Potentiation of Photosynthetic Oxygen Evolution in Red Light by Small Quantities of Monochromatic Blue Light

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Abstract
Long-term (up to 3 days) records of O, evolution by the giant green alga, Acetbularia crenulata, were obtained with a stable graphite electrode. Photosynthesis in broad band red light fell in 2 hours to less than 1/2 that provided by white light that initially gave an identical rate. Small doses (< 10-8 Einstein/cm2) of violet or blue radiation than affected a complete, though temporary, restoration of the original rate of photosynthesis. Responses began after a lag of 4-5 minutes, regardless of their magnitude, and in the most favorable instances persisted 4-6 hours after the stimulus. Blue light treatments were effective as flashes as brief as 2.5 seconds, given simultaneously or in sequence with the red measuring light, or as low-intensity continuous irradiations. Blue-light induction of the response was stable over at least 5 minutes of darkness. Chlamydomonas reinhardi and Fucus vesiculosus responded similarly. An action spectrum for the response to short wavelength irradiations indicated 2 peaks of effectiveness, one near 450[mu], and another in the near UV.