抄録
Axonemal microtubules in a large heliozoan, Echinosphaerium nucleofilum strain EC, were examined especially for morphological changes under a highly sensitive polarizing microscope and with an electron microscope. Cold treatment (2°C) caused axopodial degradation to about 10 % of the initial length after 3 h, accompanied by a considerable decrease in the positive birefringence of the intra-axopodial components. Release from the cold treatment resulted in an increment in birefringence and in appearance of 40 nm macrotubules; as the axopodial re-extension proceeded, the diameter of the macrotubules decreased gradually, being replaced by 24 nm micro-tubules in fully-extended axopodia. Colchicine treatment (20 mM, 10 min) caused complete degradation of the axonemal microtubules; no fibrous structures could be detected within the cell body under a polarizing microscope. During the recovery process from colchicine, the cells showed increments in birefringence and decreases in the diameters of tubular structures (macro-tubule-to-microtubule transition). Furthermore, axopodial re-extension was not inhibited by protein synthesis inhibitors (100 μg cycloheximide/ml or 100μg puromycin/ml), but it was inhibited by energy inhibitors (50 μM KCN or 500μM NaN3). The possible mechanisms for macrotubule-to-microtubule transition are discussed mainly on the basis of morphological changes in the tubular structures.
