Physiological Changes During Ripening Of Flue-cured Tobacco Leaves And Regulation By Exogenous Growth Substances

Abstract Flue-cured tobacco is one of the most economically valuable crops in China.It plays an irreplaceable role in the stability of national taxation and economic development.High quality cigarettes need high-quality raw materials,which require accurate timing for harvesting and curing,and proper maturity.In order to improve the quality and yield of tobacco,reasonable collection standard and corresponding quantitative indices should be set up.In this paper,Yunyan 87,a flue-cured tobacco variety,was used as the experimental material to study the physiological changes in the process of flue-cured tobacco maturation and to establish the physiological indices of timely harvest.By studying the regulation effect of exogenous growth substances on the aging process,effective growth regulators were selected to regulate the maturation of tobacco leaves and improve tobacco maturity tolerance.The main results are as follows:1.Development process and physiological changes of tobacco leaves at different stalk positionsThrough field investigation,the number of days in each stage of growth and development was revealed,and the difference in leaf maturity duration was obtained.The lower leaf needed 5 days from maturation to over-maturation and the middle leaf needed 11 days,and the upper leaf needed 13 days.The ripeness of the upper leaf was better than that of the lower leaf and middle leaf.A series of physiological changes have taken place in tobacco leaves during their development and maturation.When leaves fully expanded,the specific leaf weight is still growing,but begins to decline after reaching the maximum value.SPAD value,chlorophyll(Ch1)content,carotinoid(CAR)content and membrane stability index(MSI)decline continuously and showing relatively slow in the early and accelerating in the later.CAR/Ch1 shows a slow rise at first and then a significant increase.The expression level of physiological characteristics of leaves in different parts is various,but the change trend is basically the same.The changes of each index in the upper leaves were obvious.Based on relationship between physiological changes and quality of flued-cured tobacco,physiological indices for leaves at different stalk positions were set up.The lower leaves had reached the highest value after the leaf weight,and fell back to the fixed long-term level.SPAD was down to the fixed long-term 57～41%.CAR/Chi value was about 0.16.The protein content reduced to a fixed long-term 75%or so.MSI reduced to the fixed long-term 77～65%during harvesting and baking is more appropriate.During this period,the leaves were green with yellow,the main vein 1/2～3/4 above was white,the branches was green slightly yellow,and tip prolapse.The middle leaves fell to about 95%after the highest value of leaf weight.SPAD was down to the fixed long-term 84～70%.CAR/Ch1 value was reach the 0.17～0.18.The protein content was reduced to about 74%of the long-term.MSI reduced to the fixed long-term 80～72%during harvesting and baking is more appropriate.The main morphological characteristics of the leaves are yellow with green color,the main veins are shiny or white light,1/3～2/3 above the branches of white to pale and bright,mature spots appear.The upper leaves fell to about 87%in the fixed long-term after the weight of the specific leaf weight;SPAD was dropped to the fixed long-term 35%;and the value of CAR/Chl reached 0.209～0.204;the protein content decreased to about 72%in the fixed long-term;and MSI reduced to the fixed long-term 55.7%during harvesting and baking is more appropriate..Leaf shape features yellow green leaf color,yellow in main vein,yellow in branch vein,white and white in main branch,white petiole,part of focal point,no scorch edge,and matured spot.2.Physiological and biochemical regulation effects of exogenous substances on the maturation process of flue-cured tobacco leaves.(1)Effects on endogenous hormones.Exogenous SPN,BR and Spd can increase the content of IAA and t-ZT,and reduce ABA and JA content;but the exogenous MeJa has the opposite effect.Compared with SPN,BR and Spd treatment,the effects of SPN and BR on IAA and t-ZT are obvious,but there is no significant difference in the regulation effects of ABA and JA content between three.(2)Effects on Chlorophyllase activity.With the development of leaf development,the activity of Chlase increased slowly,then increased rapidly,and then decreased.Using exogenous bioactive material treatment,the change trend of Chlase activity was relatively small,but it had a great influence on the enzyme activity level at different stages.The Chlase activity of SPN,BR and Spd was lower than that of the control group,while the treatment of MeJa significantly improved the Chlase activity of the leaves.(3)Effects on chloroplast pigment contents.SPN,BR and Spd treatment had the effect of inhibiting the activity of Chlase,and MeJa significantly improved the Chlase activity of the leaves.Therefore,SPAD value and Chl content of SPN,BR and Spd were higher than that in the control group,while the SPAD value and Chl content of MeJa treatment were significantly lower than that in the control group.(4)Influence on cell membrane stability index.The membrane stability index(MSI)was slowly reduced within 15 days after treatment,and the MSI decrease was accelerated after 20 days,SPN,BR and Spd treatment were all slightly higher than those in the control group,indicating that these three treatments could enhance the film stability of the leaves,while the MeJa treatment resulted in significantly lower MSI than the control.(5)Effects on the yield and quality of flue-cured tobaccoDays for high quality holding of SPN,BR and Spd treatment were 13 days,12 days and 11 days respectively,while MeJa treatment lasted only 7 days.Compared with the control group,the treatment of SPN,BR and Spd significantly improved theholding ability of tobacco leaves,while MeJa had the effect of accelerating the aging of tobacco leaves and reducing the number of days for high quality holding.At the same time,the treatment of exogenous active substances also affected the yield and quality of flue-cured tobacco.SPN,BR,and Spd treatments significantly increased yield and quality,while the yield and quality of flue-cured tobacco treated with MeJa were lower than those of the control group.