The oxygen-evolving complex: a super catalyst for life on earth, in response to abiotic stresses

Abstract

The oxygen-evolving complex is integrated into photosystem (PSII). An essential part of oxygenic photosynthetic apparatus, embedded in the thylakoid membrane of chloroplasts. The OEC is a super catalyst to split water into molecular oxygen in the presence of light. The OEC consist of four Mn atoms, one Ca atom and five oxygen atoms (CaMn 4 O 5 ) and this cluster is maintained by its surrounding proteins viz., PsbQ, PsbP, PsbO, PsbR. The function of this super catalyst with a high turnover frequency of 500 s −1 in standard condition. Chlorophyll a fluorescence (OJIP transients) are used to understand structural and functional cohesion of photosynthetic apparatus. A further K-peak in OJIP curve reflects damage at the OEC donor site in response to salinity, drought, and high temperature. The decline in performance indices (PI, SFI) also revealed structural damage of photosynthetic apparatus that leads to disruption of electron transport rate under abiotic conditions. This review discusses the structural and function cohesion of the OEC in plant against variable abiotic conditions.

Stem Photosynthesis—A Key Element of Grass Pea (Lathyrus sativus L.) Acclimatisation to Salinity

“…Thus, an efficient and productive photosynthetic apparatus is sine qua non for the life of plants. It consists of three main protein–pigment complexes that are located in the thylakoid membranes, PSII, cytochrome b6f , and PSI, as well as enzymatic proteins that are embedded in the chloroplast stroma [ 74 ]. PSII is composed of three supercomplexes: (1) LHCII—responsible for the perception and transmission of photosynthetic active radiation, (2) PSII RC, where primary charge separation and stabilisation of captured solar energy occurs [ 75 ], and (3) OEC [ 74 ].…”

“…It consists of three main protein–pigment complexes that are located in the thylakoid membranes, PSII, cytochrome b6f , and PSI, as well as enzymatic proteins that are embedded in the chloroplast stroma [ 74 ]. PSII is composed of three supercomplexes: (1) LHCII—responsible for the perception and transmission of photosynthetic active radiation, (2) PSII RC, where primary charge separation and stabilisation of captured solar energy occurs [ 75 ], and (3) OEC [ 74 ]. LHCII contains 70–85% of total Chl, as well as Car pigments, among which lutein and components of the xanthophyll cycle (violaxanthin, anteroxanthin, and zeaxanthin) play major roles in dissipating the excessive amount of absorbed energy, protecting the photosynthetic apparatus against PSII oxidation that could lead to photoinhibition [ 76 , 77 ].…”

“…The disruptions of LET also imply disorders in the formation of a proton gradient between stroma and lumen, leading to a reduction of ATP synthesis, finally reducing the rate of photosynthesis [ 74 ]. Such disturbances were observed in plants that were growing under Ni and Cd stress [ 107 ], as well as in the presence of excess NO 2 – [ 108 ] or NaCl [ 109 , 110 ].…”

“…Non-heme Fe is involved in the electron transport between Q A and Q B . On the one hand, it maintains the appropriate spatial structure between Q A and Q B ; on the other hand, it binds the HCO 3 – ion and, thus, participates in the protonation of Q B 2− [ 74 ]. Zhang et al [ 108 ] believed that the NO 2 – anion binds to non-heme iron instead of the HCO 3 – ion, which inhibits electron transport between Q A and Q B .…”

Overexpression of cytoplasmicSolanum tuberosumGlyceraldehyde 3-phosphate dehydrogenase (GAPDH) gene improves PSII efficiency and alleviates salinity stress inArabidopsis.

“…The energy fluxes per RC (ABS/RC, ETo/RC, and TRo/RC) express the specific functional parameters (Figure 5D), while the energy fluxes per excited cross sections (ABS/ CSo, ETo/CSo, TRo/CSo, and DIo/CSo) represent their comparable phenomenological energy fluxes. Previous studies have shown that salinity reduces the quantum yield of PSII electron transport, the energy available for the RCs, and the efficiency in the capability of PSII for oxygen evolution (Kalaji et al 2011;Gupta 2020). The extrinsic PSII proteins protect the Mn-containing catalytic center that is involved in the oxygen evolution (Sasi et al 2018).…”