Photosynthetic Oxygen Reduction in Isolated Intact Chloroplasts and Cells in Spinach 1

AUTOR(ES)

Marsho, Thomas V.

RESUMO

The time course of light-induced O2 exchange by isolated intact chloroplasts and cells from spinach was determined under various conditions using isotopically labeled O2 and a mass spectrometer. In dark-adapted chloroplasts and cells supplemented with saturating amounts of bicarbonate, O2 evolution began immediately upon illumination. However, this initial rate of O2 evolution was counterbalanced by a simultaneous increase in the rate of O2 uptake, so that little net O2 was evolved or consumed during the first ∼ 1 minute of illumination. After this induction (lag) phase, the rate of O2 evolution increased 3- to 4-fold while the rate of O2 uptake diminished to a very low level. Inhibition of the Calvin cycle, e.g. with dl-glyceraldehyde or iodoacetamide, had negligible effects on the initial rate of O2 evolution or O2 uptake; both rates were sutained for several minutes, and about balanced so that no net O2 was produced. Uncouplers had an effect similar to that observed with Calvin cycle inhibitors, except that rates of O2 evolution and photoreduction were stimulated 40 to 50%.

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