DELAYED-LIGHT STUDIES ON PHOTOSYNTHETIC ENERGY CONVERSION-IV. EFFECT OF TRIS POISONING, AND OF ITS REVERSAL BY HYDROGEN DONORS, ON THE MILLISECOND EMISSION FROM CHLOROPLASTS*

Abstract— Destruction of the oxygen-evolving activity of chloroplasts by treatment with 0.8 M Tris-HC1 results in an extremely rapid dark decay of millisecond delayed light. Addition of electron acceptors such K₃Fe(CN)₆ or NADP⁺ does not change the decay characteristics of this msec delayed light. Artificial electron donors such as DPC partially restore the msec delayed emission to the slowly decaying situation which is found in control chloroplasts. Addition of electron acceptors to this photochemically competent system results in more rapid decay and in an increase of emission at 1 msec, as in control chloroplasts. We suggest on the basis of the delayed light data that Tris treatment induces a rapid side reaction which uselessly dissipates the oxidizing and reducing power which is stored by Photoreaction II. Artificial electron donors allow the Tris-poisoned photoreaction to store energy long enough for utilization of the energy by normal photosynthetic reactions, as shown by the flattening of the delayed light curves. In the restored system the normal reactions of electron transport are thus able to compete with the Tris-induced side reaction. This interpretation is supported by the finding that the restored system requires higher exciting intensities for saturation of NADP⁺ reduction than the control system.