Structure and significance of cruciate flagellar root systems in green algae: Comparative investigations in species ofChlorosarcinopsis (Chlorosarcinales)

Abstract

The ultrastructure of biflagellate zoospores in seven species of the green algaChlorosarcinopsis (Chlorosarcinales) was studied, particularly the cruciate flagellar root system, and a comparative approach was attempted. The seven species constitute four groups on the basis of pyrenoid ultrastructure, presence or absence of a cell envelope covering zoospores, and details of the flagellar root system. Variable structures include root tubule number (4-2-4-2 or 5-2-5-2), association of electron dense material with root tubules and root tubule configurations. Otherwise the root system is similar in all species. Zoospores which lack a cell envelope (three species) show characteristic reorientation of basal bodies with flagellar beat. This results in different images of some basal body associated structures (e.g. distal striated fiber). A fixed basal body orientation was noted in those species where zoospores are covered by a cell envelope. Structural contact of root tubules from root type II (4- or 5-stranded root) with the outer chloroplast membrane in the region of the eyespot was demonstrated for all species. On the basis of some new observations a general description of the cruciate flagellar root system in biflagellate green algae is given and a new nomenclature is offered. Taxonomic implications and functional aspects of cruciate flagellar root systems in biflagellate green algae are discussed.