Oxygen Uptake and Evolution Following Monochromatic Flashes in Ulva and an Action Spectrum for System I.

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Abstract
Monochromatic light flashes induced a transient O2 uptake in the marine green alga, Ulva lobata. Maximum uptake occurred with approximately 1/2 second flashes of 705 m[mu] light with an intensity of about 24 x 103 ergs cm-2 sec-1. Shorter wavelengths, higher intensities, or longer flash durations induced an O2 outburst which obscured the uptake. Variations in these parameters can produce transient biphasic responses intermediate between O2 uptake only and O2 production alone. Kinetic observations indicate that the uptake is a dark reaction which appears to follow a photochemical reduction carried out by the long-wavelength pigment system of photosynthesis (system I). The 02 outburst, but not the uptake, was completely inhibited by 10-4 M 3-(3,4-dichlorophenyl)-l,l-dimethylurea (DCMU). With this poison, uptake transients persisted at all visible wavelengths. The transient magnitude varied with wavelength, permitting the determination of an action spectrum for O2 uptake. This action spectrum resembles action spectra for system I determined by other means.
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