Comparison of the flagellar rootlets and periplast in two marine cryptomonads

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Abstract
The flagellar rootlets and the cytoskeletal structures of the furrow-gullet region are described for 2 marine species of Cryptomonas. The rootlets of the 2 spp. are very similar, but are more reduced in C. sp. .theta. than in C. sp. .vphi.. Four rootlets are present: a compound rootlet made up of a striated component of 60- to 80-nm periodicity overlain by 3 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. .vphi., the rhizostyle consists of 4 winged microtubules; in C. sp. .theta., it is reduced to 3 microtubules which lack wings. In C. sp. .vphi., the ascending rootlet consists of 5 microtubules; in C. sp. .theta., of 3 microtubules. In C. sp. .theta., the lateral rootlet is reduced to a very short remnant. The rootlet systems of these 2 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. .theta. and a striated rim fiber in C. sp. .vphi.