Mechanism Of Reactive Oxygen Species Metabolism Regulated By G6P DH In Disease Resistance Against Blue Mould Of Apple Fruit After Acibenzolar-S-methyl Treatment

Apple fruit?Golden Delicious?was used as materials to study the effect of 100mg/L acibenzolar-S-methyl?ASM?and different concentrations of DHEA?an inhibitor of G6PDH??50?M,100?M,200?M,400?M?treatment on lesion development of fruit inoculated with Penicillium expansum,G6PDH activity and gene expression,reactive oxygen species?ROS?metabolism and quality during room temperature storage.The main results are as following:1.Compared with the control,100 mg/L ASM treatment significantly inhibited the lesion development of apple fruit inoculated with P.expansum.50?M DHEA combined with ASM treatment did not affect the lesion diameter compared to ASM treatment,while 100?M,200?M and 400?M DHEA combined with ASM promoted the lesion development.Especially,100?M DHEA significantly promoted the development of lesion diameter.2.ASM treatment increased H₂O₂ content,NOX and SOD activities in the flesh and exocarp,as well as the MdSOD expression.ASM+DHEA treatment decreased H₂O₂ content in apple flesh during the early storage period,decreased H₂O₂ content in apple exocarp,inhibited the activities of NOX and SOD as well as the expression of MdSOD in apple flesh and exocarp.3.ASM treatment inhibited CAT activity in flesh,but promoted CAT activity in exocarp,and enhanced the activities of POD,GR,MDHAR and DHAR both in the flesh and exocarp.More,ASM treatment increased expression of MdAPX and MdDHAR,decreased MdMDHAR expression and promoted the accumulation of AsA and GSH in flesh and exocarp.ASM+DHEA treatment eliminated the inhibition effect of ASM on CAT activity in apple flesh,inhibited CAT activity in apple exocarp.ASM+DHEA treatment decreased the activities of POD,GR,APX,MDHAR and DHAR,down-regulated the expression of MdAPX,down-regulated MdDHAR expression in apple flesh and MdDHAR expression at 8 d and 10 d in apple exocarp.ASM+DHEA treatment up-regulated MdMDHAR expression in apple flesh,but down-regulated MdMDHAR expression in apple exocarp and decreased the content of AsA and GSH.4.ASM treatment enhanced G6PDH activity and NADPH content in the flesh and exocarp,up-regulated the expression of MdG6PDH3,MdG6PDH4 and MdG6PDH6 in apple flesh and MdG6PDH4 expression at 4,6 and 10 d in apple exocarp.ASM+DHEA treatment decreased G6PDH activity and NADPH content,but up-regulated expression of MdG6PDH3 and MdG6PDH6 as well as expression of MdG6PDH4 during the early storage period.ASM+DHEA treatment up-regulated MdG6PDH6 expression and down-regulated MdG6PDH3 expression at 2,8,10 d compared with the ASM-treated apple exocarp.5.The results of immunofluorescence showed that ASM treatment significantly promoted the accumulation of G6PDH protein at 6 d in apple flesh,however,ASM+DHEA treatment decreased the accumulation of G6PDH protein.6.ASM treatment did not change the weight loss of apple fruit,but delayed the decline of flesh firmness,inhibited the respiratory intensity and ethylene release,also decreased titratable acid?TA?content and increased total soluble solids?TSS?content in apple fruit.ASM+DHEA treatment delayed weight loss of apple fruit,but accelerated the decline of flesh firmness,increased TA content,decreased TSS content.ASM+DHEA also enhanced respiratory intensity and ethylene release and advanced respiratory peak and ethylene peak.In conclusion,ASM treatment enhanced MdG6PDH expression and G6PDH activity as well as protein accumulation,increased NADPH content,activated ROS metabolism and enhanced disease resistance against blue mould of apple fruit,and kept good quality.However,ASM+DHEA treatment decreased G6PDH protein accumulation and G6PDH activity,inhibited the accumulation of NADPH and ROS metabolism,decreased disease resistance against blue mould and changed some quality of apple fruit.All these results suggest that ROS metabolism regulated by G6PDH play important role in disease resistance against blue mould of apple fruit after ASM treatment.