Executive Summary : | Photosynthesis in higher plants is affected by abiotic stresses, such as high light (HL), low temperature, or drought. Nevertheless, plants try to protect photosynthesis by operating different strategies, including photorespiration. Most of these strategies attempt to keep the reactive oxygen species (ROs) levels low. Photorespiration is a multi-step process involving three major organelles: chloroplasts, mitochondria, and peroxisomes. ROs are expected to play a critical role in regulating photorespiration during abiotic and biotic stress. stress conditions, such as HL, which favor photorespiration, can also stimulate chloroplastic cyclic electron transport (CEF) and mitochondrial alternative oxidase (AOX). It is unclear if such up-regulation by HL of photorespiration, CEF, and AOX is simultaneous or if one of these three components responds first. Experiments are necessary to identify the signals originating from CEF or AOX to modulate photorespiration. The present proposal aims at addressing some of these intriguing aspects during the interactions of photorespiration, CEF, and AOX in plant leaves, on exposure to HL. Leaves and mesophyll protoplasts of Arabidopsis thaliana and pea (Pisum sativum) would be used to perform the experiments. The use of pea ensures the availability of large amounts of protoplasts. Experiments are designed to modulate CEF or AOX separately and check the response of photorespiration. similarly, in a reverse approach, photorespiration would either be up-regulated or suppressed to study the consequences on the function/components of CEF or AOX. Then, we would employ suitable mutants of Arabidopsis deficient in selected components of chloroplasts, peroxisomes, and mitochondria and validate the importance of each organelle in the modulation of photorespiration. The planned experiments would reveal which of the three: photorespiration, CEF, and AOX, acts as the master regulator. The results can also provide a proof-of-concept of the dynamic cross-talk between the organelles during photorespiration. |