| The upper leaves,which account for 30% to 45% of the entire tobacco plant,play a dominant role in the cigarette leaf group formulation because of their thick and full aroma concentration,which is conducive to increasing the eating flavor concentration.As the upper leaves are well-lit,the identity of the cured tobacco leaves is thick,and the content of starch and other macromolecular organic matter is high,which makes it easy to cure green and hang ash during the curing process,resulting in low industrial availability of the upper leaves of tobacco.To explore the content of starch fraction during the growth and development of tobacco leaves and curing process,and to screen the starch synthesis-related genes associated with resistant starch by analyzing the accumulation characteristics of resistant starch,which can provide a reference for reducing the starch content of tobacco leaves after curing and improving the availability of upper leaves.In order to clarify the changes of starch content during the growth and development of tobacco leaves and the curing process,this study analyzed the effects of different varieties(lines),different maturity levels and different drying processes on the content of amylose and amylopectin,and measured the resistant starch content of tobacco leaves during the test,and also studied the accumulation characteristics of resistant starch and the relationship between the expression of genes related to starch synthesis during the growth and development of tobacco leaves.The main findings are as follows:1.The content of amylose,amylopectin and resistant starch varied among varieties of tobacco as the number of days of transplanting increased.The amylose and amylopectin content of K326 and Yunnan 87 tobacco leaves showed an increasing and then decreasing trend,while the amylose and amylopectin content of CB-1 tobacco leaves showed a continuous increasing trend.The expression of GBSS genes was significantly up-regulated from 70 to 80 d after transplanting,and the expression of AGPS1,AGPS2,AGPS3 and AGPSL genes in K326 and Yunnan 87 tobacco leaves was higher in the first and middle stages of tobacco development(50-70 d after transplanting),while the expression of genes regulating amylose synthesis in CB-1 tobacco leaves was higher in the middle and late stages of tobacco development(60-90 d after transplanting);The SS,SBE and ISA activities played an important role in the accumulation of amylopectin in tobacco leaves.The SS1,SBE2 and ISA3 genes in Yunnan 87 and CB-1 tobacco leaves had high expression throughout the growth and development of tobacco leaves,while the SS1,SS2,SBE2 and ISA2 genes in K326 tobacco leaves had lower expression during the development of tobacco leaves.Differences in the expression of GBSS,SS and SBE genes may be responsible for the different contents of amylose and amylopectin in different varieties of tobacco,which further affects the content of resistant starch in tobacco leaves.2.As the maturity of CB-1 tobacco leaves increased,the amylose,amylopectin and resistant starch contents of tobacco leaves showed a continuous decreasing trend.The amylose content of unripe,moderately ripe and overripe tobacco leaves were 12.60%,11.80% and 10.20%,respectively,while the amylopectin content of unripe,moderately ripe and overripe tobacco leaves were 25.40%,19.70% and 14.30%,respectively,with the overall starch content showing unripe > moderately ripe > overripe.The gene expression levels of the amylose synthesis-related gene GBSS and the amylopectin synthesis-related genes SS2,SBE1 and SBE2 were higher in unripe tobacco and were down-regulated with tobacco senescence,while the gene expression level of ISA3 was consistently up-regulated during tobacco senescence.Harvesting at the right maturity is an effective measure to reduce the starch fraction and resistant starch content of the upper leaves of CB-1 and to improve the availability of the upper leaves of CB-1.3.As the curing process continued,the contents of amylose,amylopectin and resistant starch in CB-1 tobacco gradually decreased.In the middle of the pre-yellowing period(0~48h),amylose,amylopectin and resistant starch contents were all degraded substantially,and the degradation of amylose was 58.03%,22.92%,48.81% and 51.40% for local conventional curing process CK,low temperature yellowing curing process T1,medium temperature yellowing curing process T2 and high temperature yellowing curing process T3,respectively,and the degradation of amylopectin was 58.74%,34.23%,50.13% and 53.56%,respectively.were 58.74%,34.23%,50.13%,53.56%.The main yellowing temperature affected the resistant starch content,and the total degradation of resistant starch was 64.27%,54.01%,73.34% and 63.34% in the local conventional curing process CK,low temperature yellowing curing process T1,medium temperature yellowing curing process T2 and high temperature yellowing curing process T3 treatments,respectively.Among them,when the main yellowing temperature was 38 ℃,extending the main yellowing time could effectively reduce the resistant starch content in the post-curing tobacco leaves.The comprehensive analysis concluded that for the upper leaves of CB-1 tobacco,the medium-temperature yellowing curing process was used to extend the main yellowing time,which could reduce the resistant starch content of post-curing tobacco,and then provide a reference for reducing the starch content of tobacco and improving the quality of tobacco. |
