根区盐分差异分布调控棉株体内Na+区隔化分布的机制

Furrow-bed seeding induces non-uniform salinity in saline field, with more accumulation of salts in the ridge and less in the furrow. Our previous studies have indicated that non-uniform salinity could alleviate sodium toxicity through Na+ sequestration by decreasing leaf Na+ content and transporting cytoplasmic Na+ into the vacuole. However, the underlying mechanism of Na+ sequestration at either organic or cellular level under non-uniform salinity in the root zone is still unclear. The objective of the present study is to establish non-uniform salinity distribution systems through furrow-bed seeding in saline fields or through a split-root system in the greenhouse to study the mechanism of Na+ sequestration. Firstly, the physiological mechanism of Na+ sequestration will be investigated by examining Na+ absorption, transport and efflux and Na+ contents in leaf, root, cytoplasm and vacuole. Secondly, the expression pattern of some key genes related to Na+ efflux (SOS1, SOS2, SOS3 and PMA) and vacuolar Na+ sequestration (NHX1, NHX2, NHX6 and AVP) will be determined by real-time PCR analysis to elucidate the molecular mechanism of Na+ sequestration under non-uniform salinity. Finally, each root half under non-uniform salinity will be treated with H2O2, ABA and its inhibitors DPI and fluridone, and the H2O2 and ABA contents and their biosynthesis and catabolism genes in leaf and each root side will be determined. The Na+ efflux, Na+ sequestration and the expression level of Na+ efflux and sequestration related genes in leaf and each root side will also be examined. As a result, the mechanism of H2O2 and ABA regulate Na+ sequestration and Na+ efflux in the low salinity side root will be elucidated.

盐碱地棉花沟畦种植可诱导根区盐分差异分布，能降低棉花叶片Na+含量，并将较多Na+贮存于液泡，产生器官和细泡水平上的Na+区隔化，从而减轻Na+毒害，但迄今对根区盐分差异分布调控盐离子区隔化的机制尚不清楚。本项目拟通过盐碱地大田棉花沟畦种植和室内嫁接分根创造根区盐分差异分布的条件，首先从Na+吸收、运输和外排角度揭示根区盐分差异分布导致盐离子区隔化的机制；其次，分析棉花叶片及根系中Na+外排关键基因（SOS1、SOS2、SOS3和PMA等）和区隔化关键基因（NHX1、NHX2、NHX6和AVP等）的差异表达情况，揭示盐分差异分布导致盐离子区隔化的分子机理；最后，利用H2O2和ABA及其合成抑制剂DPI和fluridone分别处理盐分差异分布两侧根系，测定处理前后叶片和根系Na+、H2O2、ABA含量及相关基因的表达，从信号传导角度揭示H2O2和ABA在调控盐离子区隔化中的作用机制。

盐碱地棉花沟畦种植可诱导根区盐分差异分布，能降低棉花叶片Na+含量，并将较多Na+贮存于液泡，产生器官和细泡水平上的Na+区隔化，从而减轻Na+毒害，但迄今对根区盐分差异分布调控盐离子区隔化的机制尚不清楚。本项目在水培条件下，利用嫁接分根法模拟根区盐分差异分布（0/200 mM NaCl），以均匀分布（100/100 mM NaCl）和无盐胁迫（0/0 mM NaCl）为对照，研究根区盐分差异分布调控盐离子区隔化的机制。与盐分均匀分布处理相比，盐分差异分布处理降低了棉花叶片中的Na+含量，减轻了离子毒害。这主要是因为盐分差异分布能够诱导地上部Na+通过韧皮部向低盐侧根系运输，降低地上部Na+含量和Na+毒害，诱导低盐侧根系（0/200-0）SOS1基因表达，促进Na+外排。高盐侧根系能够诱导低盐侧根系SOS1, SOS2, PMA1和 PMA2基因表达促进Na+外排。高盐侧根系诱导产生耐逆信号传导到地上部，然后地上部信号分子传导到低盐侧根系诱导低盐侧根系ABA合成基因NCED2、NCED3、NCED5和NCED9表达，抑制ABA降解基因CYP707A1、CYP707A2和CYP707A4表达，增加低盐侧根系ABA含量；ABA诱导H2O2合成基因表达，增强低盐侧根系H2O2含量；H2O2一方面抑制ABA合成基因表达，避免低盐侧根系产生过多的ABA，说明根区盐分差异分布能够诱导低盐侧根系产生ABA和H2O2，ABA和H2O2间存在反馈调节作用。施加ABA和H2O2能够诱导SOS1基因表达，促进低盐侧根系Na+外排，但施加ABA和H2O2的抑制剂则抑制SOS1基因表达，降低低盐侧根系Na+外排，说明高盐侧根系可以通过诱导低盐侧根系合成ABA和H2O2促进低盐侧根系Na+外排，减轻棉株离子毒害。利用表达谱研究揭示了盐分差异分布调控盐离子区隔化分布的分子机理：高盐侧根系诱导地上部耐盐关键基因SOS1和NHX1等表达，一方面把地上部叶片中的Na+通过韧皮部转运到低盐侧根系，降低地上部Na+的含量；另一方面将细胞质中Na+离子区隔化到液泡，减轻离子毒害。