Trehalose protects Mn-depleted photosystem 2 preparations against the donor-side photoinhibition

- Trehalose protects Mn-depleted PS2 membranes against donor-side photoinhibition.
- Protection effect of trehalose against photoinhibition of Mn-depleted PS2 requires Mn.
- Trehalose does not protect oxygen-evolving PS2 membranes against photoinhibition.

Recently, it has been shown that the addition of 1 M trehalose leads to the increase of the rate of oxygen photoconsumption associated with activation of electron transport in the reaction center of photosystem 2 (PS2) in Mn-depleted PS2 membranes (apo-WOC-PS2) [37]. In the present work the effect of trehalose on photoinhibition of apo-WOC-PS2 preparations (which are characterized by a high sensitivity to the donor side photoinhibition of PS2) was investigated. The degree of photoinhibition was estimated by the loss of the capability of exogenous electron donor (sodium ascorbate) to reactivate the electron transport (measured by light-induced changes of chlorophyll fluorescence yield (∆F)) in apo-WOC-PS2. It was found that 1 M trehalose enhanced the Mn2 +-dependent suppression of photoinhibition of apo-WOC-PS2: in the presence of trehalose the addition of 0.2 μM Mn2 + (corresponding to 2 Mn2 + per one reaction center) was sufficient for an almost complete suppression of the donor side photoinhibition of the complex. In the absence of trehalose it was necessary to add 100 μM Mn2 + to achieve a similar result. The effect of trehalose was observed during photoinhibition of apo-WOC-PS2 at low (15 μmol photon s− 1 m− 2) and high (200 μmol photon s− 1 m− 2) light intensity. When Mn2 + was replaced by other PS2 electron donors (ferrocyanide, DPC) as well as by Ca2 + the protective effect of trehalose was not observed. It was also found that 1 M trehalose decreased photoinhibition of apo-WOC-PS2 if the samples contained endogenous manganese (1-2 Mn ions per one RC was enough for the maximum protection effect). It is concluded that structural changes in PS2 caused by the addition of trehalose enhance the capability of photochemical reaction centers of apo-WOC-PS2 to accept electrons from manganese (both exogenous and endogenous), which in turn leads to a considerable suppression of the donor side photoinhibition of PS2.