Destruction of a single chlorophyll is correlated with the photoinhibition of photosystem II with a transiently inactive donor side.

Abstract

Pigments destroyed during photoinhibition of water-splitting photosystem II core complexes from the green alga Chiamydomonas reinhardtii were studied. Under conditions of a transiently inactivated donor side, illumination leads to an irreversible inhibition of the electron transfer at the donor side that is paralleled by the destruction of chlorophylls a absorbing maximally around 674 and 682 nm. The observed stochiometry of 1 + 0.1 destroyed chlorophyll per inhibited photosystem II suggests that chlorophyll destruction could be the primary photodamage causing the inhibition of photosystem II under these conditions.In photosynthesis light energy is converted to chemical energy. However, side reactions can lead to considerable destruction of the photosynthetic apparatus and a concomitant loss of photosynthetic activity in a process called photoinhibition (1). In oxygenic photosynthesis the main target for photoinhibition is photosystem II (PSII) (2). In intact PSII the excited primary donor P680 reduces plastoquinone. The oxidized primary donor P680+ is then reduced by water via an redoxactive tyrosine "Z" (3). In case of a transient malfunction of the water-splitting reaction, P680+ has an extended lifetime during which it can degrade (4) or damage other PSII components, including carotenoids, chlorophylls (Chl), possibly Z, the manganese binding sites, and other amino acids of the PSII proteins (5-10). One or several of these damages result in an irreversible inhibition of the electron transfer from Z to P680+ and hence in an irreversible loss of the water-splitting activity (6,7,(10)(11)(12)(13)(14). Despite many investigations it is still not clear which of the various damages actually causes this inhibition. We investigated this problem by correlating pigment destruction with the loss of oxygen evolving activity.Quantitative observations of pigment destruction in vivo or in grana membranes are difficult due to the high number of pigments per PSII (200-700) (15, 16). PSII reaction center preparations (PSII-RC) contain only 4-6 Chl, 2 pheophytins (pheo), and 1-2 carotenoids (car) per PSII (17-21). Hence, destruction of less than one pigment per PSII can be easily observed in these particles (4,(22)(23)(24). However, since the electron transfer from Z to P680+ is already strongly impaired in freshly isolated PSII-RC (25-27), these particles cannot be used for the investigation of the first irreversibly inactivating reaction of photoinhibition. We therefore used PSII core complexes, which have an intermediate pigment content and are capable of water splitting (28). With these particles it is possible to observe the destruction of less than one Chl per PSII and to measure the loss of water-splitting activity (including the electron transfer from Z to P680+) in parallel.The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact. Experimental ProceduresWater-s...

Non enzymatic antioxidant photoprotection against potential UVBR induced damage in an Antarctic diatom (Thalassiosira sp.)

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Response of holosymbiont pigments from the scleractinian coral Montipora monasteriata to short-term heat stress

“…Allomerization of Chl a occurs when the enolate anion of Chl a is oxidized by free radicals (Hynninen 1991). In vitro, it is inhibited by the presence of ␤-carotene (Hynninen 1991), which is believed to primarily scavenge 1 O 2 (Bumann and Oesterhelt 1995). Although alternative models for allomerization have been presented, it is thought to be principally driven by 1 O 2 as opposed to other reactive oxygen species.…”

Photoinhibition of Photosystem II and photodamage of the oxygen evolving manganese cluster

“…When PSII core complexes were illuminated in the absence of Ca 2+ and Cl − , a chlorophyll molecule was oxidized simultaneously with the inhibition of CaCl 2 -dependent oxygen evolution [93]. The ChlD1 and ChlD2 molecules have the chlorine ring almost parallel with the membrane plane [94] like the chlorophyll first oxidized in donor-side photoinhibition [93], but stable oxidation of these chlorophylls is unlikely because both are part of P 680 + . The EPR signal related to oxidized tyrosine D (a tyrosyl residue of D2 protein) is lost later [84,88], and finally the capacity for primary charge separation and reduction of Q A disappear [83,84].…”