Cyclodextrins, a class of cyclic oligomeric compounds consisting of 68 units of D-glucose, alter the oxygen evolution of photosystem II (PSII) in barley thylakoids as well as chlorophyll a fluorescence induction, i.e., Fv/Fo and Fv/Fm where Fm is the maximal level of fluorescence when all PSII centres are closed, Fo is the minimal level of chlorophyll fluorescence when all PSII centres are open, and Fv is the variable fluorescence (= Fm Fo). The highest Fv/Fm and Fv/Fo values are observed in samples treated with alpha- and beta-cyclodextrins, i.e., 0.618 and 0.629 (Fv/Fm) and 1.617 and 1.667 (Fv/Fo), respectively, whereas in untreated and gamma-cyclodextrin-treated thylakoids, one observes 0.608 and 0.594 (Fv/Fm) and 1.568 and 1.460 (Fv/Fo). This trend is also seen in the oxygen evolution of control and alpha-, beta-, and gamma-cyclodextrin-treated thylakoids, i.e., 183.6, 214.9, 301.7, and 174.0 µmol O2·mg chlorophyll1·h1, respectively. First, the fluorescence induction data indicate that in intact thylakoid membranes, the enhancement of oxygen evolution induced by alpha- and beta-cyclodextrins originates in the opening of blocked photochemical centres in PSII. Second, the results show that the correlation between the oxygen evolution of PSII and chlorophyll a fluorescence induction is a nonlinear phenomenon represented by a Boltzman expression.Key words: chlorophyll, cyclodextrins, fluorescence induction, oxygen evolution, photosystem II, thylakoid membrane.
Rate-limiting steps in the dark-to-light transition of Photosystem II - revealed by chlorophyll-a fluorescence induction
