POLYPHOSPHATE AND SILICEOUS GRANULES IN THE GAMETOPHYTES OF THE RED ALGA PORPHYRA PURPUREA (BANGIOPHYCEAE)

Abstract

Variations of the different phosphorylated fractions in tissues of starved and fresh plants of Porphyra purpurea, a representative of the Bangiophyceae, over a 72 hour incubation period in pulse‐enriched seawater (15 μM phosphorus and 25 μM nitrogen) were analyzed and compared to those in Chondrus crispus, a representative of the Florideophyceae, considered the more advanced of the two classes of the Rhodophyta. Differences point towards P. purpurea being a much more metabolically active phosphorus “pump” than C. crispus, with a higher phosphorus turnover rate, in which the orthophosphate fraction is predominant and acid‐soluble and acid‐insoluble polyphosphates are not as significant storage pools. Confirmation of the presence of acid‐insoluble polyphosphates, detected by chemical analyses, in the form of cytoplasmic granules was obtained by transmission electron microscopy and energy dispersive X‐ray microanalysis. The granules in P. purpurea were, however, much smaller (20 to 110 nm in diameter) than those in C. crispus (around 1 μm, but some larger than 2 μm in diameter). Larger granules (290 to 310 nm in diameter) were also observed. Their surface was more uniformly electron‐opaque without the reticulated or globular appearance of typical polyphosphate granules. Energy dispersive X‐ray microanalysis demonstrated that they were siliceous granules. To our knowledge, this is the first report in algae of such structures whose occurrence and metabolic role remain enigmatic.