Effects of different harvesting and baking methods on lipid browning of upper leaves of flue-cured tobacco

【Objective】To clarify effects of different harvesting methods on tobacco browning in the upper leaves of flue-cured tobacco，to explore the appropriate harvesting methods，so as to provide theoretical guidance for improving the availability of upper leaves.【Method】The upper leaves of the normal harvesting treatment（CK），2 flue-cured leaves with stems（T1），4 flue-cured leaves with stems（T2）and 6 flue-cured leaves with stems（T3）were used as test materials.Effects of harvesting methods on lipid browning of upper leaves at the cell structural and gene molecular levels were explored using transmission electron microscopy，scanning electron microscopy and gene expression analysis techniques.And correlation between fatty acid content，cuticle thickness and lipoxygenase（LOX）activity of tobacco leaves was also analyzed.【Result】The order of browning rate of tobacco leaves in different treatments was： 6 flue-cured leaves with stems<4 flue-cured leaves with stems<2 flue-cured leaves with stemsP<0.01，the same below），and palmitic acid，linoleic acid，and LOX activities decreased significantly（P<0.05） in the treatments of flue-curing with stems compared with CK.Through detecting expression of fatty acid metabolism-related genes，expression of LOX5，LTP4，MYB48，MYB108，CER3 and ALDH2B7 were suppressed in the treatments of fluecuring with stems，among which relative expression of LOX5，a key gene for lipid oxidation，was down-regulated by 56.03%.Correlation analysis showed that cuticle thickness had an extremely significant positive correlation with stearic acid and total fatty acid content while LOX activity had an extremely significant positive correlation with oleic acid and linolenic acid.【Conclusion】Fatty acid metabolism is one of the important causes of tobacco browning.Six flue-cured leaves with stems treatment in high-temperature and high-humidity environment can regulate and slow down tobacco browning rate by reducing LOX lipid oxidation activity，decreasing fatty acid accumulation in tobacco and inhibiting the expression of related lipid genes.