Uptake kinetics and assimilation of phosphorus by Catenella nipae and Ulva lactuca can be used to indicate ambient phosphate availability

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Journal Article
Journal of Applied Phycology, 2004, 16 (3), pp. 181 - 194
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Uptake, assimilation and compartmentation of phosphate were studied in the opportunist green macroalga Ulva lactuca and the estuarine red algal epiphyte Catenella nipae. The Michaelis-Menten model was used to describe uptake rates of inorganic phosphate (Pi) at different concentrations. Maximum uptake rates (Vmax) of P-starved material exceeded Vmaxof P-enriched material; this difference was greater for C. nipae. Uptake and allocation of phosphorus (P) to internal pools was measured using trichloroacetic acid (TCA) extracts and32P. Both species demonstrated similar assimilation paths: when P-enriched, most32P accumulated as free phosphate. When unenriched,32P was rapidly assimilated into the TCA-insoluble pool. C. nipae consistently assimilated more32P into this pool than U. lactuca, indicating C. nipae has a greater P-storage capacity. In both species,32P release data showed two internal compartments with very different biological half-lives. The rapidly exchanging compartment had a short half-life of ≈2 to 12 min, while the slowly exchanging compartment had a much longer half-life of 12 days in P-starved C. nipae or 4 days in P-starved U. lactuca. In both species, the slowly exchanging compartment accounted for more than 90% of total tissue. U. lactuca and C. nipae responded differently to high external Pi. U. lactuca rapidly took up Pi, transferring this Piinto tissue phosphate and TCA-soluble P in a few hours (≈90% of total P). C. nipae took up Piat lower rates and stored much of this P in less mobile TCA-insoluble forms. Long-term storage of refractory forms of P makes C. nipae a useful bioindicator of the prevailing conditions of Piavailability over at least the previous 7 days, whereas the P-status of U. lactuca may reflect conditions over no more than the previous few hours or days. C. nipae is a more useful bioindicator for P status of estuarine and marine waters than U. lactuca. © 2004 Kluwer Academic Publishers.
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