Abstract
Several strains of Closterium were isolated from the field and aseptically cultured. When spotted on agar plates, cells of some strains spread widely over the plates during cultivation, while cells of the other strains stayed at the inoculation spot, forming a clump. The former type of cells secreted mucilage in a linear fashion. One of these strains, Closterium acerosum was used for studying the mechanism of directional mucilage secretion during phototaxis.
When a plate with actively growing cells was placed under illumination from only one direction, most cells exhibited positive phototaxis. Calcofluor staining showed abundant mucilage ejection from the tip of cells away from the light. To reveal the intracellular processes during this directional mucilage discharge, organelles such as Golgi bodies, ER, and vacuoles were stained and observed by fluorescent microscopy. Further details of the mucilage secretion process were visualized by TEM using the periodic acid-silver hexamine method.
