title: Inhibition of photosystems I and II and enhanced back flow of photosystem I electrons in cucumber leaf discs chilled in the light.
abstract: Pre-illumination of cucumber leaf discs at a chilling temperature in low-irradiance white light resulted in accelerated re-reduction of P700(+) [the special Chl pair in the photosystem I (PSI) reaction centre] when the far-red measuring light was turned off. Measurements (in +/- methyl viologen or +/- DCMU conditions) of the re-reduction half time suggest that accelerated re-reduction of P700(+) appeared to be predominantly due to charge recombination and only partly due to reductants sustained by previous cyclic electron flow around PSI. Apparently, charge recombination in PSI was greatly enhanced by inhibition of forward, linear electron flow. Inhibition of PSII electron transport was observed to occur to a lesser extent than that of PSI, but only if the measurement of PSII functionality was free from complications due to downstream accumulation of electrons in pools. We suggest that promotion of controlled charge recombination and cyclic electron flow round PSI during chilling of leaves in the light may partly prevent further damage to both photosystems.
authors.affiliation: Research School of Biological Sciences, Australian National University, GPO Box 475, Canberra, ACT 2601, Australia.
authors.forename: S J
authors.initials: SJ
authors.lastname: Kim
authors.forename: C H
authors.initials: CH
authors.lastname: Lee
authors.forename: A B
authors.initials: AB
authors.lastname: Hope
authors.forename: W S
authors.initials: WS
authors.lastname: Chow
mesh_terms: D002734:Chlorophyll / Q000378:metabolism / Q000528:radiation effects; D002736:Chloroplasts / Q000378:metabolism / Q000528:radiation effects; D003080:Cold Temperature; D018553:Cucumis sativus / Q000378:metabolism* / Q000528:radiation effects; D004563:Electrochemistry; D004579:Electron Transport / Q000528:radiation effects; D004583:Electrons; D066298:In Vitro Techniques; D007700:Kinetics; D008027:Light; D045342:Light-Harvesting Protein Complexes; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism; D045322:Photosynthetic Reaction Center Complex Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism* / Q000528:radiation effects; D045331:Photosystem I Protein Complex; D018515:Plant Leaves / Q000378:metabolism / Q000528:radiation effects
chemical_list: D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D045331:Photosystem I Protein Complex; D002734:Chlorophyll; C001785:chlorophyll P 700; D010100:Oxygen