烤烟不同成熟度上部叶中抗性淀粉与淀粉组分的变化及其与基因表达的关系

Changes of resistant starch contents and starch components in upper leaves of flue-cured tobacco at different maturity stages and their relationship with gene expression

【目的】为研究烤烟上部叶在成熟后期及烘烤过程中淀粉组分和抗性淀粉含量的变化。【方法】以烤烟品种云烟87上部叶为试验材料,分析不同成熟度鲜烟叶及其在烘烤过程中淀粉组分和抗性淀粉含量的变化,阐明抗性淀粉和淀粉组分的相关性,通过实时定量PCR探究不同成熟度烟叶中淀粉合成相关基因的表达模式。【结果】(1)随烟叶不断成熟,淀粉粒数量迅速变多、体积增大,烟叶变黄时,叶绿体开始解体,淀粉粒逐渐降解。(2)不同成熟度鲜烟叶中直链淀粉含量与支链淀粉含量:欠熟>适熟>过熟,而抗性淀粉含量差异不大;在烟叶衰老过程中,支链淀粉迅速降解,而直链淀粉和抗性淀粉缓慢降解。(3)在烘烤过程中,淀粉降解主要集中在变黄期。烘烤结束后,烤烟中未降解的淀粉约50%为抗性淀粉。(4)淀粉合成基因葡萄糖-1-磷酸腺苷酰转移酶小亚基3(AGPS3)、葡萄糖-1-磷酸腺苷酰转移酶大亚基(AGPL)、颗粒结合型淀粉合酶(GBSS)、可溶性淀粉合酶2(SS2)、1,4-a-葡聚糖分支酶(SBE1)、2,3淀粉分支酶2(SBE2)和异淀粉酶2(ISA2)在欠熟烟叶中的基因表达水平较高,随烟叶衰老表达水平下调,而异淀粉酶3(ISA3)的基因表达水平在烟叶衰老过程中持续上调。【结论】烤烟不同成熟度上部叶中存在抗性淀粉,烘烤过程的变黄期是烟叶内淀粉降解的主要时期,但大田期形成的抗性淀粉很难在烘烤过程中充分降解。因此,可以通过适当推迟烟叶采收,降低烤烟淀粉含量,从而提高上部叶可用性。

[Background]This paper aims to study the changes of starch components and resistant starch content in upper leaves of flue-cured tobacco at different maturity,in order to provide reference for improving the maturity,reducing the starch content and improving the availability of upper leaves in flue-cured tobacco.[Methods]By taking the upper leaves of Yunyan 87 as research material,the changes of starch components and resistant starch contents in tobacco leaves at different maturity as well as the correlation between resistant starch and starch components were analyzed.The expression patterns of starch biosynthesis related genes were analyzed by real-time quantitative PCR.[Results](1)Microscopic analysis revealed that the number and volume of starch granules increased gradually and reached maximum values at the mature stage.When tobacco leaves turned yellow,chloroplasts began to disintegrate and starch grains gradually degraded.(2)Starch content analysis showed that the resistant starch existed in mature tobacco leaves.The contents of resistant starch,amylose and amylopectin in leaves at different maturity stages were significantly different,which were the highest in un-riping leaves,followed by well-ripening leaves,and least in over-ripening leaves.During the aging process of tobacco leaves,amylopectin was rapidly degraded,while amylose and resistant starch were slowly degraded.(3)During the curing process,starch degradation mainly occurred in the yellowing stage.After flue-curing,about 50%of un-degraded starch in tobacco was resistant starch.(4)The gene expression levels of glucose-1-phosphate adenylyltransferase small subunit(AGPS3),glucose-1-phosphate adenylyltransferase large subunit(AGPL),granule-bound starch synthase(GBSS),probable starch synthase(SS2),1,4-alpha-glucan-branching enzyme-like(SBE1),2-3 starch branching enzyme 2(SBE2)and isoamylase 2(ISA2)were higher in immature tobacco leaves,and decreased gradually with the aging of tobacco leaves,while the gene expression level of isoamylase 3(ISA3)increased continuously during the aging process.[Conclusion]Resistant starch exists in the upper leaves of flue-cured tobacco.Starch in leaves can be degradated mainly at the yellowing stage,whereas resistant starch formed during leaf development is difficult to be degraded fully during roasting.It may be an effective way to reduce the starch content of flue-cured tobacco and improve the availability of upper leaves through preventing the amylase synthesis in tobacco leaves.