Effect Of Melatonin On Postharvest Fruit Quality And Mechanism Of Delaying Kiwiberry Fruit Cold Damage

Kiwiberry fruit is a typical respiratory jump variable fruit,which is easy to occur in low temperature storage after harvest,which seriously affects its storage quality and commodity value.Previous studies have reported that melatonin treatment can enhance fruit cold tolerance.Therefore,in this paper,"lvmi-1"kiwiberry as a test fruit,it is a new variety of kiwiberry fruit bred by Yinnoshi Agricultural Science and Technology Co.,Ltd.,Longquan village,Zhongli town,Yucheng district,Ya’an City,Sichuan Province.Using concentrations of 0,50,100,200 and 500μmol·L^-1melatonin solution by immersion for 20min,in order to screen out the melatonin concentration that can prolong the storage time and improve the best kiwiberry fruit quality,to explore the effect of melatonin on kiwiberry fruit quality and cold damage.The analysis of melatonin treatment was mainly from the perspective of refrigeration quality,reactive oxygen species metabolism and proline anabolism,to explore the molecular mechanism of melatonin treatment combined with cold damage-related gene expression.The main study results are presented as follows:（1）Melatonin treatment at different concentrations(50,100,200 and 500μmol·L^-1)can effectively delay the decline of kiwiberry fruit firmness and reduce the weight loss rate and decay rate of kiwi fruit.The concentration of 100μmol·L^-1MT significantly delayed the decrease of kiwiberry fruit firmness,and reduced the weight loss rate and decay rate of kiwiberry fruit during storage.Therefore,the subsequent experiments were compared with100μmol·L^-1MT treatment and control.（2）100μmol·L^-1MT delayed the decrease of firmness and weight loss rate of kiwiberry fruit during cold storage,delayed the degradation of chlorophyll and carotenoids,increased the soluble solid content,promoted the decomposition of titrated acid,enhanced the fruit with SPS and AL enzyme activity and gene expression levels,inhibition of the AI,SS and the NI enzyme activity and gene expression levels,thus improved the accumulation of fructose,glucose and sucrose content in kiwiberry fruit during cold storage,delard the decrease in starch content,delayed the decrease of APX and DHAR enzyme activity,increased GR and MDHAR enzyme activity,upregulated ascorbic acid pathway genes expression levels,so as to maintain postharvest fruit quality,delay the fruit senescence.（3）100μmol·L^-1MT reduced the cold damage index and browning index of kiwi fruit, improve the enzyme activity of SOD,POD and CAT and gene expression levels,delay the rise of MDA content,effectively inhibit the production rate of O₂.^-,delayed the PAL and CHI with decreased enzyme activity,increated the benzylpropane metabolism pathway genes expression levels,increased the Aa P5CS and Aa OAT gene transcript levels,and decreased the Aa PDH gene transcription levels,increased the transcription levels of Aa ICE1,Aa CBF1 and Aa CBF3 cold damage response genes,triggering proline accumulation,enhancing fruit antioxidant capacity and thus increased fruit cold tolerance,reduce the occurrence of fruit cold damage.