Phosphorylation and disassembly of the photosystem II core as an early stage of photoinhibition

Abstract

Abstract. The presence of heterogeneity in phosphorylated PSII core populations in grana membranes of spinach (Spinacia oleracea L.) was previously demonstrated , Biochem. Biophys. Res. Commun. 176, 1298-1304. The effect of photoinhibitory conditions on the distribution of these phosphorylated PSII core populations in thylakoids and PSII particles has been investigated. The sensitivity of the PSII core to strong illumination depended on the phosphorylation state of D 1 and D 2 proteins as well as on the content of the 9-kDa PsbH phosphoprotein. When D 1 and D 2 proteins are under-phosphorylated, the 9-kDa phosphoprotein is tightly bound to the PSII core; thus, a partial protection from photoinhibition is observed. Of the different PSII core populations isolated from membranes photoinhibited for 10 min, the highly phosphorylated populations lack internal antennae CP43 and CP47; perhaps these migrate out to the non-appressed regions of thylakoids. The degradation of the D 1 protein seems to follow the disassembly of the PSII core.

Long-term drought stress induces structural and functional reorganization of photosystem II

“…Four differently phosphorylated PSII core populations, which are interconvertible, are present in grana membranes (Giardi et al , 1994. Thylakoids with highly phosphorylated forms of PSII core result in PSII disassembly within a few minutes of illumination (Giardi 1993a). (iii) In-vivo phosphorylation of D1 is an integral part of light-mediated D1 metabolism (Elich et al 1992).…”

“…Cytochrome b559 was determined from differential oxidized minus reduced spectra at 559 nm (Giardi 1993a). Electron transport activity was measured spectrophotometrically as 2,6-dichlorophenolindophenol (DCPIP) photoreduction at 600 nm with diphenylcarbazide (DPC) as an electron donor (Giardi 1993a).…”

“…Thylakoids, PSII grana and stroma-exposed particles were prepared from control and stressed plants as previously described (Giardi 1993a). For isolation of grana particles, digitonin was used at a final concentration of 0.4%.…”

Dephosphorylation of photosystem II core proteins is light-regulated in vivo.

“…While the function of PSII core protein phosphorylation is less well established, a recent report has implicated these modifications in providing protection against photoinhibition (Harrison and Allen, 1991). Possible mechanisms for this action could involve the regulation of Dl degradation by phosphorylation as a means to prevent the disassembly of PSII (Aro et al, 1992) or the promotion of PsbH protein dissociation from the core by phosphorylation (Giardi, 1993) under photoinhibitory conditions.…”

Nitric oxide donor-mediated inhibition of phosphorylation shows that light-mediated degradation of photosystem II D1 protein and phosphorylation are not tightly linked

“…A number of suggestions have been made for the role of D1 phosphorylation, including: turning oV PS II (or rerouting electron transport) in order to protect the photosystem from damage caused by high light intensity (Yokthongwattana and Melis 2006), downregulating D1 metabolism (Rintamäki et al 1995a) by controlling the timing of its proteolysis (Aro et al 2005), providing protection against photoinhibition (Harrison and Allen 1991), preventing disassembly of PS II (Aro et al 1992), or promoting dissociation of some proteins from the core (Giardi 1993) under photoinhibitory conditions. However, in Spirodela, where light-dependent phosphorylation of D1 is regulated by a circadian clock (Booij-James et al 2002), the greatest amount of phosphorylation occurs hours before maximal light intensity (Booij-James et al 2002), and at intensities well below those saturating for photosynthesis (Jansen et al 1996) or initiation of photoinhibition (Jansen et al 1999).…”