Separate Action Spectra for the Two Photochemical Systems of Photosynthesis

Abstract

Transient rates of 02 uptake were measured in the marine green alga Ulva lobata after treatment of the tissue with 3-(3,4-dichlorophenyl)-l, 1-dimethylurea (DCMU). The evolution of O2 was completely suppressed by the inhibitor. The action spectrum for this uptake is believed to represent the activity of the long-wavelength photochemical system (system I). After exposure to high O2 concentrations, the responses of Ulva (untreated with DCMU) suggest an inhibition of system I; subsequent O2 evolution rate determinations yielded an action spectrum possibly resulting from the functioning of the short-wavelength system (system n).