psbA gene expression under high temperature stress and recoveryperiod, and enhanced the damaged D1protein synthesis under the stress, therebyslowing the adversity of wheat photoinhibition, protecting the reaction center ofphotosystem Ⅱ （PSⅡ） to maintain the normal operation of the plant photosyntheticapparatus.2. The effect of high temperature stress on wheat chloroplast PSⅡ functionand SA andGB exogenous regulationsThe wheat chloroplast PSⅡ primary photochemical efficiency （Fv/Fm）, PSⅡpotential activity （Fv/Fo）, thylakoid physical fitness of the inherent efficiency of PSⅡ（Fv′/Fm′）, actual photochemical efficiency （ΦPSⅡ）, photochemical sudden quenchingcoefficient （qP）, the ETR （PSⅡ electron transport rate） and net photosynthetic rate （P_n）significantly reduced under high temperature stress. Compared with the control （watertreatment）, Fv/Fm, Fv/Fo, Fv′/Fm′, ΦPSⅡ, qP, ETR and P_nslowly down reducedunder high temperature stress and recovery period by SA and GB treatment, therebyreducing the extent of the damage of the photosynthetic apparatus to maintain thestability of the structure of PSⅡ reaction centers and normal turnover rate.3. The effects of high temperature stress on wheat chloroplast antioxidant enzymeactivities and cell membrane stabilityand exogenous SA and GB regulationsWheat cell membrane stability lessensand membrane fluidity increases underhigh temperature stress. The activities of antioxidant enzyme catalase （CAT） andperoxidase （POD） both decreased while the MDA’s accumulation and superoxidedismutase （SOD） activity increased. Compared with the control （water treatment）, SOD, CAT and POD activities improved under high temperature stress and recoveryperiod by SA and GB treatment, slowed down the accumulation of MDA, enhancedthe stability of the membrane.4. The effect of high temperature stress on wheat leaves osmoregulation substance andexogenous SA and GB regulationsPlant stress resistance is closely related with body substances free praline.Proline is very sensitive to stress, proline content can rapidly accumulate in wheatleaves under high temperature stress. The foliar application of SA and GB increasedpraline contents that played an important role in osmotic adjustment in wheat leavesunder high temperature stress. At the subsequent recovery stage, exogenous SA andGB treatment can effectively inhibit the reduction of proline content and enhance theability of the wheat resistance to high temperature stress.