Studies On Action Mechanism Of Delaying Senescence And Improving Disease-resistance In Harvested Anxi Persimmon Fruits By 1-MCP Treatment

Anxi persimmon(Diospyros kaki L.cv.Anxi)is a chief and distinguished cultivar in South China,which has thin peels,soft texture,elegant flavour and high nutritional value.But the harvested fruits are easy to deteriorate,such as softening and decay during storage time,which reduce the appearance quality and nutritional value,bringing great difficulties to its long-term storage and long-distance transportation.The previous studies have shown that,1.35 ?L·L-1 of 1-MCP treatment had significant effects on retarding ripening and senescence of Anxi persimmon,but its mechanism is for further reasearch.Anxi persimmon(Diospyros kaki L.cv.Anxi)fruits were treated with AnsiP-STM(a new anti-ethylene product)for 12 hours at room temperature and then stored in the condition of(25±1)? 85%relative humidity.The objective of this research was to clarify the action mechanism of 1-MCP treatment for delaying senescence and improving disease-resistance of harvested Anxi persimmon fruits by investigating tissue energy metabolism and membrane lipid metabolism related to fruit senescence,and the changes of activities of disease defense-related enzymes related to disease-resistance of fruit.The rusults were showed as follows:The treatment of 1.35 ?L-L"1 of 1-MCP inhibited the decrease of ATP content and energy charge level,and maintained relatively higher activities of cytochrome c oxidase(CCO)and H+-ATPase,Ca2+-ATPase,Mg2+-ATPase at the late stage of Anxi persimmon fruit storage.Meanwhile,Anxi persimmon fruit treated with 1-MCP kept higher activity of NAD kinase(NADK),higher content of NADP(H),and delayed accumulation of NAD(H).From the results,it could be concluded that 1-MCP treatment maintained energy status to meet the energy requirments of the normol metabolism in Anxi persimmon fruit,and inhibited the losing of ion balance inside and outside of cells,along with the function of cell membrane on choosing,thus retarding the process of fruit senescence.The treatment of 1.35 ?L·L-1 of 1-MCP inhibited activities of phospholipase D(PLD),lipase and lipoxygenase(LOX),and maintained higher relative contents of unsaturated fatty acids,such as palmitoleic acid,oleic acid,linoleic acid,linolenic acid,along with lower relative contents of saturated fatty acids,such as palmitic acid,stearic acid.Thus,1-MCP treatment retarded the index of unsaturated fatty acids(IUFA)and unsaturated degree of fatty acids,and inhibited accumulation of malondialdehyde(MDA)content.From the results,it could be concluded that 1-MCP treatment decreased activities of membrane lipid-degrading enzymes,and reduced the degradation of unsaturated fatty acids of membrane lipids and maintained higher unsaturated degree of fatty acids,resulting in increasing the liquidity of membrane and maintaining integrity of cell membrane structure.The treatment of 1.35 ?L·L-1 of 1-MCP increased activities of chitinase(CHI),(3-1,3-glucanase(GLU),and induced the activities of disease defense-related enzymes,such as phenylalanine ammonialyase(PAL),polyphenoloxidase(PPO)and peroxidase(POD),thus increasing the accumulation of lignin and total phenolic,and significantly inhibited decay incidence of Anxi persimmon fruits.From the results,1-MCP treatment increased activities of disease defense-related enzymes and contents of disease defense-related material,which might account for improved disease resistance and lower decay incidence of fruits.