MICROARCHITECTURE AND ENVELOPE DEVELOPMENT INDYSMORPHOCOCCUS GLOBOSUS(PHACOTACEAE, CHLOROPHYCEAE)1

Abstract

ABSTRACTThe ultrastructure and development of the envelope (lorica) ofDysmorphococcus globosusBold & Starr are described. This is the first detailed characterization of the envelope of a member of the Phacotaceae. The general ultrastructure and cellular organization of the protoplast are similar to that reported for other volvocalean algae. Transmission electron microscopy (TEM) showed the granular and fibrous components of the immature envelope, the sequential deposition of a mineralized layer, and the presence of perforations in the mineralized layer. Iron is incorporated in the mineralized envelope with55Fe labeling. Experiments with59Fe showed an 86% uptake of available iron by cells in culture, with the label localized to the envelope and envelope‐associated mucilage. Envelope formation is the result of the following phenomena: i) secretion of an immature envelope consisting of an outer fibrous layer and an inner granular layer; ii) sequential precipitation of a mineralized component in the inner layer, during which time pores are formed as part of the developmental process; iii) exudation of mucilaginous materials through those pores; iv) localized secretion and subsequent retention of the secretory product giving rise to the pebbled nature of the envelope surface. In living cells, the envelope surface is coated with mucilaginous secretory products that obscure the pores, which were previously reported to be lacking in this species. Results of acetolysis on aplanospores suggest the presence of a sporopollenin inD. globosus.