Potassium Retention under Salt Stress Is Associated with Natural Variation in Salinity Tolerance among Arabidopsis Accessions

Plants are exposed to various environmental stresses during their life cycle such as salt, drought and cold. Natural variation mediated plant growth adaptation has been employed as an effective approach in response to the diverse environmental cues such as salt stress. However, the molecular mechanism underlying this process is not well understood. In the present study, a collection of 82 Arabidopsis thaliana accessions (ecotypes) was screened with a view to identify variation for salinity tolerance. Seven accessions showed a higher level of tolerance than Col-0. The young seedlings of the tolerant accessions demonstrated a higher K+ content and a lower Na+/K+ ratio when exposed to salinity stress, but its Na+ content was the same as that of Col-0. The K+ transporter genes AtHAK5, AtCHX17 and AtKUP1 were up-regulated significantly in almost all the tolerant accessions, even in the absence of salinity stress. There was little genetic variation or positive transcriptional variation between the selections and Col-0 with respect to Na+-related transporter genes, as AtSOS genes, AtNHX1 and AtHKT1;1. In addition, under salinity stress, these selections accumulated higher compatible solutes and lower reactive oxygen species than did Col-0. Taken together, our results showed that natural variation in salinity tolerance of Arabidopsis seems to have been achieved by the strong capacity of K+ retention.植物在整个生命周期中会遭受多种环境胁迫，例如盐胁迫、干旱与低温胁迫。由自然变异介导的植物生长适应性机制，已被用作应对盐胁迫等多样环境信号的有效策略。然而，该过程背后的分子机制尚未得到充分阐明。本研究收集了82份拟南芥（Arabidopsis thaliana）种质资源（生态型），通过筛选以鉴定耐盐性相关变异。其中7份种质资源的耐盐性显著高于哥伦比亚生态型（Col-0）。在盐胁迫条件下，耐盐种质资源的幼苗表现出更高的钾离子（K+）含量与更低的钠钾比（Na+/K+），但其钠离子（Na+）含量与Col-0并无显著差异。钾离子转运蛋白基因AtHAK5、AtCHX17与AtKUP1在几乎所有耐盐种质资源中均显著上调，甚至在未受盐胁迫的条件下亦是如此。针对钠离子相关转运蛋白基因（如AtSOS家族基因、AtNHX1与AtHKT1;1），筛选得到的耐盐材料与Col-0之间几乎不存在遗传变异或正向转录变异。此外，在盐胁迫条件下，这些耐盐材料积累的相容性溶质更多，而活性氧（ROS）含量则低于Col-0。综上，本研究结果表明，拟南芥耐盐性的自然变异，似乎是通过维持钾离子的高效滞留能力实现的。