Seminar/ Colloquium

Title : Photorespiratory metabolism: Not an unavoidable evil but essential to optimize photosynthesis and protect against oxidative stress and photoinhibition.
Speaker : Prof. A.S. Raghavendra, (IoE-Chair Professor, School of Life Sciences) University of Hyderabad.
Date : 06/04/2022, 05:30 PM , Online Mode.

Abstract:

Photosynthesis as well as photorespiration are affected markedly by abiotic as well as biotic stress conditions. The abiotic stress slows down the biochemical reactions of carbon assimilation as well as photochemical activities. Besides anti-oxidant-based systems, plants use additional mechanisms to protect the photosystems from over-excitation. Among these protective components, photorespiration, CEF and AOX appear to be quite crucial. My talk would emphasize that photorespiration is not only a major defence by itself but also up-regulates CEF as well as AOX to provide additional protection of photosynthesis. Once up-regulated, these three processes work in coordination to maintain an optimal redox state of cell and provide ATP for metabolism/protein repair.

Plants are often exposed to oxidative stress, leading to enhanced production of reactive oxygen species (ROS). In response, the cells attempt to down-regulate the production of ROS and also scavenge ROS. The protection by photorespiration of photosynthesis against photoinhibition is well known. Photorespiration can mitigate oxidative stress under conditions of drought/water stress, salinity, low CO2, and chilling.  Such dissipation of excess redox can be either direct (by utilizing ATP, NADH and reduced ferredoxin) or indirect (by sustaining photosynthetic cyclic electron flow, alternate oxidase (AOX) and providing internal CO2 pool).  Even mild disturbance in redox status created by deficiency in ascorbate, alternate oxidase (AOX) or chloroplast NADP-malate dehydrogenase, involved increases in photorespiratory components, such as catalase, glycine, P-protein of glycine decarboxylase complex (GDC). Since the accumulation of excess ROS in plant cell would affect mitochondria as well, the strong interaction between the redox status and photorespiration is not surprising, but is interesting. The photorespiratory reactions in mitochondria and peroxisomes, can perceive the signals of oxidative stress in the form of either ROS or ATP/ADP ratios or mitochondrial thioredoxin status or all of these