外源EBR对烤烟成熟期氮代谢及烟碱代谢的影响

为探明外源2, 4-表油菜素内酯（2, 4-epibrassinolide，EBR）对烤烟成熟期氮代谢及烟碱代谢的影响，以清水为对照，比较了烤烟打顶后叶面喷施和灌根两种EBR施用方式下成熟期叶片光合特性、干物质积累、氮代谢相关酶活性、烟碱代谢相关基因表达量和烤后烟叶化学成分的差异。结果表明，与对照相比，叶面喷施和灌根两种EBR施用方式均可提升成熟期烟株的光合能力，增加烟株各部位的干物质积累量，显著提升中部和上部烤后烟叶总氮和烟碱含量（质量分数），且叶面喷施处理的效果好于灌根处理。两种施用方式上部叶氮素吸收同化关键酶NR和GS活性显著高于对照处理，叶面喷施处理叶片中氮同化相关基因NtGS2、NtGDH1和NtNR的相对表达量显著高于对照和灌根处理。两种EBR施用方式烟株不同部位烟碱合成基因NtQPT、NtPMT和转运基因NtJAT1、NtJAT2和NtNUP1的相对表达量均极显著高于对照，且叶面喷施处理叶片中烟碱合成与转运基因的表达量均极显著高于对照和灌根处理。因此，外源EBR可促进烟株的生长发育、提高氮代谢及烟碱代谢水平，增加中部和上部烤后烟叶烟碱含量，叶面喷施的效果好于灌根。 

Effects of exogenous 2, 4-epibrassinolide on nitrogen metabolism and nicotine metabolism in flue-cured tobacco at mature stage

In order to investigate the effects of exogenous 2, 4-epibrassinolide (EBR) on nitrogen metabolism and nicotine metabolism in flue-cured tobacco at mature stage, the differences of photosynthetic characteristics, dry matter accumulation, activities of nitrogen metabolism related enzymes, relative expression levels of nicotine synthesis related genes at mature stage, and chemical components of flue-cured tobacco were compared between the treatments of applying exogenous EBR by foliar spraying(T1)and root irrigation(T2), with clear water as the control(CK)after topping. The results showed that compared with CK, applying exogenous EBR by foliar spraying and root irrigation could improve the photosynthetic capacity of mature tobacco plants, increase the dry matter accumulation in various parts of tobacco plants, and significantly increase the contents of total nitrogen and nicotine in cured middle and upper tobacco leaves. The effects of foliar spraying were better than that of the root irrigation applying treatment. The activities of the key enzymes of nitrogen absorption and assimilation, NR and GS, in the upper leaves of the two treatments, were significantly higher than those of CK. The relative expression levels of nitrogen assimilation related genes NtGS2, NtGDH1 and NtNR in the leaves of T1 were significantly higher than those of CK and T2. The relative expression levels of nicotine synthesis genes NtQPT and NtPMT, and transport genes NtJAT1, NtJAT2 and NtNUP1 in different parts of tobacco plants under the two EBR application treatments were significantly higher than those of CK, and the expression levels of nicotine synthesis and transport genes in leaves of T1 were significantly higher than those of CK and T2. Therefore, exogenous EBR could promote the growth and development of tobacco plants, improve the levels of nitrogen metabolism and nicotine metabolism and increase the nicotine content in cured middle and upper tobacco leaves, and the effects of foliar spraying treatment was better than those of the root irrigation treatment.