盐胁迫下小麦根系木质部钠钾离子装载的生理与分子机制研究

Soil salinization is a global issue, elevated Na+ in the soil will disturb the ion homeostasis in plant cells. Among the multiple physiological mechanisms conferring sanlinity tolerance, control of xylem ion loading and regulation of ionic exchange at the xylem-parenchyma boundary have often been named as central to salinity tolerance. However, the mechanism underlying these processes still remain unknown. In this project, a few contrasting wheat genotypes in salinity tolerance will be selected as research materials. The mechanism of xylem ion loading in wheat under salinity stress and the related ion transporters will be investigated with application of the potential second messenger molecules (ABA, H2O2 etc.) and ion-transporter inhibitors, using MIFE technology (non-invasive measurement of specific ion fluxes). Meanwhile, the qRT-PCR will be utilized to determine the transcript level of the related ion transporters (SOS1, HKT1;5, SKOR, etc.). The main objective of this work is to answer the following questions: Is there a difference in the kinetics of xylem ion loading under salinity stress between salt-tolerant and salt-sensitive genotypes? How is this loading controlled, at the physiological level? What is the molecular identity of the transport systems behind this process, and to what extent changes in their expression pattern contribute to this process? The overall goal of this work was to offer a comprehensive insight into mechanisms of ion loading/unloading in the xylem in the context of salinity stress.

土壤中过多的Na+会造成植物细胞内离子平衡紊乱。植物木质部离子装载被认为是最重要的耐盐生理机制之一，但有关木质部钠钾离子装载响应盐胁迫的生理与分子机制尚不清楚。本项目以耐盐性差异显著的小麦品种为试验材料，施以外源信号分子（ABA、H2O2等）和离子转运蛋白抑制剂,利用非损伤微测技术（MIFE）研究盐胁迫下小麦木质部离子装载机理及参与该过程的相关离子转运蛋白。同时采用荧光实时定量PCR技术（qRT-PCR），在小麦根系表皮和中柱中检测差异表达的关键基因（主要靶标为离子转运蛋白，如：SOS1、HKT1;5、SKOR等）响应盐胁迫实时表达变化。旨在回答以下问题：⑴盐胁迫下盐耐受型和盐敏感型小麦品种之间木质部离子装载速率是否存在差异？⑵有哪些相关的信号分子和基因在小麦Na+/K+装载中起主要作用？本项目的研究结果将为阐明小麦根系木质部离子装载的生理机制和分子基础提供有力证据。

为得到可用于不同生育时期小麦耐盐性鉴定的可靠指标，得到耐盐性差异显著的小麦品种，探明外源喷施钾肥对盐胁迫下小麦生长发育及产量形成的调控机理。研究以30个小麦品种为材料，在苗期采用盆栽试验，用150mM NaCl溶液施加处理，对照为自来水浇灌，研究盐胁迫对小麦苗期水分利用、光合生理及渗透离子分配的影响，结果表明叶片K+/Na+比和气孔密度可以作为小麦苗期耐盐性的可靠筛选指标，并得到几对苗期耐盐性差异显著品种，全生育期田间试验以其中5个耐盐差异性显著的春性小麦品种为实验材料，在大丰地区设置非盐逆境 (S0, 播前土壤含盐量 0.770±0.062 g∙kg−1)和盐逆境 (S1, 播前土壤含盐量3.294±0.198 g∙kg−1)两个处理, 研究了盐胁迫对不同耐盐性小麦花后生理特性及产量的影响，结果表明开花期 SPAD值与叶绿素荧光 Fv/Fm可作为耐盐性鉴定快捷可靠的指标, 此外, ‘扬麦 20’在盐碱地中减产幅度最小, 综合表现较好, 适合在大丰地区盐碱地种植。进一步试验研究了外源喷施钾肥对盐胁迫下小麦的调控效应，研究采用盆栽实验，设置盐处理（利用海盐与试验田正常土壤配置得到含盐量在3-3.5g∙kg−1的土壤）及正常（含盐量小于1 g∙kg−1 ）2个盐分处理和外源喷施KH2PO4，研究拔节期外源喷施磷钾肥对盐胁迫下小麦离子积累、物质生产与产量形成的影响。结果表明，拔节期外源喷施磷钾肥可缓解盐胁迫造成的离子失衡，地上部钾钠比含量增加，叶绿素含量增加，减缓了后期叶绿素含量的下降速度，使得地上部干物质积累量、穗粒数、千粒重与产量明显增加。