| Apricot occupies a place in the characteristic forest and fruit industry in Xinjiang,and is the main economic source of fruit farmers.Xinjiang apricot market time is short and concentrated,and it is far away from the main consumer market in the mainland.During the transportation,it often leads to loss and waste,and the softening of ripening fruit has become the key issue restricting the transportation of apricot fruit.It is of great significance to study the changes of ethylene biosynthesis,signal transduction and pectinase in the process of apricot fruit development and ripening from molecular and physiological aspects,so as to solve the problem of loss and waste caused by ethylene induced fruit texture changes in the process of apricot fruit development and ripening.In our study,‘Luntaibaixing’,‘Kuchebaixing’ and ‘Kumaiti’ 3cultivars apricots were used as research materials,there were significant differences in fruit firmness and storage time among the three apricot cultivars,and the ripening time was basically the same,the basic growth,the quality change,the ethylene synthesis and the metabolism process and the pectin metabolism enzyme during fruit development were studied;the process of ethylene synthesis and the metabolism during the stage of fruit color changing to ripening;the physiological changes and ethylene metabolism changes of fruits treated with 1-MCP and ethylene after harvest;the transcriptome sequencing of 3 stages in apricots.The changes of ethylene metabolism and synthesis in the fruits at different stages and postharvest were studied,the relationship between ethylene and fruit quality and pectin metabolizing enzymes,the key genes of ethylene metabolism signal transduction and pectinase metabolism provide theoretical support for the physiological and molecular research of ethylene regulation on apricot fruit ripening.The main results are as follows:(1)The dynamic curve of fruit development of the 3 cultivars was ‘double S’ curve,that is,the growth law of fast,slow and fast.Combined with phenological stage,the fruit development process was divided into five stages,namely the young fruit stage(14-21 d after flowering),the expanding stage(21-35 d after flowering),the stone hardening stage(35-49 d after flowering),the color-changing stage(49-63 d after flowering)and the ripening stage(63-77 d after flowering).The fruit quality of the 3 cultivars changed greatly in the latter color-changing stage and ripening stage.The fruit firmness of ’Luntaibaixing’ apricot was significantly lower than that of the other two cultivars(P < 0.05),and ’Luntaibaixing’ apricot was the most intolerant to storage among the 3 cultivars.This was related to the physiological and biochemical changes and endogenous hormone content of ’Luntaibaixing’ apricot.(2)During the whole growth and development process,the change trend of ethylene synthesis precursor in flesh tissue was divided into two stages,and basically showed an increasing trend,and the increasing range was significantly different among the 3 cultivars.At different developmental stages,the changes of ACS and ACO activities in flesh tissues of 3 cultivars were consistent with the increasing ethylene release.Ethylene can regulate the ripening of apricot fruit directly or indirectly,and further regulate the activity of pectinase in the cell wall of apricot fruit,so as to promote the fruit firmness of three varieties to decrease significantly.At the same time,ethylene promoted the increase of soluble solid content and climacteric.(3)The ACS activity,ACO activity and ACC content determined the ethylene biosynthesis and the ethylene release of ’Luntaibaixing’ apricot from the color-changing stage to the ripening stage.The ethylene biosynthesis of ’kuchebaixing’ apricot was regulated by the ACS activity and ACC content,the ethylene synthesis in ’Kumaiti’ apricot was mainly affected by the activities of the ACS activity and ACO activity.(4)The exogenous ethylene treatment accelerated ethylene synthesis and respiration during fruit storage,and exogenous ethylene could effectively improve fruit quality.The 1-MCP treatment could inhibit ethylene metabolism in postharvest fruits,thus delaying the ripening process of apricot during storage.Therefore,the exogenous ethylene treatment can improve the quality and taste of apricot fruit during postharvest storage at room temperature,and the 1-MCP treatment can inhibit the ripening,softening and decay of apricot fruit,thus prolonging the shelf life of apricot and increasing the commodity rate.The1-MCP treatment significantly inhibited the increasing rate of ethylene metabolizing enzyme activities and the accumulation of direct precursors to reduce and delay ethylene synthesis.(5)A total of 231.77 GB of clean data was obtained by transcriptome sequencing,and the clean data of each sample was more than 6.34 GB,and the percentage of q30 base was more than 93.49%.The clean reads of the samples in this study were compared with the reference genome,and the compared rate was between 87.22% and 94.19%.Three key genes in ethylene synthesis were identified.The key genes in the ethylene and the ethylene signal transduction are as follows: Pa ACO(PARG13808)、Pa ACS(PARG18370、PARG27229)genes determine the amount of ethylene synthesis.After ethylene synthesis,they transmit and receive signals through key signal transduction genes: Pa ERF(PARG03138)、Pa ETR(PARG03630)and Pa EIL1(PARG17170)thus promoting fruit ripening.Seven key genes of cell wall pectinase metabolism with different expression in different growth stages of three varieties were found,they were Pa PG(PARG10145,PARG20309)、Pa PME(PARG19839,PARG27582)and Pa PL(PARG12928,PARG18623,PARG16026).The FPKM values of 9 key genes related to ethylene metabolism,ethylene signal transduction and cell wall metabolism were screened from the transcriptome of 3 cultivars at 3 stages by q PCR.. |
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