The flagellar apparatus in the Chytridiales

Abstract

The flagellar apparatus is described in zoospores of Rhizophydinm chlorogonii, R. constantineani, R. haynaldii, R. laterale, R. patellarium. R. pollinis-pini, R. sphaerotheca, R. subangulosnm, Phlyctochytrium plurigibbosum, Chytridium confervae, C. olla, C. lagenaria, Rhizoclosmatium globosum, and Rluzophlyctis rosea, which are all members of the order Chytridiales. In fine structure, the flagellar apparatus is basically similar to that of fungi in other orders of the class Chytridiomycetes. The characteristics of the flagellar apparatus which are unique to the class are: (1) kinetosome props and associated segment of doublets with a curved extension seen as a hook in thin sections; (2) a spiral structure which connects to the A tubules of the doublets and coils in the core of the transition zone. These characteristics distinguish this class of fungi from the Oomycetes, from algae, protozoa, and other eukaryotes. It is further proposed that six modifications to the flagellar apparatus within the Chytridiales are diagnostic characteristics which could be used for describing subgroupings within the order. These modifications are the presence of a fibrous rhizoplast in some species; presence and form of electron-dense inclusions in the basal area; arrangement of kinetosome-associated microtubules; presence of an electron-dense area in the base of the flagellum; the angle of the nonfunctional centriole to the kinetosome and the presence of a veil-like structure on the side of the nonfunctional centriole. Taxonomic implications of these findings are discussed.