低温下黄瓜叶柄与叶脉NO3-和NH4+转运差异的分子机制

Nitrogen use efficiency of greenhouse cucumber was often reduced by low temperature in winter, which resulted decrease in production. Cucumber roots absorb nitrogen primarily as nitrate and ammonium. The effect of low temperature on nitrogen use efficiency of cucumber mainly via the transport of nitrate and ammonium in xylem. Our previous studies suggested that nitrate and ammonium ion velocity in petiole xylem were restrained significantly under low temperature (8℃), while nitrate and ammonium velocity in midrib were, respectively, mildly suppressed and significantly improved. This phenomenon and its internal mechanism have not been reported so far. To reveal the molecular mechanism of the difference in the nitrate and ammonium transport in petiole and midvein of cucumber under low temperature, we will study the effects of nitrate reductase (NR) on nitrate and ammonium ion velocity, analyse the relationship between nitrate transporters gene expression and nitrate transport in xylem of leaf petiole and midrib of cucumber (Cucumis sativus ‘Xintai Mici’). The candidate key genes that may significantly affect the nitrate transport will be identified, and the function of these genes will be verified by cucumber genetic transformation technology. The project could provide a theoretical basis for regulating the nitrogen use efficiency of cucumber in greenhouse.

设施黄瓜冬季生产中常遭遇低温，导致其氮素利用效率降低，产量下降。低温主要通过影响NO3-和NH4+的木质部运输影响黄瓜氮素利用。前期研究结果表明，低温(8℃)处理使黄瓜幼苗叶柄木质部NO3-和NH4+离子流速显著降低，叶中脉NO3-离子流速降幅较小，NH4+离子流速则大幅提高，对这一现象及其产生的原因尚未见报道。本项目以‘新泰密刺’黄瓜为试材，研究低温下硝酸还原酶(NR)对NO3-转运过程中的还原和离子流速的影响，分析叶柄和叶脉硝态氮转运蛋白(NRT)家族基因表达与NO3-离子流速的关系，筛选出影响NO3-转运的NRT家族候选关键基因，并利用黄瓜遗传转化体系对其进行转基因功能验证，以阐明低温下黄瓜叶柄与叶脉NO3-和NH4+转运差异的分子机制，为调控设施黄瓜氮素利用效率提供理论依据。

设施黄瓜冬季生产中常遭遇低温，导致其氮素利用效率降低，产量下降。低温主要通过影响NO3-和NH4+的木质部运输影响黄瓜氮素利用，但对于低温影响硝态氮和铵态氮吸收和转运的机制尚缺乏系统研究。本项目以‘新泰密刺’黄瓜为试材，研究了低温下硝酸还原酶(NR)对NO3-转运过程中的还原和离子流速的影响，通过分析叶柄和叶脉硝态氮转运蛋白(NRT)家族基因表达与NO3-离子流速的关系，筛选出影响NO3-转运的NRT家族候选关键基因，并利用黄瓜遗传转化体系对其进行转基因功能验证。主要研究结果如下：.(1)与正常温度（26°C）处理相比，低温（8°C）处理导致黄瓜幼苗对硝态氮、铵态氮和总氮的吸收量显著降低，并导致硝态氮和铵态氮在植株根部积累，在地上部的分配比例降低。.(2)NMT检测结果表明，与26°C处理相比，低温处理导致黄瓜幼苗根毛区和维管束中NO3−净离子流速显著降低。与NO3−不同，低温下幼苗根毛区和主根、茎、叶柄维管束内的NH4+离子流速显著降低，而叶中脉、侧脉和龙头维管束内的NH4+离子流速显著升高。.(3)与26℃处理相比，低温处理的黄瓜幼苗茎和叶柄中NR实际活性（NRAact）显著升高，根中NRAact没有显著差异，说明低温下经黄瓜根、茎和叶柄向上运输的硝态氮更多比例被还原为铵态氮。.(4)与26℃处理相比，低温处理的黄瓜幼苗叶柄和叶中脉中硝态氮转运蛋白基因CsNRT1.4a的相对表达量下调，叶中脉中铵态氮转运蛋白基因CsAMT1.2a–1.2c的相对表达量上调。NRT1.4a是低温下影响黄瓜叶柄和叶脉NO3-运输的NRT家族候选关键基因。.综上，低温处理条件下，黄瓜幼苗通过调控NR活性和氮转运蛋白基因表达调控维管束内的无机氮素运输。项目研究结果将为黄瓜越冬生产中通过调控氮肥硝胺比提高黄瓜氮素利用效率提供科学依据。