The ultrastructure of carpospore differentiation in the parasitic red alga Levringiella gardneri (Setch.) Kylin

Abstract

Three cytological stages can be recognized during carpospore differentiation in Levringiella gardneri. The youngest stage (stage 1) is identified by a single nucleus surrounded by numerous mitochondria, initiation of dictyosome activity, fibrous vesicles formation, and chloroplasts in the peripheral cytoplasm. During stage 2 striated vesicles are formed within the endoplasmic reticulum, dictyosomes are semicircular in profile and vesicles secreted by dictyosomes contribute either to wall deposition or fibrous vesicle formation. In stage 3 carpospores, striated vesicles degenerate, and straight-profiled dictyosomes secrete numerous cored vesicles. Fibrous vesicles, which are formed throughout carpospore differentiation, release their contents to the outside of the cell and contribute to wall deposition. During the latter part of stage three, however, microtubules appear and these are oriented at right angles to the plasmalemma. A mature carpospore is surrounded by a carpospore wall and a carposporangial wall. One nucleus, an abundance of floridean starch, cored vesicles, mitochondria, chloroplasts and some fibrous vesicles are found in the cytoplasm. Dictyosome activity is low in mature carpospores. Mucilaginous material surrounds all carposporangia and this material is secreted by dictyosomes in secretory cells, located beneath the per icarp cells.