Effects of Ultraviolet‐B Radiation on Photosystem II of the Cyanobacterium Synechocystis sp. PCC 6083

Abstract

The effects of ultraviolet-B radiation (280-320 nm) on photosystem I1 of $JneChoCJJStk sp. PCC 6803 were investigated at the functional and structural levels. Loss of oxygen-evolving and electrontransport activity, measured by various techniques including Clark electrode polarography, fluorescence induction and fluorescence relaxation after a single turnover flash, are discussed in terms of two types of damage caused by ultraviolet-B radiation : (a) depletion of the plastoquinone pool ; (b) perturbation and degradation of the D1 protein, with cleavage in the second transmembrane segment. These findings are in full agreement with those obtained, both in vivo and in vitro for higher plants for which a donor-side mechanism involving the water-splitting Mn cluster has been proposed for the main cleavage of the D1 protein. At the structural level, complete disruption of the photosystem 11 core is documented as a consequence of (or in parallel with) degradation of the D1 protein. From this point of view, ultraviolet-Binduced photoinhibition is unlike the visible-induced type and less susceptible to repair by synthesis and reinsertion of new D1 protein Keywords: photosystem 11; cyanobacteria; ultraviolet-B ; damage; D1 protein.Light energy drives photosynthesis, but excess light is potentially harmful to the photosynthetic apparatus of oxygen-evolving organisms [I]. Numerous studies have investigated the molecular mechanisms underlying photoinactivation of the electron transport activity of photosystem 11 (PSII), which is the main target of photoinhibition, and subsequent degradation of PSI1 reaction centre polypeptides D1 and D2. The quite consensual picture which has emerged up to now is that the reaction centre (RC) acceptor side is initially affected during photoinhibition : non-physiological double reduction of first stable acceptor QA promotes its dissociation from the reaction centre D2 protein, thus irreversibly interrupting the electron transport chain [2]. Further excitation of P680 induces the formation of 'P680 through charge recombination of the radical pair P680+-pheophytin- [3]. The reaction of 'P680 with molecular oxygen produces '0, [ 3 ] , which is thought to cause oxidative damage to the D1 protein, thereby promoting its turnover 14, 51. Following inactivation of the acceptor side, or alternatively, inactivation of RC donor side reactions leads to the increased lifetime of highly oxidizing cation radicals such as P680+, Tyr' and Chl' which are thought to be able to damage the D1 protein [6]. It has been shown that damage to the acceptor and donor sides is associated with different degradation patterns of the D1 protein [7, 81. Abbreviations. CIJnd, 2,6-dichloroindophenol; Chl, chlorophyll ; CP43 and CP47, chlorophyll-protein components of the photosystem TI core: Deriphat, lauryl P-D-in~inopropionidate; QA, first stable electron acceptor in photosystem 11; QR, second stable electron acceptor of photosystem 11; PQ, plastoquinoiie-9; PSII, photosystem 11; RC, reaction centre ; STF, single turnover flas...

Determination of Photosystem II Subunits by Matrix-assisted Laser Desorption/Ionization Mass Spectrometry

“…This is demonstrated by the changes induced by exposure of a PSII complex to UV-B radiation or excessive visible light in their MALDI spectra. As expected, a significant decrease in the relative abundance of the peaks due to D1 is observed after visible light stress and of those of both D1 and D2 proteins upon exposure to UV-B, in agreement with previous results (21)(22)(23)(24)(25)(26)(27)(28)(29). The observed significant increase in the number of peaks in the low molecular mass region (data not shown) also indicates the possibility of detecting fragments originating from radiation-induced degradation of PSII proteins.…”

“…Conditions-It is known that the D2 and, to an even greater extent, D1 proteins of higher plants and cyanobacteria are characterized by high turnover and that their degradation rate is increased by UV-B radiation (21)(22)(23)(24)(25) or an excess of photosynthetic active radiation (26 -29). The usual way to reveal these phenomena is to measure the D1 and D2 contents of the thylakoid membrane after exposure to radiation by SDS-PAGE and immunoblotting and then to search for the generated fragments by the same methods.…”

Stoichiometry of the Photosynthetic Apparatus and Phycobilisome Structure of the Cyanobacterium Plectonema boryanum UTEX 485 Are Regulated by Both Light and Temperature

“…The total PQ content was determined as described by Giacometti et al (1996). Quinones were extracted with dietheylether:hexane (1:3 [v/v]) from cells collected on glass fiber filters (GF/C, Whatman, Clifton, NJ).…”

Effects on aquatic ecosystems

“…However, these recent advances continue to underscore the difficulty of using short-term observations to estimate longer-term (days to years) ecological response [2,70,77,[79][80][81]. Solar UV affects growth and reproduction, photosynthetic energy-harvesting enzymes [82][83][84][85][86][87][88] and other cellular proteins, as well as photosynthetic pigment contents [10,[89][90][91][92]. The uptake of ammonium and nitrate is affected by solar radiation in phytoplankton [93][94][95][96], as well as in macroalgae [97].…”