Mechanisms of the annual cycling of organic-matrix collagen from spicules of the gorgonian Leptogorgia virgulata

The insoluble organic matrix fraction from the spicules of the gorgonian Leptogorgia virgulata cycles annually. That is, in the summer, this fraction is predominantly collagenous while in the winter, collagen is largely absent. The mechanisms by which cycling occurs have been examined. It appears that spicules become etched and breaches form, probably via acidification and subsequent decalcification. Acidification at the periphery of winter spicules, and presumably subsequent decalcification, has been verified using acridine orange. The internal organic matrix now becomes exposed to the hydrolytic action of such enzymes as acid phosphatase, which is secreted by secondary sclerocytes and scleroblasts. The digestive enzyme acid phosphatase has been localized throughout the year. In the winter, when the collagen content of spicules is lowest, there was strong labeling for acid phosphatase at the periphery of the spicules, suggesting that the enzyme may be involved in the removal of at least some portion of the organic matrix at this season. The level of enzyme activity in the polyps, heaviest in the fall and variable during the rest of the year, probably reflects seasonal changes in the productivity of the coastal waters in which the gorgonians live. Labeling for acid phosphatase was also strong in the winter in the cortical region of the axis. The enzyme may be digesting collagen that was transported to the axis. Labeling for acid phosphatase in the secondary sclerocytes was at a moderate level throughout the year.