Effects of growth irradiance on the photosynthetic action spectra of the marine dinoflagellate, Glenodinium sp.

Whole cell absorption curves of the marine dinoflagellate Glenodinium sp., cultured at irradiances of 250μW/cm(2) (low light) and 2500μW/cm(2) (high light), were measured and their difference spectrum determined. Absorption by low light grown cells exceeded that of high light grown cells throughout the visible spectrum by a factor which ranged from 2 to 4. The difference spectrum supported the view that increased pigmentation, resulting from low light conditions, was largely due to an increase in cell content of a peridinin-chlorophyll a-protein (PCP) and an unidentified chlorophyll a component of the chloroplast membrane. Photosynthetic action spectrum measurements indicated that chlorophyll a, peridinin, and very likely chlorophyll c, were effective light-harvesting pigments for photosynthesis in both high and low light grown cultures of Glenodinium sp. Comparison of action spectra and absorption spectra suggested that low light grown cells selectively increased cellular absorption in the 480 nm to 560 nm region, and effectively utilized this spectral region for the promotion of oxygen evolution.