Induction kinetics of photosystem I-activated P700 oxidation in plant leaves and their dependence on pre-energization

Abstract

Abstract-Absorbance changes ΔA 810 were measured in pea (Pisum sativum L., cv. Premium) leaves to track redox transients of chlorophyll P700 during and after irradiation with far red (FR) light under various preil lumination conditions in the absence and presence of inhibitors and protonophorous uncoupler of photosyn thetic electron transport. It was shown that cyclic electron transport (CET) in chloroplasts of pea leaves oper ates at its highest rate after preillumination of leaves with white light and is strongly suppressed after preillu mination with FR light. The FR light induced suppression was partly released during prolonged dark adaptation. Upon FR illumination of dark adapted leaves, the induction of CET was observed, during which CET activity increased to the peak from the low level and then decreased gradually. The kinetics of P700 oxi dation induced by FR light of various intensities in leaves preilluminated with white light were fit to empirical sigmoid curves containing two variables. In leaves treated with a protonophore FCCP, the amplitude of FR light induced changes ΔA 810 was strongly suppressed, indicating that the rate of CET is controlled by the pH gradient across the thylakoid membrane.

Effects of far red light on the induction changes of prompt and delayed fluorescence and the redox state of P700 in Scenedesmus quadricauda

“…3b, 3c) that suppresses Δϕ without hindering ΔрН formation [24]. The earlier formation of ΔрН and the second wave of P700 oxidation are consistent with the notion that photoinduced alkalinization of the stroma stimulates FNR activation [23] resulting in secondary oxidation of P700 [19][20][21].…”

“…After preillumination with FRL, the DL peak at 10-100 ms was substantially lowered, indicating the decrease in electrical component of on thylakoid mem branes. Full oxidation of the plastoquinone pool by preillumination with FRL was reported to inhibit elec trogenesis [18] and cyclic electron flow [19] in higher plant chloroplasts in response to subsequent action of FRL. With this in mind, we assume that FRL preillu mination of algae may have similar effects on electro genesis and cyclic electron transport in the initial period of irradiation with red light.…”

Oxygenic photosynthesis: EPR study of photosynthetic electron transport and oxygen-exchange, an overview

“…Such a multiphase behavior of P 700 + is explained by the lightinduced regulatory processes that take place during the illumination of dark-adapted leaves (for review, see [29][30][31]). Some other examples, illustrating the influence of pre-illumination history on the induction ofP 700 in higher plants, can be found in [32][33][34]. The basic feedback that determines the nonmonotonous kinetics of P 700 oxidation follows: (i) the light-induced activation of the CBC, which accelerates the outflow of electrons from PSI [35−38], (ii) pHdependent attenuation of PSII activity caused by non-photochemical quenching of Chl a excitation in the light-harvesting antenna of PSII [39,40], (iii) deceleration of PQH 2 oxidation within the Cyt b 6 f complex [41][42][43], (iv) the light-induced redistribution of light quanta between PSI and PSII [41], and (v) redistribution of electron fluxes between the alternative pathways of electron transport [32][33][34][44][45][46][47].…”