caa a22 4500 445890037 CHVBK 20180317145613.0 cr unu---uuuuu 170323e20111201xx s 000 0 eng 10.1007/s11120-011-9702-9 doi (NATIONALLICENCE)springer-10.1007/s11120-011-9702-9 Oxygen evolution from single- and multiple-turnover light pulses: temporal kinetics of electron transport through PSII in sunflower leaves [Elektronische Daten] [Vello Oja, Hillar Eichelmann, Agu Laisk] Oxygen evolution per single-turnover flash (STF) or multiple-turnover pulse (MTP) was measured with a zirconium O2 analyzer from sunflower leaves at 22°C. STF were generated by Xe arc lamp, MTP by red LED light of up to 18000μmol quantam−2s−1. Ambient O2 concentration was 10-30ppm, STF and MTP were superimposed on far-red background light in order to oxidize plastoquinone (PQ) and randomize S-states. Electron (e−) flow was calculated as 4 times O2 evolution. Q A→Q B electron transport was investigated firing double STF with a delay of 0 to 2ms between the two. Total O2 evolution per two flashes equaled to that from a single flash when the delay was zero and doubled when the delay exceeded 2ms. This trend was fitted with two exponentials with time constants of 0.25 and 0.95ms, equal amplitudes. Illumination with MTP of increasing length resulted in increasing O2 evolution per pulse, which was differentiated with an aim to find the time course of O2 evolution with sub-millisecond resolution. At the highest pulse intensity of 2.9 photonsms−1 per PSII, 3 e− initially accumulated inside PSII and the catalytic rate of PQ reduction was determined from the throughput rate of the fourth and fifth e−. A light response curve for the reduction of completely oxidized PQ was a rectangular hyperbola with the initial slope of 1.2 PSII quanta per e− and V m of 0.6e−ms−1 per PSII. When PQ was gradually reduced during longer MTP, V m decreased proportionally with the fraction of oxidized PQ. It is suggested that the linear kinetics with respect to PQ are apparent, caused by strong product inhibition due to about equal binding constants of PQ and PQH2 to the Q B site. The strong product inhibition is an appropriate mechanism for down-regulation of PSII electron transport in accordance with rate of PQH2 oxidation by cytochrome b6f. Springer Science+Business Media B.V., 2011 Leaves nationallicence Photosystem II nationallicence Oxygen evolution nationallicence Electron transport nationallicence ADC : Analog-to-digital converter nationallicence ETR : Electron transport rate nationallicence F s, F m : Fluorescence yields, steady state and maximum nationallicence FRL : Far-red light nationallicence LED : Light-emitting diode nationallicence MTP : Multiple-turnover pulse nationallicence OEC : Oxygen evolution complex nationallicence PAD, PFD : Photon flux density, absorbed and incident nationallicence PGA : 3-Phosphoglyceric acid nationallicence PQ(H2) : Plastoquinone (reduced) nationallicence PSII : Photosystem II nationallicence RuBP : Ribulose 1,5-bisphosphate nationallicence STF : Single-turnover flash nationallicence Oja Vello Tartu Ülikooli Molekulaar-ja Rakubioloogia Instituut, Riia tn. 23, 51010, Tartu, Estonia aut Eichelmann Hillar Tartu Ülikooli Molekulaar-ja Rakubioloogia Instituut, Riia tn. 23, 51010, Tartu, Estonia aut Laisk Agu Tartu Ülikooli Molekulaar-ja Rakubioloogia Instituut, Riia tn. 23, 51010, Tartu, Estonia aut Photosynthesis Research Springer Netherlands 110/2(2011-12-01), 99-109 0166-8595 110:2<99 2011 110 11120 https://doi.org/10.1007/s11120-011-9702-9 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/s11120-011-9702-9 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Oja Vello Tartu Ülikooli Molekulaar-ja Rakubioloogia Instituut, Riia tn. 23, 51010, Tartu, Estonia aut NATIONALLICENCE 700 1- Eichelmann Hillar Tartu Ülikooli Molekulaar-ja Rakubioloogia Instituut, Riia tn. 23, 51010, Tartu, Estonia aut NATIONALLICENCE 700 1- Laisk Agu Tartu Ülikooli Molekulaar-ja Rakubioloogia Instituut, Riia tn. 23, 51010, Tartu, Estonia aut NATIONALLICENCE 773 0- Photosynthesis Research Springer Netherlands 110/2(2011-12-01), 99-109 0166-8595 110:2<99 2011 110 11120 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer