Spermidine Regulating Endogenous Polyamines And Ethylene Synthesis In Saimaiti Apricots Postharvest

Saimaiti apricots are one of the main varieties with excellent quality,unique taste in Xinjiang.Apricot is a climacteric fruit,ethylene?C₂H₄?plays a very important role on the climacteric fruit ripening and softening.Previous studies have shown that exogenous spermidine?Spd?effectively delay the ripening and senescence of apricot fruits.In order to study the effect of Spd on endogenous polyamines?PAs?and C₂H₄ synthesis in apricot,used the green stage of Xinjiang Saimaiti apricots as the meterials,treated with Spd,C₂H₄ and D-Arg,studied quality changes,endogenous PAs?Put,Spd and Spm?contents,respiration,C₂H₄ and its related gene expression during storage.To clarify the interaction between Spd and C₂H₄,reveal the mechanism of the interaction between Spd and C₂H₄,and provide new ideas and theoretical references for the research and application of Spd in agricultural products.The main results are as follows:?1?The green stage Saimaiti apricots at postharvest treated with Spd could effectively maintain fruits firmness,delay the decomposition rate of titratable acid and chlorophyll,reduce fruit decay degree;Spd+C₂H₄ treatment increased AsA contents of apricot fruits;D-Arg and ethephon treatments have similar results.They can accelerate softening speed;promote the ripening and senescence of Saimaiti apricots.?2?The appreproiate conditions on the extracting and deriving of the polyamines was obtained.The solid-liquid ratio 1:2,the extration time 2 h,benzoyl chloride dosage 15?L,30?react 20 min.The separation condition was Eclipse Plus C18 column with methanol:acetonitrile:water?60.5:2.5:37,v/v/v?as the mobile phase at a flow rate of 0.8 mL/min.Put,Spd and Spm retention time were 6.8 min,10.8 min and 17.8 min.Through high performance liquid chromatography method determined of polyamines content at defferent stage of apricot fruits,we found that Spm>Spd>Put content.Compared with CK,C₂H₄ and D-Arg treatments could influence the synthesis of endogenous polyamines in apricot fruits,decreased the contents of endogenous Put,Spd and Spm,thereby promoting the fruit senescence.?3?Spd treatment could reduce the respiration rate and delayed respiration peak of apricot fruits.At the same time,it could inhibit the activity of ACC synthase and ACC oxidase,respectively.Reduce the content of ACC content directly,inhibited ethylene production,thereby delaying fruit ripening and senescence.D-Arg could enhanced the activity of ACC synthase and ACC oxidase and promote ethylene production.?4?The expression levels of PaACS1,PaACS2,PaACS3 and PaACO were different in the postharvest Saimaiti fruit.Among them,changes of PaACS1 and PaACS3 expression levels were not obvious in Spd and D-Arg treatments.Through inhibited of PaACS2 and PaACO mRNA transcript levels,Spd influenced its expression and regulated of ethylene synthesis.However,D-Arg had an up regulation on PaACS2 and PaACO.Low temperature also inhibited the expression of PaACS2 and PaACO,but the expression of PaACS1 and PaACS3 were not affected by temperature.PaACS2 played a major role in ethylene biosynthesis.