Light-Induced Ion Movements in Thylakoid Membranes and Isolated LCHII

Abstract

As shown mainly by circular dichroism (CD) spectroscopy, thylakoid membranes and lamellar aggregates of LHCII (the main CM a/b complex associated with photosystem II) contain macrodomains with long range chiral order [1]. These chiral macrodomains are capable to undergo light-induced reversible structural changes, detected as ACD which reflect alterations in the long range order of the chromophores [2]. These changes have been shown to be largely independent of the photochemical activity of membranes [3]. Isolated LHCII have also been shown to possess the capability of undergoing light-induced reversible structural changes (ΔCD) [4]. Both in thylakoids and LHCII the structural changes are accompanied by changes in the fluorescence yield and facilitate the dissipation of excess excitation energy. The physical mechanism of these changes has not been elucidated. It has been proposed that they are driven by thermal fluctuations due to dissipation of excess exciation energy [4, see also Cseh et al., this volume].