Changes In Physiological Metabolism During Natural Ageing In Middle Leaves Of Tobacco Varieties With Differential Leaf Senescence

The mature senescence characteristics of tobacco leaves are closely related to the quality of tobacco leaves.In order to regulate the aging process of tobacco leaves and provide reference for breeding varieties with suitable aging characteristics,Yuyan 10,Yunyan87,K326 and NC89 with different mature yellowing characteristics were selected as materials and were planted under the same conditions in the field,the changes of maturation and senescence characteristics,carbon and nitrogen metabolism,endogenous hormone and related gene expression in the middle leaves of four varieties at different leaf ages were studied.The main findings are as follows.There were significant differences in the degradation of pigments and the process of leaves yellowing senescence between tobacco varieties,by comparing the maturity and senescence characteristics of middle leaves of four varieties at different leaf ages.Leaves of Yuyan 10 had earlier yellowing time,higher degradation of plastid pigment and higher expression of carotenoid degradation gene(CCD)compared with that of NC89.The expression of senescence-associated genes(NtCP1,NtCP23)in the middle leaves of Yuyan 10 was higher and with a large range of changes.The expression of senescence-down regulated genes(PSA1,MC)gradually decreases with leaf maturity and the ripening process,and the expression of Yuyan 10 leaves decreases significantly compared with NC89 leaves.It indicated that the expression of senescence marker gene was consistent with the process of leaf maturity and ripening.Through the black box treatment of the leaves of four varieties with leaf age of 60 days,it found that the yellowing speed of Yuyan 10 and Yunyan 87 was the fastest;the browning speed of Yuyan 10 was the fastest,and Yunyan 87 and K326 were the slowest,which indicated that the mature senescence characteristics of different flue-cured tobacco varieties were genetically different.By measuring and analysis the carbon and nitrogen metabolism related indicators and gene expression in the process of the maturity and senescence characteristics of middle leaves,this paper found that NC89 starch content peak appeared relatively late.Compared with Yuyan 10,NC89 had higher starch content and less degradation.The expression levels of related genes(GBSS1,SBE)involved in starch synthesis were consistent with the changes in starch content.The soluble sugar content of Yuyan 10 reached a peak at 50 days of leaf age which was significantly lower than NC89 after this period.Compared with NC89,the total nitrogen content of Yuyan 10 was significantly lower than that of NC89 at 70 days of leaf age,and the increase of C/N was large.The expression of GS1-3 gene related to nitrogen transfer was significantly higher than that of NC89 after 40 days of leaf age.The expression of GS2 associated with nitrogen assimilation was significantly lower than that of NC89.Compared with NC89,Yuyan 10 with faster mature yellowing had the characteristics of weak carbon metabolism and weaker ability to metabolize nitrogen in the mature senescence process.The senescence characteristics of tobacco leaves were closely related to their own hormone metabolism.By measuring the related hormones and gene expression during the maturity and senescence process of middle leaves of four varieties at different leaf ages,the research found that:Compared with NC89,Yuyan 10 decreased significantly in the anti-aging function of hormones(IAA,GA3,CTK)at 50 days of leaf age,and abscisic acid(ABA)which promotes senescence was significantly higher than NC89 after 60 days of leaf age.The expression of ethylene regulatory gene NtEFE26,ABA regulatory gene NtNCED1 and jasmonic acid response gene NtPR1b in Yuyan 10 was higher than that in NC89,while salicylic acid response gene expression NtCHN50 of Yuyan 10 was lower.Therefore,the varieties with mature yellowing characteristics had strong metabolism of ABA,ethylene and jasmonic acid.The mature senescence characteristics of different flue-cured tobacco varieties are genetically different.In the process of maturity and senescence of tobacco leaves,the characteristics of varieties with fast aging rate are:large amount of starch degradation,early peak of reducing sugar content,strong ability of nitrogen assimilation to weak nitrogen transfer;weak IAA,GA3,CTK metabolism,ABA,ethylene,strong jasmonic acid metabolism.