PHOTOSYNTHETIC REGULATORY MECHANISMS FOR EFFICIENCY AND PREVENTION OF PHOTO-OXIDATIVE STRESS

Regulatory mechanisms of photosynthesis affecting light capture, the efficiency of electron transport, and the distribution between linear and alternative electron transport routes are needed to balance energy input with metabolic demands. Rapid fluctuations in light intensity lead transiently to absorption of excess light energy, requiring immediate regulation, whereas adverse environmental conditions over longer-term require acclimation responses. In either case, excitation of photosynthetic pigments beyond metabolic demand and unpoised electron transfer reactions can lead to the generation of reactive oxygen species (ROS). On the one hand, ROS damage the photosynthetic machinery and other macro-molecules, such as thylakoid membranes, contributing to photo-oxidative stress. On the other hand, ROS are needed for acclimation responses since they affect the expression level of responsive genes, as well as exert direct and indirect effects on redox-regulated processes in the chloroplast. In this article, we introduce the photosynthetic complexes, step-by-step and focus on the regulatory mechanisms required to enable photosynthetic efficiency and control levels of ROS production. Finally, we shortly describe the roles of chloroplast-derived ROS in the short-term modulation of photosynthesis and the longer-term acclimation to light stress. Differences in regulatory mechanisms amongst the diversity of Viridiplantae (i.e. green algae to plants) are described.