| Banana is one of the most popular fruits in subtropical countries and one of the four largest fruits in the world.Because of its soft and waxy taste and rich nutritional value,it is deeply loved by people all over the world.Banana also has a wide range of planting areas in China,which is an important fruit crop with high economic value.However,as a typical respiratory climacteric fruit,banana fruit senescence process is accelerated in the late ripening stage,resulting in shorter storage time.Proanthocyanidins(PA)are polymers of flavan-3-ol extracted from plants and are the most abundant polyphenols in our diet.PA has been proved to have strong antioxidant,anti-aging and prevention of cardiovascular diseases.However,there is no application of PA in postharvest fruits.Therefore,in this paper,exogenous PA was used to treat banana in green mature stage to explore the effect of exogenous PA treatment on postharvest banana fruit ripening and senescence and its mechanism.This paper mainly discusses the effects of exogenous PA treatment on ripening and senescence of postharvest banana fruit from the following aspects.Firstly,the effects of exogenous PA on the quality and physiological changes of postharvest banana fruit were studied.The results showed that compared with the control banana fruit,exogenous PA treatment could delay the yellowing of fruit color and the decrease of pulp hardness,indicating that the H value of fruit color change reached the maximum of 16.55 on the fifth day.Exogenous PA treatment could also delay the accumulation of soluble solids and inhibit the respiration rate and ethylene release rate of fruits.The ethylene release rate had the largest difference on the third day.Secondly,the effects of exogenous PA on banana fruit ripening and senescence were discussed from the aspects of cell wall degradation and membrane damage.The results showed that compared with the control,PA treatment could significantly reduce the activities of polygalacturonase(PG),pectinlyase(PL),pectin methylesterase(PME)and cellulase and the expression of related genes,and inhibit the increase of electrical conductivity and malondialdehyde(MDA)content to a certain extent The conductivity was 16.00% and 16.07%respectively.Then,the effects of exogenous PA on ripening and senescence of postharvest banana were discussed from the aspect of active oxygen metabolism.The results showed that,compared with the control,PA treatment could inhibit the production of free radicals(ROS),increase the activities of antioxidant enzymes superoxide dismutase(SOD),catalase(CAT)and peroxidase(POD)and the expression of related genes,and increase the yield of banana fruit 1,1-diphenyl-2-trinitrophenylhydrazine(DPPH)scavenging capacity of banana fruit in the treatment group was 1.2% higher than that in the control group on the third day.Finally,the accumulation mechanism of proanthocyanidins in banana fruits treated with exogenous PA was discussed.Firstly,the effects of PA treatment on the contents of total phenols,flavonoids,PA and the activities of related enzymes in banana fruits were studied.The results showed that compared with the control,PA treatment could inhibit the decrease of the contents of total phenols,flavonoids and PA,and delayed the decrease of the activities of phenylalanine ammonia lyase(PAL),colorless anthocyanin reductase(LAR)and anthocyanin reductase(ANR).In addition,the peel samples of control fruit and PA treated fruit on the first day were selected for transcriptome sequencing and analysis.The results showed that 1086 differentially expressed genes were induced by PA treatment.Twenty one key genes,including genes related to proanthocyanidin biosynthesis and transcriptional regulators,were screened and verified by quantitative real-time PCR.The results showed that PA treatment could up regulate the expression of these genes during banana storage.In conclusion,exogenous PA treatment can improve PA,total phenol and flavonoids content in banana fruit by improving the activity of PA synthesis related enzymes and related genes,thus improving the antioxidant capacity of banana fruit tissue,reducing membrane lipid peroxidation damage and cell wall degradation,and delaying the quality deterioration and mature aging of banana fruit after harvest. |
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