Dry-Bulb Temperature-Modulated Curing’s Impact on the Carbon and Nitrogen Metabolism of Tobacco Leaves in Clean-Energy Bulk Curing Barns

Abstract

The optimized curing environment in bulk curing barns can enhance the carbon and nitrogen metabolism of tobacco leaves. The impact of dry-bulb temperature (DBT) treatments during the yellowing stage of the tobacco curing (CK: constant yellowing DBT at 38 °C; T1: DBT fluctuation range ±1 °C, frequency of 3 hours; T2: DBT fluctuation range ±1.5°C, frequency of 5 hours) on the carbon and nitrogen metabolism of tobacco leaves was evaluated. (1) After the yellowing stage, the T1 treatment led to lower levels of starch, total sugars, and soluble proteins, but a higher accumulation of free amino acids in tobacco leaves. (2) Despite differences in magnitudes during tobacco curing, carbon and nitrogen metabolism-related enzymatic activities showed similar trends among different treatments. (3) Treated by T1 method, the expression levels of genes encoding starch enzymes (AMY, BMY-1, and BMY-3) in tobacco leaves rose sharply, while the expression levels of genes encoding soluble starch synthases (SSS-1) and pyrophosphorylase (AGPase-1 and AGPase-2) were at their lowest among all treatments during the same period. In addition, the expression levels of genes involved in nitrogen transfer (GS1-3) were higher, whereas the expression levels of genes related to nitrogen assimilation (NR and GS2) were lower. Finally, based on the constant yellowing DBT at 38 °C, the DBT treatment with T1 can promote thorough degradation and transformation of starch and protein, together with the effective accumulation of free amino acids in tobacco leaves. In this way, chemical composition of tobacco leaves can be better optimized, which vastly affects tobacco leaf quality and reduces ineffective curing energy consumption.