Photoinhibition of Chlamydomonas reinhardtii in State 1 and State 2

Abstract

The relationship between state transitions and photoinhibition has been studied in Chlamydomonas reinhardtii cells. In State 2, photosystem II activity was more inhibited by light than in State 1. In State 2, however, the D1 subunit was not degraded, whereas a substantial degradation was observed in State 1. These results suggest that photoinhibition occurs via the generation of an intermediate state in which photosystem II is inactive but the D1 protein is still intact. The accumulation of this state is enhanced in State 2, because in this State only cyclic photosynthetic electron transport is active, whereas there is no electron flow between photosystem II and the cytochrome b 6 f complex (Finazzi, G., Furia, A., Barbagallo, R. P., and Forti, G. (1999) Biochim. Biophys. Acta 1413, 117-129). The activity of photosystem I and of cytochrome b 6 f as well as the coupling of thylakoid membranes was not affected by illumination under the same conditions. This allows repairing the damages to photosystem II thanks to cell capacity to maintain a high rate of ATP synthesis (via photosystem I-driven cyclic electron flow). This capacity might represent an important physiological tool in protecting the photosynthetic apparatus from excess of light as well as from other a-biotic stress conditions. The photochemical utilization of absorbed light is a critical step in the photosynthetic process. Because harvesting of light, photochemistry, and electron transfer occur on widely different scales of time, a correct balance among these different processes is required to optimize the efficiency of CO 2 fixation.When light is absorbed in excess of what can actually be utilized by photochemistry, damage to the photosynthetic apparatus may be induced. Impairment of both photosystem I (PSI) 1 (1) and photosystem II (PSII) (2) has been described, and this loss of activity has been termed photoinhibition (3). It has been also shown that the degradation of the PSII reaction center D1 subunit is a major consequence of photoinhibition (2).Some mechanisms contribute to protecting the photosynthetic apparatus from an excess of light (4, 5). The first is the so-called energy-dependent quenching, qE, i.e. the increased thermal dissipation in the PSII antennae that follows the generation of the electrochemical proton gradient across the thylakoid membranes. It is supposed to protect the reaction center from the consequences of a strong illumination by reducing the amount of energy present in the antenna protein complexes (6).The second one (6) is state transitions, a phenomenon that has been discovered in Chlorella pyrenoidosa (7) and in Porphyridium cruentum (8). It is a mechanism to balance light utilization between the two photosystems that is based on the reversible transfer of a fraction of the light-harvesting complex II (LHCII) from PSII to PSI (reviewed in Refs 9 -11). It is also supposed to protect PSII from photoinhibition inasmuch as it can decrease the size of its antenna.The migration of LHCII to PSI (State 1-State 2 transition) re...

Photosystem II antenna phosphorylation-dependent protein diffusion determined by fluorescence correlation spectroscopy

“…We also confirmed that the acceleration of the CBP diffusion occurred in the membranes isolated from the wild-type cells incubated anaerobically in the dark (Fig. S5), which is an alternative method to induce state 2 condition in C. reinhardtii 32. This also verified the acceleration of the CBP diffusion caused by another LHCII phosphorylation-induced condition.…”

Phenotypic Characterization and Hydrogen Production in Chlamydomonas Reinhardtii Qb-Binding D1-Protein Mutants Under Sulfur Starvation: Changes in CHL Fluorescence and Pigment Composition1

“…This drop in the effective quantum yield of PSII had already been noted by Antal et al. (2003), who interpreted it as the consequence of a transition from state 1 to state 2 of the photosynthetic apparatus (Finazzi et al. 2001).…”

Role of the oxidized secondary acceptor QB of Photosystem II in the delayed ‘afterglow’ chlorophyll luminescence

“…This pathway can be induced by warming above 30°C, in the same way as the cyclic electron flow and the heat-induced state 1 to state 2 transition. State 2 appears to switch on the cyclic electron pathway, which would play a protective role against photoinhibition (Finazzi et al 2001(Finazzi et al , 2002. The quinone dark-reduction pathway can be also induced by high light and various stress conditions, modifying the AG emission (Janda et al 1999).…”