Relationship between chlorophyll a fluorescence induction and oxygen evolution in barley (Hordeum vulgare) thylakoids treated with -, -, and -cyclodextrins

Cyclodextrins, a class of cyclic oligomeric compounds consisting of 6–8 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 αand β-cyclodextrins, i.e., 0.618 and 0.629 (Fv/Fm) and 1.617 and 1.667 (Fv/Fo), respectively, whereas in untreated and γ-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 α-, β-, and γ-cyclodextrin-treated thylakoids, i.e., 183.6, 214.9, 301.7, and 174.0 μmol O2·mg chlorophyll–1·h–1, respectively. First, the fluorescence induction data indicate that in intact thylakoid membranes, the enhancement of oxygen evolution induced by αand β-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.