Kinetic Relationships Between Photosynthesis and Respiration in the Algal Flagellate, Ochromonas Malhamensis.

Studies on the influence of light on respiration have yielded different results with different organisms. In some instances results were interpreted as evidence for light stimulation of respiration (3, 4, 5, 6), in other cases for photoinhibition (8, 13), and in still other examples for a negligible effect (1). With a given species simultaneous measurements of respiratory and photosynthetic 02 metabolism have shown that the influence of light on respiratory processes varied with experimental conditions (3, 4). The fact that conditions have not always been strictly comparable in different investigations probably accounts for some contradictory results. In the preceding paper, which also dealt with the problem of accounting for manifold influences of light -or photosynthetic nietabolism-on respiratorv processes, a very simple model was proposed (figure 1, page 226. In that model photosynthesis is considered as an oxidation-reduction reaction yielding oxidant and reductant at equal rates. The oxidant is the precursor of molecular 02; the reductant serves ultimately to reduce C02. It is assumed that the reductant, but not the oxidant, may react also with components of the respiratory mechanism. Such interaction couldl result in either an increased 02 consumption rate, a decreased C02 production rate, or both. Interaction of some of the reductant with respiratory intermediates would result in diversion of this amount of reductant from its photosynthetic role of C02 assimilation. The photosynthetic-respiratory interactions proposed in the model have several specific consequences which should be experimentally observable. The respiratory quotient ( + C02/-02) Would be decreased and the photosynthetic quotient (+02/-C02) would be increased. The rate of photosynthetic 02 production would he unaffected whether or not the postulated interactions occur, since by assumption the photosynthetic oxidant is not involved. A further consequence of the model is the stoichiometric equivalence of 02 produced in light to the sum: C02 consumed + light-induced extra 02 uptake + light-induced deficit in respiratory C02 production. Perhaps only because of its simplicity, this model wras able to explain quantitatively some light effects on respiration in an arbitrarily selected organism, Ankistrodesmus (4). The present paper describes similar experiments on the physiologically heterodox genus, Ochromonas.