Photoinhibition of Photosystem I electron transfer activity in isolated Photosystem I preparations with different chlorophyll contents

Abstract

Photoinhibition of the light-induced Photosystem I (PS I) electron transfer activity from the reduced dichlorophenol indophenol to methyl viologen was studied. PS I preparations with Chl/P700 ratios of about 180 (PS I-180), 100 (PS I-100) and 40 (PS I(HA)-40) were isolated from spinach thylakoid membranes by the treatments with Triton X-100, followed by sucrose density gradient centrifugation and hydroxylapatite column chromatography. White light irradiation (1.1 × 10(4)μE m(-2) s(-1)) of PS I-180 for 2 hours bleached 50% of the chlorophyll and caused a 58% decrease in the electron transfer activity with virtually no loss of the primary donor, P700. The flash-induced absorbance change showed the decay phase with a half time of about 10 μs that was attributed to the P700 triplet, suggesting that the photoinhibitory light treatment caused the destruction of the PS I acceptor(s), Fx and possibly A1. PS I-100 was similarly photobleached by the irradiation and the electron transfer activity decreased. There was, however, no apparent photoinhibition of the electron transport activity in PS I(HA)-40. Photoinhibition similar to that seen in PS I-180 also occurred in membrane fragments that were isolated without any detergent from a PS II-deficient mutant strain of the cyanobacterium Synechocystis sp. PCC 6803. PS I-180 was not photoinhibited under anaerobic conditions. The production of superoxide and fatty acid hydroperoxide during white light irradiation was significantly greater in PS I-180 than in PS I(HA)-40. The mechanism of photoinhibition in PS I preparations is discussed in relation to the formation of toxic oxygen molecules.

Light-stress-related changes in the properties of photosystem I

“…In each case, it was observed when chilling-sensitive plants were exposed to a combination of light stress and chilling stress, and the effect could be prevented by a blockage of linear electron transport. With chloroplast fragments, photoinactivation of PS I has also been observed in the absence of chilling stress (Satoh 1970a, b;Sonoike 1995;Baba et al 1996). Our observation of PS I inactivation at room temperature (Table 1 and Herrmann et al 1995) demonstrates that chilling stress is not a basic requirement for this phenomenon (Sonoike 1996).…”

Protective effect of active oxygen scavengers on protein degradation and photochemical function in photosystem I submembrane fractions during light stress

“…This is a heterodimer to which the majority of the core antenna pigments, as well as most of the reaction center cofactors, are bound. In PSI core preparations, strong light exposure induced changes to both reaction‐center proteins [14]. In the present study using submembrane fractions, PsaB was more sensitive to strong light and also produced degradation products (Fig.…”

“…Also, these authors observed that under these conditions toxic hydroxyl radicals were generated. Inactivation of PSI‐mediated electron flow was also reported in isolated PSI core particles such as spinach PSI‐180 and PSI‐100, as well as cyanobacterial PSI membranes exposed to strong light [14]. In PSI core particles illuminated with strong light, damage to the light‐harvesting complex (LHC) and degradation of reaction‐center proteins as well as acceptor side proteins were observed [15].…”

Electrochemistry and photoelectrochemistry of photosystem I adsorbed on hydroxyl-terminated monolayers

“…The PSI suspension in 200 mM phosphate buffer pH 7, containing 1 mM Triton X-100 was stored at À80°C [19]. The extract contained PSI with approximately 40 chlorophyll molecules per P700 center which was characterized for chlorophyll concentration using 80% acetone [20] while the P700 concentration was determined by monitoring the chemically induced absorbance change (recording oxidized minus reduced spectra) as described by Baba et al [6,21].…”