ИСТИНА

Molecular oxygen plays a crucial role in plant metabolism. O2  is a source of reactive oxygen species (ROS) and oxidative stress. The excessively generated ROS plays both signaling and protective function in mechanically stressed plants. Generation of ROS in microwounded cells is presumably mediated by the plasma membrane NADPH-oxidase that transfers electrons from cytoplasmic NADPH to extracellular oxygen with a concomitant production of ROS, H2 O 2  in particular. Microscopic injuries associated with ROS generation might be accompanied by oxygen concentration changes in the apoplast. Appropriate methods for oxygen measurements on the cellular and subcellular levels are necessary to reveal O2 alterations. In the last decades significant progress has been made in the development of miniature sensors, including oxygen- and ROS-sensitive sensors. Recent invention of nanoscale electrochemical probes provides the opportunity to gain a deeper understanding of oxygen and ROS metabolism upon mechanical stress in plant cells. Our data obtained by applying carbon-filled quartz micropipettes with platinum-coated tips (oxygen nanosensors) showed a considerable drop in oxygen concentration at Chara corallina cell surface in response to microperforation of the cell wall (CW). The oxygen gulp activated by mechanical stress is dependent on stretching of plasma membrane, calcium fluxes across plasmalemma and dynamical rearrangements of micritubules. We tested possible involvement of the suppression of photosynthesis, the enhancement of respiration, and the activation of the plasma membrane NADPH oxidase as an origin of oxygen decline upon CW microwounding. The results provide evidence for major role of plasmalemmal NADPH-oxidase in the discovered local drop of O2 content.