Heterogeneity of the Photochemical Centers in System Ii of Chloroplasts*

Abstract

Abstract— In 3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea (DCMU) poisoned chloroplasts of algae and‘ higher plants the area over the fluorescence induction curve increases with biphasic first order kinetics (Melis and Homann, 1975). Two possibilities are considered to explain the biphasic nature of the area growth. The first is a sequential double reduction of the primary electron acceptor in system II while the second envisages a heterogeneity of its photochemical centers. The kinetic properties of the area growth after firing a single saturating flash proved to be incompatible with the predictions of the “sequential double reduction” model. This conclusion was corroborated by results obtained from a kinetic analysis of the area restoration process in the dark, and an analysis of the partially restored areas. Assuming an existence of a heterogeneous pool of photochemical centers, the growth of the area over the fluorescence curve could be further analyzed to yield two components, a fast a‐component, and a relatively slow β‐component. The kinetic characteristics of these components, and the effect of a short saturating flash on their respective size, led to the conclusion that one type of photochemical center had a faster recombination rate of the photochemically separated charges and was less efficient in trapping excitation energy.

Chlorophyll a fluorescence as a tool to monitor physiological status of plants under abiotic stress conditions

“…Antenna heterogeneity includes variations in antenna size and in connectivity (grouping) of antenna molecules. Based on antenna size, PSII centers have been classified as alpha (a), beta (b), and gamma (c) (Melis and Homann 1976). These differ from each other in life span and number of associated chlorophylls.…”

Energy Transfer and Connectivity in Chloroplasts: Competition between Trapping and Annihilation in Pulsed Fluorescence Induction Experiments

“…When modeling fluorescence induction and S-T annihilation simultaneously, finite antenna sizes have to be taken into account. Moreover, by using this approach, the effects of singlet-triplet annihilation in the presence of heterogeneity in the domain size (R and centers 25,26 ) can also be evaluated. As we will show, singlet-triplet annihilation has a more pronounced effect in larger domains.…”

Analysis of initial chlorophyll fluorescence induction kinetics in chloroplasts in terms of rate constants of donor side quenching release and electron trapping in photosystem II

“…For instance, with a chloroplast density of 10 lg chl/ml, a RCII density of 0.004 and at a photon fluency rate of 0.4 lmol/cm 2 s, k L * 10 ms -1 which is close to that of the quenching release ðk s 1 Þ which we find in the range between 10 and 20 ms -1 . Energy transfer between PSII units, usually denoted as PSII connectivity or grouping (Joliot and Joliot 1964;Strasser 1978), has been recognized for its influence on the fluorescence induction curve in particular the initial phase in the presence of DCMU (Melis and Homann 1976;Geacintov and Breton 1987;Lavergne and Trissl 1995). In the 'classical' concept the relation between the fraction q of centers with Q A -and the variable fluorescence yield is nonlinear (i.e., hyperbolic) if there is energy transfer (connectivity) between units.…”

“…within PSII (Melis and Homann 1976;Joliot and Joliot 1977;Anderson and Melis 1983;Black et al 1986;Graan and Ort 1986;Chylla et al 1987;Govindjee 1990;Lavergne and Leci 1993;Lavergne and Briantais 1996;Lazár et al 2001;Tomek et al 2003;Vredenberg et al 2006); • intersystem energy transfer (connectivity) (Joliot and Joliot 1964;Strasser 1978;Trissl and Lavergne 1995;Bernhardt and Trissl 1999); • quenching of several types (non-photochemical, static, etc. ) and/or by several components ( e.g., P + , Y Z + , Phe -, Q B -, plastoquinone) (Butler 1972;Joliot and Joliot 1973;Vernotte et al 1979;Klimov and Krasnovskii 1981;Krause et al 1982;Hsu and Lee 1995;Kramer et al 1995;Kurreck et al 2000;Koblizek et al 2001;Vasilév and Bruce 1998;Vredenberg 2004;Zhu et al 2005) • a double hit trapping mechanism based on the so-called Three State Trapping Model (TSTM) of PSII (Vredenberg 2000(Vredenberg , 2004).…”