Growth, breakdown, repair, and rapid contraction of microtubular axopodia in the heliozoan Actinophrys sol

Breakdown of microtubules takes place at the tips of tubules at the distal ends of axopodia when axopodial shortening is induced with colchicine. When small flagellates are captured for ingestion, rapid contraction of axopodia (100 μm in under a second) occurs which apparently involves breakdown of axonemal microtubules. Elongation of a single axopodium after rapid contraction, when all other axopodia are of normal length, proceeds at the same rate as it does when all the axopodia are growing out after microtubule-breakdown induced by cold treatment. In both cases the rate of elongation decreases as axopodia increase in length. Axopodia elastically resist mild bending along their longitudinal axes. They yield nonelastically when more severe bending is applied; bends are formed at certain points along their longitudinal axes. These bends move out along axopodia to their tips.