Effect Mechanism Of Preharvest CPPU Treatment On Postharvest Quality And Cell Ultrastructure Of Kiwifruit

Forchlorfenuron?CPPU?is widely used in kiwifruit production,leading to the edible quality,storability and disease resistance of kiwifruit are significantly decreased.In order to investigate the mechanism of CPPU declining fruit quality and accelerating ripening and senescence,providing theoretical basis for the rational use of CPPU in kiwifruit production.The effect of preharvest CPPU treatment on single fruit weight,yield per mu,fruit shape index,malformation rate,and postharvest fruit quality,cell wall degradation,cell ultrastructure,reactive oxygen metabolism in Qinmei and Hayward kiwifruit during cold storage was studied.The concentration of CPPU solution was 0,5,10,20 mg/L respectively.The results are as follows:1.Preharvest CPPU treatment significantly increased the single fruit weight and yield per mu in Qinmei and Hayward kiwifruit,and the increase had a dose-effect relationship with treatment concentration,the greater concentration of CPPU solution,the higher output.The output of Hayward was obviously higher than that of Qinmei.But in the aspect of fruit morphology,the fruit shape index was reduced and the malformation rate was improved with the concentration uptake.Furthemore,CPPU treatment had a great negative effect on the nutritional quality of fruit with the increase of treatment concentration,such as SSC,TA,VC,chlorophyll content,etc,and the fruit quality became worse.Dramatically negative effect of10,20 mg/L treatment wasdiscovered,and Hayward was more susceptible to the adverse effect of CPPU than Qinmei.CPPU also reduced the storage ability of fruits,decreased fruit firmness,increased respiration rate and ethylene release rate,and accelerated the process of ripening and senescence.2.Preharvest CPPU treatment accelerated the degradation of protopectin and cellulose,improved the cell wall degrading enzyme activities,such as PME,PG,Cx and?-Gal,increased the accumulation of active oxygen species and content of MDA,decreased the content of antioxidant GSH and the antioxidant enzyme activities,such as POD,CAT and APX in Qinmei kiwifruit.Meanwhie,Preharvest CPPU treatment accelerated the degradation rate of cell wall,mitochondria and starch during storage,damaged the integrity of organelles and membrane system,resulting in the decreased of fruit firmness and the storability of the kiwifruit and shortened the storage life.Preharvest CPPU treatment obviously decreased the cellulose content,improved the activities of PME and?-Gal,reduced the antioxidant enzyme activities,such as POD,CAT and APX,resulting in rapidly degrading of starch granules and intercellular substance on the harvest day,and reducing the fruit firmness in Hayward kiwifruit,those result different from Qinmei.According to the correlation analysis,the main enzymes related to fruit softening of the two cultivars were different,Qinmei were PG and Cx,but Hayward were Cx,?-Gal.3.Preharvest CPPU treatment affected the cell wall degradation and reactive oxygen metabolism of kiwifruit,resulting in different ultrastructural changes of the two varieties kiwifruit.With the increase of CPPU concentration,it promoted the rate of respiration and ethylene release of fruit,accelerated the degradation of protopectin and cellulose,improved the activities of main enzymes related to fruit softening,such as PG and CX,increased the content of O₂^·-and MDA in the cells,meanwhile significantly reduced the content of antioxidant GSH and activities of antioxidant enzymes,such as POD,CAT and APX.All factors above lead the damage degree of cell structure increased,the edible quality reduced,the process of ripening and senescence accelerated,and the storability of Qinmei kiwifruit decreased.For Hayward kiwifruit,the facts that the content of cellulose rapidly decreased on the harvest day,the?-Gal activities of main enzymes related to fruit softening obviously improved,the activities of antioxidant enzymes,such as POD,CAT and APX,significantly reduced,which enable cell structure of the fruit to be severely damaged,fruit firmness to be rapidly decreased,edible quality to be significantly reduced.However,the facts that the content of protopectin and antioxidant GSH in treated fruit with CPPU increased,the Cx activity of main enzymes related to fruit softening and the content of O₂^·-,MDA decreased,which may be the reason for CPPU had no significant effect on storability of Hayward fruit on the middle and late storage.During postharvest storage,CPPU treatment had a greater effect on the quality of Hayward kiwifruit than that of Qinmei,and had a significant effect on the storability of Qinmei kiwifruit than that of Hayward.In conclusion,the use of CPPU treatment is not recommended in kiwifruit production.