Comparative phytotoxicity of usnic acid, salicylic acid, cinnamic acid and benzoic acid on photosynthetic apparatus of Chlamydomonas reinhardtii

• Published in: Plant physiology and biochemistry Vol. 128; pp. 1 - 12
• Main Authors: Gao, Yazhi, Liu, Wei, Wang, Xiaoxiong, Yang, Lihua, Han, Su, Chen, Shiguo, Strasser, Reto Jörg, Valverde, Bernal E., Qiang, Sheng
• Format: Journal Article
• Language: English
• Published: France Elsevier Masson SAS 01.07.2018
• Subjects: 820-nm transmission kenetics; Action target; Benzofurans - pharmacology; Benzoic Acid - pharmacology; Chlamydomonas reinhardtii - metabolism; Chlorophyll a fluorescence induction kinetics; Chloroplast Proteins - metabolism; Cinnamates - pharmacology; JIP-Test; Photosynthesis - drug effects; Phytotoxin; Salicylic Acid - pharmacology; Thylakoids - metabolism; Action target; 820-nm transmission kenetics; Phytotoxin; Chlorophyll a fluorescence induction kinetics; JIP-Test
• ISSN: 0981-9428; 1873-2690
• DOI: 10.1016/j.plaphy.2018.04.037

The effects of four phytotoxins usnic acid (UA), salicylic acid (SA), cinnamic acid (CA) and benzoic acid (BA) on photosynthesis of Chlamydomonas reinhardtii were studied in vivo to identify and localise their initial action sites on two photosystems. Our experimental evidence shows that the four phytotoxins have multiple targets in chloroplasts, which mainly lie in photosystem II (PSII), not photosystem I (PSI). They share an original action site by blocking electron transport beyond QA (primary plastoquinone acceptor) at PSII acceptor side since a fast increase of the J-step level is the greatest change in chlorophyll a fluorescence induction kinetics OJIP in C. reinhardtii cells treated with the phytotoxins. UA decreases photosynthetic activity by reducing O2 evolution rate, interrupting PSII electron transport at both the donor and acceptor sides, inactivating the PSII reaction centers (RCs), reducing the content of chlorophylls and carotenoids, destroying the conformation of antenna pigment assemblies, and casuing the degradation of D1/D2 proteins. SA damage to photosynthetic machinery is mainly attributed to inhibition of PSII electron transport beyond QA at the acceptor side, inactivation of the PSII RCs, reduction of chlorophyll content, digestion of thylakoid ploypeptides and destabilization of thylakoid membranes. Both CA and BA affect the photosynthetic process by decreasing PSII electron transport efficiency at the acceptor side and the amount of active PSII RCs. Besides, the initial cause of BA-inhibiting photosynthesis is also assocaited with the O2 evolution rate and the disconnection of some antenna molecules from PSII RCs. [Display omitted] •UA, SA, CA and BA have multiple targets in photosynthetic apparatus, mainly lying in PSII.•Interruption of PSII electron transport beyond QA is their common original inhibiting site.•UA inhibited O2 evolution rate and destroyed antenna pigment assemblies.•SA destroyed thylakoid peptides and reduced chlorophyll content.•BA led to disconnection of PSII antenna molecules and decrease of O2 evolution rate.