ZOOSPORE ULTRASTRUCTURE OF POLYMYXA-GRAMINIS (PLASMODIOPHOROMYCETES)

The ultrastructure of the P. graminis Ledingham zoospore is described with emphasis on the flagellar apparatus. The unique characteristics of this zoospore are the 2 kinds of rootlets which extend from the proximal ends of each kinetosome to the plasmalemma. One rootlet consists of a microtubule pair with electron-opaque backing along part of its length which ends abruptly at the plasmalemma. The other rootlet consists of 3 microtubules which, on reaching the plasmalemma, curve around sharply and extend ribbonlike along the side of the zoospoore adjacent to the plasmalemma. This arrangement of rootlets is replicated on the 2nd kinetosome. The kinetosome and transition zone are structurally similar to those in certain protozoa and unlike those found in other groupings of zoosporic fungi or algae.