| In the actual production of China,many important horticultural crops sensitive to low temperature [such as tomato(Solanum lycopersicum L.)] often suffer from sub-low temperature stress due to the cold in Winter and cold Spring,which affects the growth and development of crops and the formation of yield.Therefore,it is urgent to find new ideas and develop new methods to resist sub-low temperature stress.Studies have shown that exogenous 5-amino levulinic acid(ALA)can enhance tomato for low temperature tolerance,but the specific mechanism has not yet clear,therefore,in this study,low temperature sensitive tomato variety ‘Jinpeng NO.1’ choosen as test materials,to explore the effect of exogenous ALA on the photoinhibition protective and mineral nutrient absorption and transshipment in tomato seedling grown in the sub-low temperature stress,in order to enrich the mechanism of ALA in plant abiotic stress.The main results are as follows: tomato under the sub-low temperature stress of1.Exogenous ALA enhanced the xanthophyll cycle of tomato seedlings under sub-low temperature stress,and alleviated the damage of sub-low temperature stress on photosystem Ⅱ(PSⅡ)and photosystem Ⅰ(PSⅠ)of tomato seedling leaves.Under sub-low temperature stress,actual quantum yield of PSⅡ [Y(Ⅱ)],maximum photochemical quantum yield of PSⅡ(Fv/Fm),PSII relative electron transfer rate [ETR(Ⅱ)],PSI effective photochemical quantum yield [Y(Ⅰ)],PSI relative electron transfer rate [ETR(Ⅰ)] and PSI maximum photooxidation state P700 content(Pm)of tomato seedling leaves were all inhibited,while non-photochemical quenching(NPQ)and non-photochemical quenching coefficient(qN)were all increased.Exogenous application of ALA significantly increased Y(Ⅱ),Fv/Fm,ETR(Ⅱ),Y(Ⅰ),ETR(Ⅰ)and Pm of tomato seedling leaves,and significantly alleviated the photoinhibition of PSII and PSI.Sub-low temperature stress increased the contents of zeaxanthin(Z)and xanthophyll cycle library(V+A+Z),increased the rate of deepoxidation[(A+Z)/(V+A+Z)],upregulated the expression of PSII CP43 chlorophyll decoprotein gene(psbC),D2 protein gene(psbD),rubose 1,5-bisphosphate carboxylase(RuBP)large subunit gene(rbcL),RuBP small subunit gene(rbcS),and inhibited the expression of violaxanthinde-epoxidase gene(VDE)and zeaxanthin epoxidase gene(ZE)genes.Exogenous application of ALA further significantly increased the contents of Z and V+A+Z,and increased(A+Z)/(V+A+Z)under sub-low temperature,and significantly downregulated the expression of psbC,psbD,rbcL and rbcS genes,and significantly upregulated the expression of VDE and ZE genes.These results indicate that,under the sub-low temperature stress,exogenous ALA can protect PSII and PSI from photoinhibition by enhancing the lutein cycle,so as to alleviate cold damage to the seedling photosynthetic mechanism and inhibition of electron transfer,and enhance low temperature resistance of the seedlings,and maintain the non photochemical quenching,photochemical quenching and the balance of heat dissipation of energy dissipation of three ways,it promotes the transfer of light energy to the photosynthate by photochemical quenching at low temperature.2.Exogenous ALA relieved the stress of sub-low temperature on tomato seedling root growth and structure.Sub-low temperature stress can damage the root structure of tomato seedlings,and reduce the root activity,catalase(CAT)activity and the content of osmotic regulatory substances.However,exogenous ALA can eliminate the adverse effects of sub-low temperature on root structure,significantly improve the total root length,root surface area and root volume of tomato seedlings,promote the occurrence of root tip number and root branch number,significantly improve the root activity of tomato seedlings under sub-low temperature stress,and reduce the content of malondialdehyde in roots and root relative electrical conductivity.Meanwhile,superoxide dismutase activity,CAT activity and proline content were significantly increased.In conclusion,pre-spraying ALA under sub-low temperature can improve root activity,enhance antioxidant enzyme activity in roots,and increase the content of osmotic regulatory substances in roots,thus reducing the damage of reactive oxygen species caused by sub-low temperature stress to tomato seedling root cells,and effectively alleviating the inhibition of sub-low temperature stress on tomato seedling root growth,increase tomato seedling root of sub-low temperature resistance.3.Exogenous ALA can alleviate the inhibition of sub-low temperature on element transport and distribution in tomato seedlings.Under sub-low temperature stress,the contents of dry matter in new leaves,old leaves,roots and stems decreased significantly,and the root was the most severely inhibited,and the transport of N,P,K,Fe,Mg and Ca to the shoots(especially the tender parts of leaves)was blocked.In the sub-low temperature stress before spraying exogenous ALA,inhibition of the growth of tomato seedling leaves grow condition was significantly reduced,and the ground part(new leaves,old leaves and stems)N content,the leaf P content,plant K content of whole,integrated content of Fe,Mg content,root Mg content and leaf Ca content increased significantly,improve the allocation rate of P and K in new leaves,the distribution of N in old leaves was decreased,the distribution of Fe,Mg and Ca in leaves was significantly increased,and the distribution of Fe,Mg and Ca in roots and stems was significantly decreased.To sum up,under sub-low temperature stress,exogenous spraying ALA beforehand by starting xanthophyll cycle to the tomato leaf PSI and PSII photoinhibition protection,and by enhancing the tomato root of antioxidant enzyme system and improving the osmotic regulation substances content in easing the sub-low temperature stress on tomato seedling root structure damage and inhibition of root growth,it promote the absorption and transport of nutrient elements to the aboveground part of tomato seedlings under sub-low temperature stress. |
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