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

Abstract

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 pulse-enriched seawater (15 mM phosphorus and 25 mM 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 acid-soluble and acid-insoluble polyphosphates are less significant as storage pools. Presence of cytoplasmic acid-insoluble polyphosphate granules was confirmed by transmission electron microscopy and energy dispersive X-ray microanalysis. The granules in P. purpurea were much smaller (20–110 nm in diameter) than those in C. crispus (around 1 mm, but some larger than 2 mm). Larger granules (290–310 nm) were observed in P. purpurea. They were more uniformly electron-opaque, without the reticulated/globular appearance of typical polyphosphate granules. Energy dispersive X-ray 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.