Study On The Effect Of Caspase-like Gene On The Pulp Breakdown Of Postharvest Longan Fruit

Longan is one of the most important fruit in south China.However,longan matures at high temperature in summer,and postharvest physiological metabolism is vigorous.The phenomenon of rapid softening,dissolving and putrefying occurs within 3-4 days after harvest,which is called "pulp breakdown",and seriously affects postharvest storage and sales.Previous studies have suggested that longan pulp breakdown may be a kind of programmed cell death（PCD）in plants,and caspase-like related gene and enzyme play key role in PCD process.Studies have shown that abscisic acid and gibberellin play an antagonistic role in regulating plant PCD.In this study,the breakdown characteristics and changes in enzyme activity like caspase-3 and VPE of longan cv.’shixia’ and ’dongbi’ were compared at normal temperature and low temperature storage.Combined with family analysis and relative expression of caspase-like gene,the effect of caspase-like gene on longan pulp breakdown was analyzed.Using longan cv.’shixia’ as experimental material,with different concentrations of abscisic acid and gibberellin,the physiological indexes,enzyme activity and gene expression were observed and measured to explore the mechanism of plant hormones on longan pulp breakdown.The experimental results are as follows:1.During storage,the browning index of the inner and outer longan pericarp,pulp breakdown index,mildew rate and weight loss rate of longan fruit showed an increasing trend,while the contents of total soluble solids decreased,and the color of outer pericarp deepened and darkened.Under normal temperature storage,the ’shixia’ longan and’dongbi’ longan appeared autolysis from 4d,with poor storage resistance.Under low temperature storage,longan of ’dongbi’ appeared autolysis on 21d,while longan of’shixia’ appeared autolysis on 35d.Longan of ’shixia’ showed good storage performance and lost its storage value on 49d,while longan of ’dongbi’ showed poor storage performance and only reached 42d.The activity of caspase-like increased with the storage time,both of which were significantly correlated with the autolysis index.2.7 metacaspase family members,4 legumain family members and 120 subtilase family members were screened out from longan genome.Based on the prediction of gene structure and location,the caspase-like family is widely involved in a variety of metabolic regulation in cells.According to the evolutionary tree analysis with other plants,it was found that the caspase-like family was similar to other plants in functional structure,and directly or indirectly involved in plant PCD regulation.The expression level of metacaspase in longan flesh was relatively high,and most of the caspase-like genes in ’shixia’ flesh were down-regulated during normal temperature storage,while the expression level of the caspase-like genes in ’dongbi’ longan was not significantly changed,while the expression level of the caspase-like genes in longan longan was different under normal temperature and low temperature storage.Dlo₀33586.1,Dlo₀29089.1,and Dlo₀19047.1 were expressed in longan pulp changed significantly,which has research value.3.Compared with the control group,the treatment of 500 mg/L sportak+100 mg/L abscisic acid can delay the pulp autolysis,but the commodity rate is low.At room temperature,the solution of 500 mg/L sportak+50 mg/L gibberellin can effectively delay longan autolysis and maintain a high commodity rate.The preservation mechanism of longan with low concentration gibberellin can be further explored.4.The activity of caspase-3 and VPE enzymes treated with 500 mg/L sportak+100 mg/L abscisic acid was lower than that of other treatments,and the expression of caspase-like gene in pulp was also lower than that of other treatments.ABA may have a certain regulatory effect on the delay of PCD in pulp.Caspase-3,VPE enzyme activity and caspase-like gene expression in pulp were all higher than that in 500 mg/L+50 mg/L gibberellin treatment,GA and ABA had antagonistic effect.