棉花根区盐分差异分布减轻盐害的机理研究

Furrow seeding can induce unequal salt distribution in the root zone of cotton in saline fields, and thus enhances stand establishment and alleviates salt damage. The undying mechanism of salt stress alleviation by unequal salt distribution in the root zone, however, is still unclear. The objective of the present study is to establish unequal salt distribution systems either through furrow seeding in saline fields or split-root system in the greenhouse to study the mechanism of stress-alleviation due to unequal salt distribution at 3 levels. Firstly, the effect of unequal salt distribution on stand establishment and seedling growth in cotton will be studied. On this basis, the physiological mechanism will be investigated by examining dry weight, photosynthetic rate, water use, osmotic stress, ion toxicity and Na+ influx, Na+ efflux and recirculation in cotton plants under equal and unequal salt distribution. Secondly, each root half under unequal salt distribution will be treated with H2O2, NO donor and its inhibitor, and the H2O2, NO and ABA contents as well as Na+ and H+ flux in each root side will be determined. The roles of the signals (H2O2, NO and ABA) in the salt tolerance of cotton under unequal salt distribution will be elucidated. And finally, the roots and leaves of unequal salt distribution treatment (0/200 mM NaCl), equal salt distribution treatment (100/100 mM NaCl) and NaCl free treatment (0/0 mM NaCl) will be used for gene expression analysis through solexa sequencing method. Salt stress related genes and all gene expression differences in roots and leaves under different treatments will be determined by analying cotton EST and solexa sequencing data using bioinformatics methods. As a result, the mechanism of alleviation of salt injury under unequal salt distribution in cotton will be explained at a molecular level.

盐碱地棉花沟种能调节根区盐分形成差异分布，进而减轻盐害、促进成苗，但迄今对根区盐分差异分布减轻棉花盐害的机理尚不清楚。本项目拟通过盐碱地大田沟种和室内分根模拟等方法，创造根区盐分差异分布的实验系统。在观测盐分差异分布对棉花成苗和生长效应的基础上，重点研究干物质积累、光合、水分吸收、渗透胁迫、离子毒害和Na+吸收、外排以及再循环等特征，在生理学层次上揭示根区盐分差异分布减轻棉花盐害的机理；其次，利用H2O2和NO供体及其抑制剂处理盐分差异分布两侧根系，测定根系中H2O2、NO和ABA的含量以及Na+、H+流动性的动态变化，从信号传导角度揭示根区盐分差异分布增强棉株耐盐性的机理；最后，利用表达谱研究盐分差异分布（0/200）和均匀分布(100/100)以及无盐（0/0）对照棉花叶片和根系的基因表达差异，比较不同处理基因表达的差异变化，在分子水平上进一步揭示盐分差异分布减轻棉花盐害的机理。

盐碱地棉花沟种能诱导根区盐分形成差异分布，进而减轻盐害、促进成苗，但迄今对根区盐分差异分布减轻棉花盐害的机理尚不清楚。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减轻棉花盐害的机理。与盐分均匀分布处理相比，盐分差异分布处理促进了棉花生长和水分吸收，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促进低盐侧根系吸收大量水分，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。高盐侧根系诱导低盐侧根系水分吸收和Na+外排的机理为：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，另一方面诱导SOS1基因表达，促进低盐侧根系Na+外排，减轻离子毒害；再一方面诱导低盐侧根系水孔蛋白基因PIP1;7、PIP2;2和PIP2;10表达，促进低盐侧根系吸收大量的水分，减轻渗透胁迫。利用表达谱研究揭示了盐分差异分布减轻棉花盐害的分子机理：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；大量水分吸收基因在高盐侧根系表达降低，但在低盐侧根系表达量上升，这可能是低盐侧根系水分吸收能力上升的重要原因；高盐侧根系大部分养分吸收相关基因的表达量降低，但低盐侧根系表达量升，这可能与低盐侧根系大量吸收养分的原因。综上，盐分差异分布条件下，低盐侧根系水分吸收、养分吸收相关基因大量表达，促使低盐侧根系吸收大量的水分和养分，降低渗透胁迫维持养分平衡；高盐侧根系诱导叶片耐盐关键基因表达，降低叶片中Na+含量，减轻离子毒害。