Photosystem I-dependent cyclic electron transport is important in controlling Photosystem II activity in leaves under conditions of water stress |
| |
Authors: | Eva Katona Spidola Neimanis Gerald Schönknecht Ulrich Heber |
| |
Affiliation: | (1) Julius-von-Sachs-Institut für Biowissenschaften der Universität, Mittlerer Dallenbergweg 64, D-8700 Würzburg, Germany;(2) Present address: Biophics Department, University of Medicine and Pharmacy Carol Davila , 8 Eroii Sanitari Blvd., 76241 Bucharest, Romania |
| |
Abstract: | ![]() Leaves of the C3 plant Brassica oleracea were illuminated with red and/or far-red light of different photon flux densities, with or without additional short pulses of high intensity red light, in air or in an atmosphere containing reduced levels of CO2 and/or oxygen. In the absence of CO2, far-red light increased light scattering, an indicator of the transthylakoid proton gradient, more than red light, although the red and far-red beams were balanced so as to excite Photosystem II to a comparable extent. On red background light, far-red supported a transthylakoid electrical field as indicated by the electrochromic P515 signal. Reducing the oxygen content of the gas phase increased far-red induced light scattering and caused a secondary decrease in the small light scattering signal induced by red light. CO2 inhibited the light-induced scattering responses irrespective of the mode of excitation. Short pulses of high intensity red light given to a background to red and/or far-red light induced appreciable additional light scattering after the flashes only, when CO2 levels were decreased to or below the CO2 compensation point, and when far-red background light was present. While pulse-induced light scattering increased, non-photochemical fluorescence quenching increased and F0 fluorescence decreased indicating increased radiationless dissipation of excitation energy even when the quinone acceptor QA in the reaction center of Photosystem II was largely oxidized. The observations indicate that in the presence of proper redox poising of the chloroplast electron transport chain cyclic electron transport supports a transthylakoid proton gradient which is capable of controlling Photosystem II activity. The data are discussed in relation to protection of the photosynthetic apparatus against photoinactivation.Abbreviations F, FM, F'M, F"M, F0, F'0 chlorophyll fluorescence levels - exc quantum efficiency of excitation energy capture by open Photosystem II - PS II quantum efficiency of electron flow through Photosystem II - P515 field indicating rapid absorbance change peaking at 522 nm - P700 primary donor of Photosystem I - QA primary quinone acceptor in Photosystem II - QN non-photochemical fluorescence quenching - Qq photochemical quenching of chlorophyll fluorescence |
| |
Keywords: | light scattering photoinactivation proton gradient P700 photooxidation quenching of chlorophyll fluorescence redox poising |
本文献已被 SpringerLink 等数据库收录! |
|