STUDIES ON ENHANCED POST-ILLUMINATION RESPIRATION IN MICROALGAE

The extent of enhanced post-illumination respiration (EPIR) has been i nvestigated in a number of microalgae. Respiration rates, as determine d by O-2 consumption, were enhanced (in all but one case) by 50-140% f ollowing pre-exposure to high photon flux compared to rates obtained f or steady-state dark respiration. The extent of EPIR was dependent mor e on photon flux than on duration of exposure, although the latter did have some effect. In Isochrysis galbana and Chaetoceros calcitrens, E PIR effects were also demonstrated using [C-14]CO2 evolution. In I.gal bana, release of CO2 from cells pre-exposed to a period of high photon flux was most rapid from carbohydrate and low-molecular-weight metabo lites. Data obtained from Thalassiosira weisflogii indicate that cells grown at low photon flux are more susceptible to EPIR than those grow n under high photon flux. These results are discussed in the context o f various hypotheses that have been proposed regarding the mechanism o f EPIR effects.