On the respiratory enhancement in Chlorella pyrenoidosa by blue light.

Previous authours have suggested that the Type I respiratory enhancement in Chlorella was the result of an increased supply of a respiratory substrate or intermediate, or a change in activity of a respiratory enzyme. Our studies with respiratory inhibitors show that the Type I effect is not a general respiratory enhancement, as would be expected from an increase in available substrate, but rather is specifically associated with the tricarboxylic acid cycle and the electron transport chain. The feedback controls on these two processes are such that changes in activities of the component enzymes or in concentrations of carbohydrate intermediates would not be expected to affect the overall respiration rate: an ATP demand is needed to explain the results. A stimulation of chloroplast RNA and protein synthesis by blue light may be the basic mechanism.