不同采烤方式对烤烟上部叶脂质褐变的影响
Effects of different harvesting and baking methods on lipid browning of upper leaves of flue-cured tobacco
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摘要: 【目的】明确烤烟上部叶不同采烤方式对烟叶褐变的影响，探索适宜的采烤方式，为提高上部叶可用性提供理论指导。【方法】以正常采烤处理烟叶（CK）、2片叶带茎烘烤（T1）、4片叶带茎烘烤（T2）和6片叶带茎烘烤（T3）的上部叶为试验材料，利用透射电镜、扫描电镜和基因表达量分析技术从细胞结构和基因分子水平层面，探讨采烤方式对上部烟叶脂质褐变的影响，并分析烟叶脂肪酸含量、角质层厚度和脂氧合酶（LOX）活性之间的相关性。【结果】不同处理烘烤中烟叶褐变速度排序为： 6片叶带茎烘烤处理<4片叶带茎烘烤处理<2片叶带茎烘烤处理<正常采烤处理，其中4片和6片叶带茎烘烤处理烟叶烤后褐变比例较CK分别减少1.34%和4.22%（绝对值），褐变反应受到抑制。超微结构观察结果显示，带茎处理烟叶烘烤过程中角质层厚度随叶片数量增加而分别减少34.09%、43.86%和46.40%。与CK相比，6片叶带茎烘烤处理下脂肪酸总量、油酸和亚麻酸含量极显著降低（P<0.01，下同），棕榈酸、亚油酸含量及LOX活性显著降低（P<0.05）。检测脂肪酸代谢相关基因的表达量发现，带茎烘烤处理中LOX5、LTP4、MYB48、MYB108、CER3和ALDH2B7的表达均明显受到抑制，其中6片叶带茎烘烤处理的脂质氧化关键基因LOX5相对表达量下调56.03%。相关分析结果表明，角质层厚度与硬脂酸和脂肪酸总量呈极显著正相关、LOX活性与油酸和亚麻酸含量呈极显著正相关。【结论】脂肪酸代谢是影响烟叶褐变的重要原因之一。6片烟叶带茎采烤处理在烘烤高温高湿环境中能通过降低烟叶LOX脂质氧化活性、减少烟叶脂肪酸积累及抑制相关脂质基因的表达来调控减缓烟叶褐变速度。Abstract: 【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 stems
P<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.
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