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Plum(Prunus salicina L.)is the fruit of Rosaceae family,which grows mature during July and August.The plum fruit is sensitive to chilling injury during low temperature storage.Gibberellic acid(GA)is a phytohormone.The GA3 showed effectively to keep fruit quality,to delay the generation of reactive oxygen species(ROS),and to preserve the completeness of the cell membrane.The chemical also decrease the ethylene release of fruit.In this study,plums(cv.Ruby)were pre-harvest sprayed with GA3 at 100ppm at three periods(a week before fruit expanding stage,fruit expanding stage,a week after fruit expanding stage)single or combination.After harvest the treated fruit were packed with PE film(0.04mm)and intermittent warming(IW)every 14days during storage at 0℃,to research effect of pre-harvest GA3 treatment on chilling injury and partial mechanism.The results indicated as below:The treatments significantly decreased chilling injury index and pulp browning index of plums,Compared with the control,the optimum treatment for GA3 was sprayed for 3 times at a week before fruit expanding stage,fruit expanding stage and a week after fruit expanding stage.The treatments decreased the content of H2O2 and O2-and maintain membrane permeability,reduced the MDA content,increased the activity of SOD and CAT,decreased the activity of POD and PPO.The treatments decreased the activity of PAL and 4CL,reduced content of total phenols,flavonoid and lignin.Phenolic compounds were determined lower in treated fruit by HPLC.The treatments maintained the firmness and soluble solids content,delayed content decrease of titratable acidity and ascorbic acid.It is suggested that preharvest GA3 sprays combined with postharvest MAP and IW significantly reduced CI of plum by inhibiting phenylpropanoid pathway,enhance the activity of anti-oxidation enzymes during low temperature storage.