Hyperosmotic stresses represent one of the major constraints that adversely affect plants growth, development, and productivity. In this study, the focus was on early responses to hyperosmotic stress- (NaCl and sorbitol) induced reactive oxygen species (ROS) generation, cytosolic Ca2+ concentration ([Ca2+]cyt) increase, ion fluxes, and mitochondrial potential variations, and on their links in pathways leading to programmed cell death (PCD). By using BY-2 tobacco cells, it was shown that both NaCl- and sorbitol-induced PCD seemed to be dependent on superoxide anion (O2·–) generation by NADPH-oxidase. In the case of NaCl, an early influx of sodium through non-selective cation channels participates in the development of PCD through mitochondrial dysfunction and NADPH-oxidase-dependent O2·– generation. This supports the hypothesis of different pathways in NaCl- and sorbitol-induced cell death. Surprisingly, other shared early responses, such as [Ca2+]cyt increase and singlet oxygen production, do not seem to be involved in PCD.

SummaryIon fluxes are ubiquitous processes in the plant and animal kingdoms, controlled by finetuned regulations of ion channel activity. Yet the mechanism that cells employ to achieve the modification of ion homeostasis at the molecular level still remains unclear. This is especially true when it comes to the mechanisms that lead to cell death.In this study, Arabidopsis thaliana cells were exposed to ozone (O 3 ). Ion flux variations were analyzed by electrophysiological measurements and their transcriptional regulation by RT-PCR. Reactive oxygen species (ROS) generation was quantified by luminescence techniques and caspase-like activities were investigated by laser confocal microscopy.We highlighted the delayed activation of K + outward-rectifying currents after an O 3 -induced oxidative stress leading to programmed cell death (PCD). Caspase-like activities are detected under O 3 exposure and could be decreased by K + channel blocker. Molecular experiments revealed that the sustained activation of K + outward current could be the result of an unexpected O ÁÀ 2 post-transcriptional regulation of the guard cell outward-rectifying K + (GORK) channels. This consists of a likely new mode of regulating the processing of the GORK mRNA, in a ROS-dependent manner, to allow sustained K + effluxes during PCD. These data provide new mechanistic insights into K + channel regulation during an oxidative stress response.