INFLUENCE OF PHOSPHORUS STATUS ON THE SEASONAL-VARIATION OF ALKALINE-PHOSPHATASE ACTIVITY IN PORPHYRA UMBILICALIS (L) KUTZING

The influence of internal and external compartments of phosphorus on the alkaline phosphatase activity (APA) of Porphyra umbilicalis during the presence of its gametophytic phase in southern Spain was investigated. The compartments of internal soluble phosphorus were significantly correlated with the percentage cover of Porphyra on the sampling area. APA was inversely correlated with total internal phosphorus and particulate phosphorus. A dynamic model (resembling the cell quota model of Droop) was proposed to relate the enzymatic activity to the internal phosphorus content. According to this model, a maximum APA of 98.5 mu mol p-nitrophenol (pNP) released g.dry wt(-1).h(-1) and a minimum APA of 12.05 mu mol pNP g.dry wt(-1).h(-1) during the gametophytic cycle were estimated. Similarly, a maximum total phosphorus content of 4.2 mg P g.dry wt(-1) and a theoretical minimum total phosphorus content of 0.51 mg P g.dry wt(-1) throughout the gametophytic phase were estimated. The latter value might be close to the subsistence quota for phosphorus; the minimum quota for life.