Although control of xylem ion loading is essential to confer salinity stress tolerance, specific details behind this process remain elusive. In this work, we compared the kinetics of xylem Na+ and K+ loading between two halophytes (Atriplex lentiformis and quinoa) and two glycophyte (pea and beans) species, to understand the mechanistic basis of the above process. Halophyte plants had high initial amounts of Na+ in the leaf, even when grown in the absence of the salt stress. This was matched by 7-fold higher xylem sap Na+ concentration compared with glycophyte plants. Upon salinity exposure, the xylem sap Na+ concentration increased rapidly but transiently in halophytes, while in glycophytes this increase was much delayed. Electrophysiological experiments using the microelectrode ion flux measuring technique showed that glycophyte plants tend to re-absorb Na+ back into the stele, thus reducing xylem Na+ load at the early stages of salinity exposure. The halophyte plants, however, were capable to release Na+ even in the presence of high Na+ concentrations in the xylem. The presence of hydrogen peroxide (H2O2) [mimicking NaCl stress-induced reactive oxygen species (ROS) accumulation in the root] caused a massive Na+ and Ca2+ uptake into the root stele, while triggering a substantial K+ efflux from the cytosol into apoplast in glycophyte but not halophytes species. The peak in H2O2 production was achieved faster in halophytes (30 min vs 4 h) and was attributed to the increased transcript levels of RbohE. Pharmacological data suggested that non-selective cation channels are unlikely to play a major role in ROS-mediated xylem Na+ loading.

中文翻译：

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盐生植物和藻类植物木质部离子装载的动力学及其调控的比较。

尽管控制木质部离子负载对于赋予盐分胁迫耐受性是必不可少的，但该过程背后的具体细节仍然难以捉摸。在这项工作中，我们比较了两个盐生植物（长叶藜和藜）和两个糖生植物（豌豆和豆）之间木质部Na +和K +的负载动力学，以了解上述过程的机理基础。即使在没有盐胁迫的条件下生长，盐生植物的叶片中Na +的初始含量也很高。与糖原植物相比，木质部汁液Na +浓度高出7倍。盐分暴露后，木质部汁液中Na +的浓度在盐生植物中迅速而短暂地增加，而在糖植物中，这种增加被大大延迟了。使用微电极离子通量测量技术的电生理实验表明，糖类植物倾向于将Na +重新吸收回石碑，从而在盐分暴露的早期减少木质部Na +的负载。然而，即使在木质部中存在高Na +浓度的情况下，盐生植物也能够释放Na +。过氧化氢（H2O2）的存在[模仿NaCl胁迫诱导的根系中活性氧（ROS）的积累]导致根石碑大量吸收Na +和Ca2 +，同时触发了糖浆中从胞质溶胶到质外体的大量K +流出。但不是盐生植物物种。在盐生植物中H2O2产生的峰值达到更快（30分钟对4小时），这归因于RbohE转录水平的增加。