Photosynthetic Regulatory Mechanisms for Efficiency and Prevention of Photo‐Oxidative Stress

Abstract

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.

LHCSR3-Type NPQ Prevents Photoinhibition and Slowed Growth under Fluctuating Light in Chlamydomonas reinhardtii

“…Nonphotochemical quenching (NPQ) is a general term for mechanisms that regulate how much light energy is available for photosynthesis [ 3 ]. NPQ is considered important in preventing elevated formation of reactive oxygen species (ROS) that otherwise could occur during excess light absorption [ 4 , 5 ]. The so-called qE component of NPQ, which reduces quantum yields of chlorophyll fluorescence in the light-harvesting antennae, is the dominant thermal dissipation pathway driven by pH changes in the thylakoid lumen [ 6 , 7 , 8 ].…”

Integrative approach reveals new insights into photosynthetic and redox protection in ex vitro tobacco plantlets acclimatization to increasing light intensity

“…Although acclimated to a light intensity higher than 100 µmol photons m -2 s -1 , ex vitro plants displayed some level of oxidative stress also after the low light treatment, showing that acclimation clearly has a cost even if adjusting to lower light intensities. This result was unexpected considering that photooxidative stress is usually associated to conditions of excessive light intensities (Li et al, 2018;Roach & Krieger-Liszkay, 2019). However, several works have shown that short-term low light can also induce oxidative stress, as measured by different indicators (Yu et al, 2016;Li et al, 2017;Zhu et al, 2017), although the molecular mechanisms involved in this specific condition is not as well understood as for high light.…”

Photoprotection in lichens: adaptations of photobionts to high light

“…Despite possessing a variety of light screening pigments, there are times when the amount of light that reaches the photobiont exceeds that which can be used in photosynthesis. This can be problematic because, as discussed above, excess light energy results in elevated levels of ROS produced by chlorophyll ( 1 O 2 ) and electron transport chains (O 2 .− and H 2 O 2 ), thus leading to photo-oxidative damage (Roach & Krieger-Liszkay 2019). Photobionts use several processes to regulate the efficiency at which light energy is used, which are collectively referred to as non-photochemical quenching (NPQ).…”