title: Quantification of non-QB-reducing centers in leaves using a far-red pre-illumination.
abstract: An alternative approach to quantification of the contribution of non-QB-reducing centers to Chl a fluorescence induction curve is proposed. The experimental protocol consists of a far-red pre-illumination followed by a strong red pulse to determine the fluorescence rise kinetics. The far-red pre-illumination induces an increase in the initial fluorescence level (F(25 micros)) that saturates at low light intensities indicating that no light intensity-dependent accumulation of QA - occurs. Far-red light-dose response curves for the F(25 micros)-increase give no indication of superimposed period-4 oscillations. F(25 micros)-dark-adaptation kinetics following a far-red pre-pulse, reveal two components: a faster one with a half-time of a few seconds and a slower component with a half-time of around 100 s. The faster phase is due to the non-QB-reducing centers that re-open by recombination between QA - and the S-states on the donor side. The slower phase is due to the recombination between QB - and the donor side in active PS II reaction centers. The pre-illumination-induced increase of the F(25 micros)-level represents about 4-5% of the variable fluorescence for pea leaves ( approximately 2.5% equilibrium effect and 1.8-3.0% non-QB-reducing centers). For the other plant species tested these values were very similar. The implications of these values will be discussed.
authors.affiliation: Bioenergetics Laboratory, University of Geneva, Chemin des Embrouchis 10, 1254, Jussy, Geneva, Switzerland. Gert.Schansker@bioen.unige.ch
authors.forename: Gert
authors.initials: G
authors.lastname: Schansker
authors.forename: Reto J
authors.initials: RJ
authors.lastname: Strasser
mesh_terms: D002734:Chlorophyll / Q000737:chemistry / Q000378:metabolism; D000077194:Chlorophyll A; D003116:Color; D004307:Dose-Response Relationship, Radiation; D030681:Ficus / Q000378:metabolism / Q000528:radiation effects; D005453:Fluorescence; D008027:Light; D018532:Pisum sativum / Q000737:chemistry / Q000378:metabolism / Q000528:radiation effects; D010777:Photochemistry; D045332:Photosystem II Protein Complex / Q000737:chemistry / Q000378:metabolism; D018515:Plant Leaves / Q000378:metabolism* / Q000528:radiation effects*; D013045:Species Specificity
chemical_list: D045332:Photosystem II Protein Complex; D002734:Chlorophyll; D000077194:Chlorophyll A