Colchicine-induced expansion ofVaucheria cell apex. Alteration from isotropic to transversally anisotropic growth

The tip-growth ofVaucheria geminata was analyzed. The elemental rate of surface expansion (RERE) at the very apex of this alga cell reaches ca. 100% min⁻¹. The expansion is almost isotropic; i.e. the both meridional and latitudinal components of RERE are almost equal. An antimicrotubular reagent, colchicine, caused expansion at the actively growing cell apex of this alga. This drug did not change the surface expansion rate, but altered the polarity of cell wall expansion from isotropic to transversally anisotropic. The orientation of cell wall microfibrils is random at the apex but axial at the basal cylindrical part of the cell. Colchicine did not change the fluence-response relationship for the first positive phototropism.