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

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Abstract
The time course of adaptation to changes in growth irradiance was studied in the murine diatom Thalassiosira weisflogii. Irradiance changes were from 72 to 593 .mu.E m-2 s-1 (L .fwdarw. H) and from 593 to 72 .mu.E m-2 s-1 (H .fwdarw. L.). In steady state, high-light (HL) grown cells were characterized by low pigment contents and a low in vivo absorbance. Light saturated photosynthesis, expressed on a per cell basis, was higher for low-light (LL) cells, but on a Chl a basis photosynthesis of HL cells was higher. PSUO2 [Photosynthetic unit based on O2 flash yields] sizes were not significantly different for HL and LL cells. In both transient states the carbohydrate pool was most dynamic and responded fastest to a change in irradiance. It was concluded that the carbohydrate pool serves as an energy and carbon reservoir buffering the cells from changes in irradiance and allowing other cellular properties to adjust to the new situation. The timescales of changes in Chl a cell-1 and photosynthetic activities differed considerably: by a factor of 3 in the L .fwdarw. H transition and by a factor of 30 in the H .fwdarw. L transition. Irradiance transitions did not lead to marked changes in protein cell-1.