Problem:

Inspired by a question asked to me by a classmate, I have the following question about Light-independent (dark phase) reactions in photosynthesis:-

Let us suppose an algae sample was exposed to light for a considerable time so that maximum( if there is a limit) NADPH concentration was achieved. Now if the sample is placed in dark and radioactive ¹?CO? bubbled, will the cell be radiolabelled after some time of bubbling continuously?

I guess the answer depends on the active life of ATP and NADPH , the products of light reaction. If they are considerably stable, such that they are in sufficient concentration for executing Calvin cycle although their production (apart from respiratory ATP production) has ceased due to absence of light. If they are, then the ATP and NADPH produced during the initial exposure period will carry out carbon fixation with radioactive carbon and hence radio labelled sugars will be recoverable from the sample. If not, they will quickly degenerate (by hydrolysis, utilization or likewise) and they will be unable to carry out fixation after some fixed time after stopping the light.

Required:

Question: What, under normal conditions, should be the time after which the light-reaction products are no longer capable of fixing CO? by Calvin cycle?

Question: Will the presence of radioactivity in sugars for the scenario above depend on the species of plant?

Any help would be greatly appreciated!