Photoconsumption of molecular oxygen on both donor and acceptor sides of photosystem II in Mn-depleted subchloroplast membrane fragments

Abstract

Oxygen consumption in Mn-depleted photosystem II (PSII) preparations under continuous and pulsed illumination is investigated. It is shown that removal of manganese from the water-oxidizing complex (WOC) by high pH treatment leads to a 6-fold increase in the rate of O(2) photoconsumption. The use of exogenous electron acceptors and donors to PSII shows that in Mn-depleted PSII preparations along with the well-known effect of O(2) photoreduction on the acceptor side of PSII, there is light-induced O(2) consumption on the donor side of PSII (nearly 30% and 70%, respectively). It is suggested that the light-induced O(2) uptake on the donor side of PSII is related to interaction of O(2) with radicals produced by photooxidation of organic molecules. The study of flash-induced O(2) uptake finds that removal of Mn from the WOC leads to O(2) photoconsumption with maximum in the first flash, and its yield is comparable with the yield of O(2) evolution on the third flash measured in the PSII samples before Mn removal. The flash-induced O(2) uptake is drastically (by a factor of 1.8) activated by catalytic concentration (5-10microM, corresponding to 2-4 Mn per RC) of Mn(2+), while at higher concentrations (>100microM) Mn(2+) inhibits the O(2) photoconsumption (like other electron donors: ferrocyanide and diphenylcarbazide). Inhibitory pre-illumination of the Mn-depleted PSII preparations (resulting in the loss of electron donation from Mn(2+)) leads to both suppression of flash-induced O(2) uptake and disappearance of the Mn-induced activation of the O(2) photoconsumption. We assume that the light-induced O(2) uptake in Mn-depleted PSII preparations may reflect not only the negative processes leading to photoinhibition but also possible participation of O(2) or its reactive forms in the formation of the inorganic core of the WOC.

Involvement of molecular oxygen in the donor-side photoinhibition of Mn-depleted photosystem II membranes

“…and Ca 2? at catalytic concentrations (Yanykin et al 2010(Yanykin et al , 2013Khorobrykh et al 2011). In this study, we experimentally verified the suggestion that molecular oxygen (rather than superoxide anion radical formed on the acceptor side of PSII) is directly involved in the donor-side photoinhibition of Mn-depleted PSII membranes.…”

“…In the PSII membranes holding intact WOC, the O 2 photoconsumption rate was very low (2 lmol (mg of Chl) -1 h -1 ), but after removal of Mn from the WOC, the rate was 6-fold higher Yanykin et al 2010). The study of this process showed that in Mn-depleted PSII membrane fragments, the O 2 photoconsumption is associated (about 70 %) with the generation of the long-lived states of P 680…”

“…?Á or TyrZ Á because it was inhibited by diuron and suppressed by exogenous electron donors (Yanykin et al 2010). On the basis of these results, we have proposed that the light-induced O 2 consumption is associated with Photosynth Res the formation of hydroperoxides which proceeds via a radical chain mechanism as follows:…”

“…Previously Yanykin et al 2010), O 2 photoconsumption on the donor side of PSII in Mn-depleted PSII preparations has been revealed. In the PSII membranes holding intact WOC, the O 2 photoconsumption rate was very low (2 lmol (mg of Chl) -1 h -1 ), but after removal of Mn from the WOC, the rate was 6-fold higher Yanykin et al 2010).…”

“…Pre-illumination of Mn-depleted PSII membranes by continuous light led to both the irreversible loss of the capability of PSII donor side to be reactivated by Mn 2? and the suppression of the flashinduced O 2 consumption (Yanykin et al 2010).…”