Abstract
A comparative study of alkaline phosphatase activity (APA) was carried out on repeat samples of representative populations of two species of Gelidium (Rhodophyta), G. latifolium and G. sesquipedale, using p-nitrophenyl phosphate (pNPP) as substrate. The APA kinetics of both species exhibited an apparent negative cooperativity for the hydrolysis of pNPP. Differences were found in phosphatase activities of the two species: G. latifolium showed higher APA per unit biomass and a higher proportion of the phosphate cleaved from the model substrate than G. sesquipedale. Temperature, pH, salinity and external phosphate all had significant effects on the APA of both species. The influence of salinity on APA was due in part to the effects of specific ions (Na+ and Mg2+). No correlation between photon irradiance and APA was observed in G. latifolium, but in G. sesquipedale maximum APA was observed at a relatively low photon irradiance. APA of the two species is discussed with respect to a possible relationship with ecophysiological conditions in nature.
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