Reduction of the thylakoid electron transport chain by stromal reductants--evidence for activation of cyclic electron transport upon dark adaptation or under drought.
The reduction of P700(+), the primary electron donor of photosystem I (PSI), following a saturating flash of white light in the presence of the photosystem II (PSII) inhibitor 3-(3.4-dichlorophenyl)-1,1-dimethylurea (DCMU), was examined in barley plants exposed to a variety of conditions. The decay kinetic fitted to a double exponential decay curve, implying the presence of two distinct pools of PSI. A fast component, with a rate constant for decay of around 0.03-0.04 ms(-1) was observed to be sensitive to the duration of illumination. This rate constant was slower than, but comparable to, that observed in non-inhibited samples (i.e. where linear flow was active). It was substantially faster than values typically reported for experiments where PSII activity is inhibited. The magnitude of this component rose in leaves that were dark-adapted or exposed to drought. This component was assigned to PSI centres involved in cyclic electron transport. The remaining slowly decaying P700(+) population (rate constant of around 0.001-0.002 ms(-1)) was assigned to centres normally involved in linear electron transport (but inhibited here because of the presence of DCMU), or inactivated centres involved in the cyclic pathway. Processes that might regulate the relative flux through cyclic electron transport are discussed.
School of Biological Sciences, University of Manchester, 3.614 Stopford Building, Oxford Road, Manchester, M13 9PT, UK.
Alison J
AJ
Golding
Giovanni
G
Finazzi
Giles N
GN
Johnson
D000222:Adaptation, Physiological / Q000502:physiology*; D004237:Diuron / Q000494:pharmacology; D004579:Electron Transport / Q000502:physiology* / Q000528:radiation effects; D001467:Hordeum / Q000378:metabolism*; D008027:Light; D010084:Oxidation-Reduction; D045331:Photosystem I Protein Complex / Q000378:metabolism* / Q000528:radiation effects; D045332:Photosystem II Protein Complex / Q000037:antagonists & inhibitors; D018515:Plant Leaves / Q000378:metabolism; D020524:Thylakoids / Q000378:metabolism*; D014867:Water / Q000378:metabolism
D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; D014867:Water; D004237:Diuron