Exogenous Calcium Alleviates Peanuts Low Night Temperature Photosynthetic Barriers

Peanuts(Arachis hypogaea)are regarded as major oil and cash crops worldwide,so they play a decisive part in edible oil safety in China.Low temperature is one of the key environmental factors as restrictive to the geographic distribution and production for peanuts.The peanut seedling during spring night encountered the lowest temperature stress throughout the day in cold northern China.Peanuts under low temperature stress often experience slow growth and seedling missing even upon recovery,so this shall severely decrease peanut yield and quality formation.The photosynthesis,as the basis for plant growth and development,is one of the most sensitive processes to low night temperature stress and plant nutrition regulation.Therefore,the necessity to improve photo synthetic capacity for peanuts after low night temperature stress is under urgent consideration in terms of both theoretical research and production practice.The research was based on cold-sensitive peanut cultivar 'Fenghua No.1' as experimental materials.And the appropriate concentration of Ca2+ and Ca2+ inhibitors(EGTA?TFP)selected from preliminary test were applicated to regulate the cold adaptation of peanut.We aim to provide a theoretical basis for the calcium regulation of photosynthesis as well as the alleviation of LNT stress.The main research results are as follows:1.Exogenous calcium pretreatment can improve the dry matter accumulation and regulate the photosynthetic gas exchange parameters under LNT.In our study,compared with that of control,dry matter accumulation,stomatal conductance(Gs),transpiration rate(Tr),intercellular carbon dioxide concentration(Ci),water use efficiency(WUE)and net photosynthetic rate(Pn)decreased significantly under LNT stress,while stomatal limitation(Ls)increased significantly.It was due to the influence of both stomatal factors and non-stomatal factors.Exogenous calcium pretreatment alleviated the decrease of Pn by reducing these parameters to some extent.Whereas,EGTA(calcium chelator)and TFP(CaM antagonist)spraying increased these parameters and it caused further decrease in Pn.2.Exogenous calcium pretreatment can improve the absorption of mineral elements in peanut seedlings under LNT.In this text,LNT stress made the content of N,P,K,Mg2+ and Ca2+ were reduced by 22.2%,40%,17.6%,1.6%,16%,respectively.Exogenous calcium pretreatment elevated these parameters,however,EGTA and TFP pretreatment decreased them.These results indicated that exogenous calcium foliar application promoted the absorption of mineral elements,which provided sufficient raw materials for the formation of photosynthetic pigments and photosynthesis.3.Exogenous calcium pretreatment can balance the distribution of excitation energy between PSII and PSI.The results indicated that LNT stress affected the equilibrium distribution of the excitation energy between PSI and PSII.Excitation energy pressure of PSII(1-qP),excitation energy distribution coefficient of PSII(?)and excitation energy distribution between two-light systems unbalanced deviation coefficient(?/?-1)were increased by 36.5%,12.6%,57%,respectively,while excitation energy distribution coefficient of PSI(a)was reduced by 22.2%.Exogenous calcium pretreatment balanced the light energy distribution and increased the energy for photochemical reaction(P),while EGTA and TFP pretreatment decreased them further.4.Exogenous calcium pretreatment can improve the photosynthetic activity of peanut under LNT.Results showed that the level of cyclic electron flow was significantly stimulated by LNT.The maximum photochemical efficiency(Fv/Fm),quantum efficiency of photochemistry(?PSII),electron transfer rate[ETR(II)]and photochemical quenching(qP)decreased significantly,while the non-photochemical quenching(NPQ)increased significantly.The yield of regulated energy dissipation[Y(NPQ)]and the yield of non-regulated energy dissipation[Y(NO)]both increased.These indicated that LNT stress reduced the photochemical efficiency and the PSII reaction center activity.Compared with that of control,LNT stress induced the increase of I point,the electron flow from PSII to PSI decreased,quantum yield of non-photochemical energy dissipation in PSI due to acceptor side limitation[Y(NA)]had a significant rise.It implys that LNT had cause PSI photo-inhibition.Exogenous calcium pretreatment alleviated the degree of change in the above parameters,thereby alleviated the PSII and PSI photo-inhibition.While EGTA and TFP pretreatment induced K point,and increased J point,which means the oxygen-evolving complex was damaged,and the electron flow from QA to QB were hampered.And this damage couldn't be repaired in the short term.