Regeneration and mechanisms of secondary attachment in Solieria filiformis (Gigartinales, Rhodophyta)

Abstract

As in most red algae, thallus regeneration in Solieria filiformis (Kützing) Gabrielson provides a means of wound repair in both naturally and experimentally damaged thalli. In cultured explants, regeneration is a polar phenomenon that is characterized by production of endogenous normal buds on the distal cut surfaces and exogenous callus-pads of cortical tissue on the proximal ones. Rhizoid production can occur from both cut surfaces after prolonged forced contact with a substratum. In addition, undamaged apices are able to attach to the substratum by means of internal rhizoidal filaments protruding through the cuticle near the apical cells. Favorable conditions for formation of S. filiformis rhizoids are obtained in contact with penetrable calcareous substrata. Rhizoids outside the thallus behave differently from those inside; their apical cells divide repeatedly and are enclosed in a sheath composed of three layers, the outermost remaining attached to the substratum when the haptera are experimentally removed. After 30–40 d in culture, both haptera and parts of thallus in contact with a substratum become filled with floridean starch granules.