MICROTUBULES OF THE FLAGELLAR APPARATUS ARE ACTIVE DURING PREY CAPTURE IN THE CHRYSOPHYCEAN ALGA EPIPYXIS-PULCHRA

The flagellar apparatus of Epipyxis pulchra (Chrysophceae) and its role in phagotrophy is described. Prior to feeding, the cell elongates forming a basal stalk, and the flagellar apparatus moves away from the contractile vacuole/nucleus complex. In feeding cells the flagellar apparatus consists of a striated rhizoplast, cytoplasmic microtubules nucleated from the short flagellum basal body, three microtubular roots (R1, R3 with tubules a-f, R4) and cytoplasmic microtubules nucleated from R1 and R3 roots. The microtubules of the R3 root split forming a small and a large loop under the short flagellum; the a microtubule forms the inner, smaller loop and the f microtubule forms the outer loop. After looping under the short flagellum, the a and f microtubules join and extend deep into the cell along a complex layered structure involving microtubules, the rhizoplast and a mitochondrion. When a food particle is captured between the flagella, the cell forms a feeding cup to engulf the particle. The rim of the developing cup forms as the distal end of the f microtubule slides up the complex layered structure, increasing the size of its loop under the short flagellum. Vesicles fuse between the loops of the a and f microtubules, increasing the surface area and depth of the cup. When the cup is fully formed, the food particle is moved into the cup. The f tubule returns to its normal position, closing the cup and forming a food vacuole.