Polyphosphate and siliceous granules in the macroscopic gametophytes of the red alga Porphyra purpurea (Bangiophyceae, Rhodophyta)

Phosphorylated fractions in tissues of starved and fresh plants of Porphyra purpurea, a representative of the Bangiophyceae, were analyzed over a 48 h incubation period in pulseenriched seawater (15 muM phosphorus and 25 muM nitrogen). Compared to Chondrus crispus, a representative of the structurally and reproductively more complex Florideophyceae, P. purpurea takes up phosphorus much more actively, with a higher turnover rate, in which the orthophosphate fraction is predominant and acidsoluble and acidinsoluble polyphosphates are less significant as storage pools. Presence of cytoplasmic acidinsoluble polyphosphate granules was confirmed by transmission electron microscopy and energy dispersive Xray microanalysis. The granules in P. purpurea were much smaller (20-110 nm in diameter) than those in C. crispus (around 1 mum, but some larger than 2 mum). Larger granules (290-310 nm) were observed in P. purpurea. They were more uniformly electronopaque, without the reticulated/globular appearance of typical polyphosphate granules. Energy dispersive Xray microanalysis demonstrated they were siliceous granules. To our knowledge, this is the first report in algae of such structures whose occurrence and metabolic role remain enigmatic.