Photophosphorylation in Scenedesmus in vivo: O2 evolution, ATP pools and transients, and phosphate binding during photoreduction of NO3-, NO2-and CO2 [algae, CO2 fixation, nitrate, nitrite]
1980
Larsson, C.-M. (Stockholm Univ. (Sweden). Inst. of Botany)
The relation between light-induced electron transport with NO('-)(,3), NO('-)(,2) or CO(,2) as acceptors, ATP pools and transients in dark-light-dark transitions, and phosphate uptake was examined in phosphorus-starved cells of Scenedesmus obtusiusculus Chod. Net O(,2) evolution at saturating light was around 6 micro-mol x (mg chlorophyll x h)('-1) in the absence of any acceptor, but reached average rates of 21, 65 and 145 micro-mol x (mg chlorophyll x h)('-1) upon additions of 5 mM KNO(,3), KNO(,2) and KHCO(,3), respectively. The apparent rate of photophosphorylation in transition experiments was only a few percent of the rate calculated from CO(,2)-dependent O(,2) evolution. Blocking non-cyclic electron transport with DCMU inhibited phosphate assimilation, but acceleration of non-cyclic electron flow by addition of NO('-)(,3) or NO('-)(,2) did not stimulate phosphate assimilation as compared to the situation without an acceptor. A functional non-cyclic system might primarily be needed for an efficient shuttle transfer of ATP from the chloroplast to the cytoplasm. An inhibition of the non-cyclic system due to lack of reducible substrates accelerates the cyclic system and thus indicates a regulation mechanism between the two systems
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