花后干旱对不同施氮水平下小麦GS同工酶基因表达及产量形成的影响

Drought is one of the main environmental factors limiting wheat yield worldwide, and maintenance of green leaf area and net photosynthesis is therefore essential to grain ?lling and yield under drought, which is linearly related to leaf N content. Studies showed that increasing leaf nitrogen content could enhance plant drought resistance, our experiments also confirmed that the ammonia assimilation ability is closely related with drought resistance of wheat seedlings, and deducing increasing nitrogen supply and assimilation efficiency can enhance wheat drought resistance after anthesis, whereas the prediction has rarely been evidenced experimentally. Glutamine synthetase (GS) is the key enzyme involved in nitrogen assimilation, different GS isoenzymes cytosolic GS (GS1) and plastid GS (GS2) exhibited different and unoverlapping roles in different physiological conditions. Wheat GS1 and GS2 genes have been cloned, but their functions and expression regulation have still not well understood. In the present project, we will use pool and pot experiment under rainproof shed to investigate GS isoenzymes genes expression and activities, leaf chlorophyll and nitrogen content, leaf relative water content, leaf net photosynthesis rate, yield, water and nitrogen use efficiency of drought-stressed wheat after anthesis under different nitrogen level, clarify the effects of different nitrogen supply and assimilation efficiency on drought resistance and yield formation of drought-stressed wheat plants after anthesis, explain the expression pattern of different GS isoenzymes and their relationship with nitrogen assimilation under drought after anthesis. The research results can provide theoretical basis and technical ideas for water-saving cultivation and drought-resistance molecular regulation of wheat.

干旱是影响小麦产量的主要环境障碍之一，维持叶片持绿能力和净光合速率对降低干旱下产量损失至关重要，其与叶片氮含量密切相关，研究表明叶氮量增加能增强植物抗旱性，我们也试验证实小麦幼苗抗旱性与氨同化能力有关，并推测提高氮素供应及同化效率可增强小麦花后抗旱性，但仍缺乏直接的试验证据。谷氨酰胺合成酶(GS)是植物氨同化关键酶，不同GS同工酶GS1和GS2在不同生理条件下有非重叠的作用差异。小麦GS1和GS2基因已被克隆，但其功能和表达调控研究仍有很多空白，对花后干旱的响应至今尚未见报道。本项目采用防雨棚池栽和盆栽试验，通过测定不同施氮水平下花后受旱小麦GS1和GS2基因表达和活性、叶片叶绿素和氮含量、叶片水分和光合特征、产量和水氮利用效率，阐明不同氮素供应及同化效率对小麦花后抗旱性及产量形成的影响，明确GS1和GS2对花后干旱的响应模式及其与氮同化效率的关系，为小麦节水栽培与分子调控提供理论依据。

为阐明不同氮素供应及同化效率对小麦花后抗旱性及产量形成的影响，明确GS1和GS2对花后干旱的响应模式及其与氮同化效率的关系，以河南主推小麦品种为材料，研究了不同水分条件下氮肥供应对小麦产量形成及氮同化的调节作用，主要包括光合特性与产量形成过程、GS同工酶基因表达与氮同化效率。研究发现，限制灌溉条件下，灌浆期灌溉处理的小麦叶片叶绿素含量、净光合速率、气孔导度、蒸腾速率和叶片水分利用率相对较高，旗叶胞间CO2浓度较低；增加施氮量可以增加叶片中叶绿素含量、提高叶片净光合速率、气孔导度、蒸腾速率和叶片水分利用效率，降低旗叶胞间CO2浓度。花后GS活性随灌浆进程逐渐下降，充分灌水和增加施氮量能提高小麦叶片中GS活性；GS1和GS2基因的表达量均随籽粒灌浆呈先升高再下降的趋势，GS2的表达水平下降较快，灌浆后期，GS2基因基本上不再表达，而GS1基因表达量仍处于较高水平；低氮能提高小麦旗叶中GS1和GS2的转录水平，高氮情况下其转录水平降低；限制性灌水下GS1的转录水平较高，拔节期灌溉处理GS2的转录水平较高。以上结果说明，限制灌溉条件下，适当推迟灌水时期和增施氮肥有助于提高小麦灌浆期叶片光合能力，提高产量和水分利用效率；小麦灌浆前期的氮同化效率主要与GS2的基因表达水平有关，而灌浆后期GS1在提高氮同化效率方面起重要作用，GS1的基因表达水平与小麦后期的抗旱性关系可能更密切。上述研究结果可为小麦抗旱分子调控和节水栽培提供可能的理论依据和技术途径。