Characterization of the reversible state of photoinhibition occurring in vitro under anaerobic conditions

Abstract

Thylakoid membranes were subjected to photoinhibitory illumination. The use of oxygen-consuming enzymes to obtain strictly anaerobic conditions showed that while the absence of oxygen is a prerequisite for the formation of a reversibly photoinhibited state, the presence of oxygen is required for the recovery in the dark. The formation of the reversibly photoinhibited state did not protect the thylakoid membranes against irreversible damage. The effects of both bicarbonate and formate were found to be qualitatively different for photoinhibition under strictly anaerobic conditions compared to the effects observed under normal aerobic photoinhibition. It is suggested that there are two different mechanisms of photoinhibition, occurring to different extent under aerobic and anaerobic conditions, respectively, involving QA in both cases, but the QB-site in the former only.

Effects of bicarbonate and oxygen concentration on photoinhibition of thylakoid membranes

“…Also, if the bicarbonate was added after completed illumination, recovery was inhibited (data not shown). A negative influence on the recovery from the reversible photoinhibited state by the addition of 20 mM NaHCO 3 can also be observed for strictly anaerobic conditions created by glucose-oxidase (Sundby and Schi6tt 1992). It has also been observed independently by Hundal and coworkers (Hundal T, personal communication), upon photoinhibition of thylakoid membranes under conditions where a low oxygen content was created by repeated pumping and flushing in a vacuum flask.…”

“…Our conclusion is that it is probably the removal of oxygen that is important as long as the final oxygen concentration is low (below 25/~M) and the time of bubbling is short. Oxygen can be removed also without affecting the carbondioxide content of the suspension at all, by the use of oxygen-consuming enzymes instead of nitrogen bubbling, and this procedure indicates also that removal of oxygen is in itself sufficient to evoke the increased sensitivity to photoinhibition (Krause et al 1985, Trebst et al 1986, Sundby and Schi6tt 1992. However, if the final oxygen concentration is not kept low continuously also after the bubbling treatment, the increased sensitivity to photoinhibition may instead result from the removal of carbondioxide, especially after a more prolonged time of bubbling.…”

“…This 'reversed' effect of NaHCO 3 on photoinhibition at low oxygen conditions is probably explained by an effect on the recovery from the anaerobic photoinhibition. It has recently been shown that anaerobic photoinhibition is different from photoinhibition under aerobic conditions in that the photoinhibited state is only apparently inactivated and during a subsequent dark incubation the activity is recovered (Hundal et al 1990, Kirilovsky and Etienne 1991, Sundby and Schi6tt 1992. In Fig.…”

A macro-tidal freshwater ecosystem recovering from hypereutrophication: the Schelde case study

“…However, the environmental conditions in this hypereutrophied system, may have negatively affected algal growth. There is abundant evidence that extremely low oxygen concentrations negatively affect photosynthesis (Krause et al, 1985;Sundby and Schiött, 1992;Gong et al, 1993;Peckol and Rivers, 1995;Tyystjaervi, 2008) as well as metabolism (Kessler, 1974). Molecular sensors and regulatory genes related to low oxygen concentrations are present in most organisms (Wu, 2002).…”

“…A similar argumentation holds for increased sensitivity to photoinhibition under extreme hypoxia. Algal cells traveling from upper to deeper water layers might first be confronted with high light intensities inducing photoinhibition, and next be transported to dark, hypoxic water layers in which they can not recover from photoinhibitory effects (Sundby and Schiött, 1992;Tyystjaervi, 2008). Finally, a molecular oxygen sensor is probably present in all cells, and regulatory genes related to low oxygen concentrations, downregulating protein synthesis and supressing cell growth during hypoxia to save energy for essential metabolic processes, might also be present in phytoplankton (Wu, 2002).…”