The Mechanism Of The Interaction Of Brassinostroid And Gibberellin In Regulating Cold Tolerance Of Tomato Fruit

Brassinostroid(BR)and gibberellin(GA)are important endogenous plant hormones,which participate in plant response to biological and abiotic stress.Chilling injury(CI)is a main restricting factor for cold-sensitive fruit and vegetable during storage and transportation.Tomato(Solanum lycopersicum L.)is a mode material as typical cold-sensitive fruit and vegetable.Therefore,it is theoretical and practical to understand the mechanisms of CI and to develop safe,effective and economic methods.This study is conducted to investigate the regulation mechanism of BR and GA in response to low temperature stress of postharvest tomato fruit,which laid a further foundation in perfecting the signal network of resistance to CI postharvest fruit and vegetable and reducing the loss of postharvest fruit and vegetable.Postharvest tomato fruit of the wild type(Solanum lycopersicum L.cv.Money maker)and the mutant gib-3,deficient of GA,at the mature green stage pre-treated with 0.5-mM BR by spraying and stored at 4 ? for 28 days.CI index,cell microstructure,electrolyte leakage,malondialdehyde(MDA)content,the activities of lipoxidase(LOX),phospholipase D(PLD),phospholipase C(PLC),pectin methylesterase(PME),polygalacturonase(PG),superoxidase(SOD),catalase(CAT),glutathione transferase(GST)and phenylalnine ammonialyase(PAL)were detected.Based on these physiological results,the sample at 14 days in all tomato fruit were analyzed by metabonomics and assayed related genes expression.The results are as follows.(1)BR pretreatment can reduce chilling injury(CI),electrolyte leakage rate,malondialdehyde(MDA)levels,and inhibit the activities of lipoxidase(LOX),phospholipase C(PLC)and phospholipase D(PLD),pectin methylesterase(PME)and polygalacturonase(PG),and increased the superoxidase(SOD),catalase(CAT),glutathione transferase(GST)and phenylalnine ammonialyase(PAL)activities in WT and gib-3 tomato fruit,which could alleviate the chilling symptom.On the contrary,GA-deficient tomato fruit aggravated lipid peroxidation and reduced antioxidant ability,leading to increase the sensibility to low temperature.A deficiency in GA synthesis also weakened the cold resistance induced by BR in chilled fruit.(2)The metabolomics results showed that sugars,amino acids,organic acids content increased and fatty acids content decreased in untreated WT compared with untreated gib-3.Furthermore,the levels of sugars,amino acids,organic acids were lower in WT,while sugars,amino acids,organic acids were higher but fatty acids were lower in gib-3 in response to BR pretreatment.By KEGG pathway analysis,these metabolites could participate in galactose metabolism,starch and sucrose metabolism and TCA cycle under chilling stress.In addition,BR can also improve the cold resistance of tomato fruit by regulating fatty acids biosynthesis in gib-3.(3)The expression of sugars,amino acids,organic acids biosynthesis related-genes were down-regulated and fatty acids biosynthesis related-genes were up-regulated in untreated gib-3 compared with untreated WT.BR pretreatment can inhibit the expression level of these genes in WT,while BR treatment can significantly increase the expression of sugars,amino acids,organic acids biosynthesis related-genes and inhibit fatty acid synthesis genes expression.The results showed that BR could regulate these genes of WT and gib-3 in different way.In addition,BR pretreatment can stimulate the expression of cold resistance related genes CB1 F and GA synthesis gene GA3ox1.A deficiency in GA synthesis upregulated GA3ox1 expression but downregulated CBF1 expression which accelerated chilling injury.