Reactive Oxygen Species, Photosynthesis, and Environment in the Regulation of Stomata.

SIGNIFICANCE: Stomata sense the intercellular carbon dioxide (CO2) concentration (Ci) and water availability under changing environmental conditions and adjust their apertures to maintain optimal cellular conditions for photosynthesis. Stomatal movements are regulated by a complex network of signaling cascades where reactive oxygen species (ROS) play a key role as signaling molecules. Recent Advances: Recent research has uncovered several new signaling components involved in CO2- and abscisic acid-triggered guard cell signaling pathways. In addition, we are beginning to understand the complex interactions between different signaling pathways. CRITICAL ISSUES: Plants close their stomata in reaction to stress conditions, such as drought, and the subsequent decrease in Ci leads to ROS production through photorespiration and over-reduction of the chloroplast electron transport chain. This reduces plant growth and thus drought may cause severe yield losses for agriculture especially in arid areas. FUTURE DIRECTIONS: The focus of future research should be drawn toward understanding the interplay between various signaling pathways and how ROS, redox, and hormonal balance changes in space and time. Translating this knowledge from model species to crop plants will help in the development of new drought-resistant crop species with high yields.