PTOX-dependent safety valve does not oxidize P700 during photosynthetic induction in the Arabidopsis pgr5 mutant

• DOI: 10.1093/plphys/kiab541
• Publication Date: 2021-11-15T13:45:52Z
• Authors: Qi Zhou; Caijuan Wang; Hiroshi Yamamoto; Toshiharu Shikanai
• Keywords: P700

Plastid terminal oxidase (PTOX) accepts electrons from plastoquinol to reduce molecular oxygen water. We introduced the gene encoding Chlamydomonas reinhardtii (Cr)PTOX2 into Arabidopsis (Arabidopsis thaliana) wild-type (WT) and proton gradient regulation5 (pgr5) mutant defective in cyclic electron transport around photosystem I (PSI). The accumulation of CrPTOX2 only mildly affected photosynthetic WT background during steady-state photosynthesis but partly complemented induction nonphotochemical quenching (NPQ) pgr5 background. During by actinic light (AL) 130 µmol photons m-2 s-1, high level PSII yield (Y(II)) was induced immediately after onset AL plants accumulating CrPTOX2. NPQ more rapidly transgenic than plants. P700 also oxidized AL. Although does not directly induce a concentration (ΔpH) across thylakoid membrane, coupled reaction generated ΔpH downregulation cytochrome b6f complex. Rapid Y(II) observed In contrast background, lumen acidified CrPTOX2, PGR5 essential for oxidizing P700. addition acidification downregulate complex (donor-side regulation), may be required draining PSI transferring them plastoquinone pool. propose reevaluation contribution this acceptor-side regulation photoprotection PSI.