Alleviation Mechanism Of Exogenous Calcium On Thylakoid Membrane Protein And Chlorophyll Metabolism In Tomato Leaves Under Low Light

Vegetable 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.The low light limits the growth and development of vegetables.In recent years,the degree of low light 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.Therefore,it is of great significance to study effects of low light on the photosynthesis,and the regulation in disorders of vegetables growth and development in production under low light to achieve the high yield and high quality cultivation of vegetables.Based on the previous research of our team,the effects of exogenous calcium on thylakoid membrane protein and chlorophyll metabolism gene in tomato(Lycopersicon esculentum Mill,'W')leaves were studied,which provide a theoretical basis of calcium preparation application to production.The main research results are as follows.1.It was clear that exogenous calcium alleviates the decrease of photosynthetic system activity in tomato leaves under low light.The results showed that low light significantly reduced the photosynthetic rate(Pn),PS? maximum quantum yield and electron transport rate[Y(?)and ETR(?)],and the maximum photochemical efficiency Pm,the electron and energy transfer from PSII to PS? intermediates;it significantly increased Y(NPQ),PS?photochemical efficiency[Y(NO)],excitation pressure and PSI donor side quantum efficiency[Y(ND)].It indicated that low light reduces the photochemical efficiency of PS? and PS?,leading to inhibition of photosynthetic system in QA-QB and PSI-Fd.Exogenous calcium significantly increased Pn,Y(?)and ETR(?),Y(?),and reduced the excitation pressure and energy dissipation.It indicated calcium reduced the inhibition of photosynthetic system under low light and significantly improved the photosynthetic efficiency.2.It was clear that exogenous calcium regulated on thylakoid membrane proteins related photosynthesis in tomato leaves under low light.The thylakoid membrane protein complexes and subunits of tomato leaves were identified by BN-PAGE and SDS-PAGE.The results showed that low light significantly induced differences expression in 28 protein subunits of thylakoid membranes in tomato leaves,including 17 proteins of PS? and PS?response centers,cytochrome and ATP subunit.Cab1D(8),Cab1B(9),PsaD(19,20,2,3),PsaC(21),PsbE(23)and PsbD(21)were responsive to low light.Further studies had shown that 17 thylakoid proteins were involved in four physiological and biochemical reactions pathways.They were metabolic pathways 16 proteins,94.1%),photosynthetic pathways(13 proteins,76.5%),oxidative phosphorylation pathways(4 proteins,82.4%)and photosynthetic antennas Protein(2,11.8%).Proteins in photosynthesis in this study include PsbB,PsbC,PsbD,PsbE,PsaA,PsaC,PsaD,PsaL,Peta,ATP-?,ATP-? and ATP-?.There were 16 nodes and 55 lines in the final PPI network.It could predict the function of unidentified proteins in the network.3 It was clear that exogenous calcium regulated on the expression of key genes in chlorophyll synthesis and degradation pathway in tomato leaves under low light.The expression of calcium receptor gene and the gene expression in chlorophyll biosynthesis and degradation were analyzed.The results showed that the concentration of free calcium in the low light was significantly decreased,and the expression of CAM and CDPK was significantly decreased.The relative expression of HEMs,CLHs and PORs was significantly decreased,however,the expression of CLH1 and PPH and PAO were significantly increased.Calcium significantly increased the contents of free calcium,the expression of calmodulin and synthetic metabolic genes,decreased the expression of degradable metabolic genes.It indicates that calcium signaling enhances the expression of chlorophyll synthase in tomato under low light and promotes the synthesis of chlorophyll in tomato leaves and reduces the degradation of chlorophyll.