Role of cyclic electron transport mutations pgrl1 and pgr5 in acclimation process to high light in Chlamydomonas reinhar
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ORIGINAL ARTICLE
Role of cyclic electron transport mutations pgrl1 and pgr5 in acclimation process to high light in Chlamydomonas reinhardtii Ranay Mohan Yadav1 · Sabit Mohammad Aslam1 · Sai Kiran Madireddi1 · Nisha Chouhan1 · Rajagopal Subramanyam1 Received: 4 February 2020 / Accepted: 15 April 2020 © Springer Nature B.V. 2020
Abstract Light is crucial for photosynthesis, but the amount of light that exceeds an organism’s assimilation efficacy can lead to photooxidative damage and even cell death. In Chlamydomonas (C). reinhardtii cyclic electron flow (CEF) is very important for the elicitation of non-photochemical quenching (NPQ) by controlling the acidification of thylakoid lumen. This process requires the cooperation of proton gradient regulation (PGR) proteins, PGRL1 and PGR5. Here, we compared the growth pattern and photosynthetic activity between wild type (137c, t222+) and mutants impaired in CEF (pgrl1 and pgr5) under photoautotrophic and photoheterotrophic conditions. We have observed the discriminative expression of NPQ in the mutants impaired in CEF of pgrl1 and pgr5. The results obtained from the mutants showed reduced cell growth and density, Chl a/b ratio, fluorescence, electron transport rate, and yield of photosystem (PS)II. These mutants have reduced capability to develop a strong NPQ indicating that the role of CEF is very crucial for photoprotection. Moreover, the CEF mutant exhibits increased photosensitivity compared with the wild type. Therefore, we suggest that besides NPQ, the fraction of non-regulated non-photochemical energy loss (NO) also plays a crucial role during high light acclimation despite a low growth rate. This low NPQ rate may be due to less influx of protons coming from the CEF in cases of pgrl1 and pgr5 mutants. These results are discussed in terms of the relative photoprotective benefit, related to the thermal dissipation of excess light in photoautotrophic and photoheterotrophic conditions. Keywords Chlamydomonas reinhardtii · Chlorophyll fluorescence · Cyclic electron transport · High light · Nonphotochemical quenching · Photosystems
Introduction Photosynthesis is the process that can harness solar energy to fix it as chemical energy in a biologically available form. This is a highly regulated process that involves different electron transfer pathways for the generation of ATP and NADPH. The major portion of electron flux required for the generation of ATP and NADPH is provided by linear electron flow (LEF). This process involves the transfer of Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11120-020-00751-w) contains supplementary material, which is available to authorized users. * Rajagopal Subramanyam [email protected] 1
Department of Plant Sciences, School of Life Sciences, University of Hyderabad, Gachibowli, Hyderabad, Telangana 500046, India
electrons from water, the primary electron donor, via photosystem (PS) II, several redox carriers, and PSI to the terminal electron acceptor NADP+. These electro
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