Comparison of the flagellar rootlets and periplast in two marine cryptomonads

Abstract

The flagellar rootlets and the cytoskeletal structures of the furrow–gullet region are described for two marine species of Cryptomonas. The rootlets of the two species are very similar, but are more reduced in C. sp. θ than in C. sp. [Formula: see text]. Four rootlets are present: a compound rootlet made up of a striated component of 60- to 80-nm periodicity overlain by three microtubules which extends anteriorly into the left lobe of the cell, a rhizostyle which descends to the nucleus and the posterior end of the cell, an ascending microtubular rootlet which passes anteriorly into the right lobe of the cell, and a lateral microtubular rootlet which curves around the dorsal side of the contractile vacuole. In C. sp. [Formula: see text], the rhizostyle consists of four winged microtubules; in C. sp.θ, it is reduced to three microtubules which lack wings. In C. sp.[Formula: see text], the ascending rootlet consists of five microtubules; in C. sp. θ, of three microtubules. In C. sp. θ, the lateral rootlet is reduced to a very short remnant. The rootlet systems of these two photosynthetic cryptomonads are similar to, but much reduced in complexity from, that of the leucoplast-containing cryptomonad Chilomonas paramecium. In the vestibulum and furrow–gullet region, the characteristic periplast plates are replaced by a modified periplast in C. sp. θ and a striated rim fiber in C. sp. [Formula: see text].