title: Photosynthetic electron transport activity in heat-treated barley leaves: the role of internal alternative electron donors to photosystem II.
abstract: Electron transport processes were investigated in barley leaves in which the oxygen-evolution was fully inhibited by a heat pulse (48 degrees C, 40 s). Under these circumstances, the K peak (approximately F(400 micros)) appears in the chl a fluorescence (OJIP) transient reflecting partial Q(A) reduction, which is due to a stable charge separation resulting from the donation of one electron by tyrozine Z. Following the K peak additional fluorescence increase (indicating Q(A)(-) accumulation) occurs in the 0.2-2 s time range. Using simultaneous chl a fluorescence and 820 nm transmission measurements it is demonstrated that this Q(A)(-) accumulation is due to naturally occurring alternative electron sources that donate electrons to the donor side of photosystem II. Chl a fluorescence data obtained with 5-ms light pulses (double flashes spaced 2.3-500 ms apart, and trains of several hundred flashes spaced by 100 or 200 ms) show that the electron donation occurs from a large pool with t(1/2) approximately 30 ms. This alternative electron donor is most probably ascorbate.
authors.affiliation: Laboratory of Bioenergetics, University of Geneva, Chemin des Embrouchis 10, CH-1254 Jussy, Geneva, Switzerland. Sztoth@brc.hu
authors.forename: Szilvia Z
authors.initials: SZ
authors.lastname: Tóth
authors.forename: Gert
authors.initials: G
authors.lastname: Schansker
authors.forename: Gyözö
authors.initials: G
authors.lastname: Garab
authors.forename: Reto J
authors.initials: RJ
authors.lastname: Strasser
mesh_terms: D016227:Benzoquinones / Q000378:metabolism*; D001692:Biological Transport; D002734:Chlorophyll / Q000378:metabolism; D000077194:Chlorophyll A; D003624:Darkness; D004579:Electron Transport; D005453:Fluorescence; D001467:Hordeum / Q000187:drug effects / Q000378:metabolism* / Q000528:radiation effects; D006358:Hot Temperature; D008027:Light; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism; D010269:Paraquat / Q000494:pharmacology; D010788:Photosynthesis; D045332:Photosystem II Protein Complex / Q000187:drug effects / Q000378:metabolism* / Q000528:radiation effects; D018515:Plant Leaves / Q000187:drug effects / Q000378:metabolism* / Q000528:radiation effects; D010970:Plastocyanin / Q000378:metabolism; D014443:Tyrosine / Q000378:metabolism
chemical_list: D016227:Benzoquinones; D045332:Photosystem II Protein Complex; D002734:Chlorophyll; C004532:quinone; D014443:Tyrosine; C001785:chlorophyll P 700; D010970:Plastocyanin; D010269:Paraquat; D010100:Oxygen; D000077194:Chlorophyll A