Physiological responses of a marine planktonic diatom to transitions in growth irradiance

Abstract

he time course of adaptation to changes in growth irradiance was studied in the marine\rdiatom Thalassiosira weisflogij. Irradiance changes were from 72 to 593 uE m-2 S-' (L + H) and from\r593 to 72 pE S-' (H + L). In steady state, high-light (HL) grown cells were characterized by low\rpigment contents and a low in vivoabsorbance. Light saturated photosynthesis, expressed on a per cell\rbasis, was higher for low-light (LL) cells, but on a Chl a basis photosynthesis of HL cells was higher.\rPSU,, sizes were not significantly different for HL and LL cells. In both transient states the carbohydrate\rpool was most dynamic and responded fastest to a change in ~rradiance. It was concluded that the\rcarbohydrate pool serves as an energy and carbon reservoir buffering the cells from changes in\rirradiance and allowing other cellular properties to adjust to the new situation. The timescales of\rchanges in Chl a cell-' and photosynthetic activities differed considerably: by a factor of 3 in the\rL -, H transition and by a factor of 30 in the H + L transition. Irradiance transitions did not lead to\rmarked changes in protein cell-'.