Mutations Affecting the Trichocysts in <i>Paramecium aurelia.</i> I. Morphology and Description of the Mutants*

Abstract

SYNOPSIS Six types of genic mutants have been isolated. Their phenotypes range from animals with no trichocysts (trichless), to animals with morphologically abnormal trichocysts (football, stubby, pointless, screwy‐cigar), to animals which are incapable of extruding otherwise normal looking trichocysts (nondischarge). The football mutant possesses football‐shaped trichocysts, which, unlike wild‐type trichocysts, do not attach at the cortex. The stubby mutant possesses shorter trichocysts which have a very highly variable morphology. The screwy‐cigar animals have thinner and usually longer trichocysts than those found in wild‐type cells. The trichocysts of the pointless mutant have all the components of the wild‐type organelles but not in their proper relationship. Electron microscopic studies of the mutants have demonstrated that although the morphology of the various mutant trichocysts may differ, their ultrastructure and early developmental stages are comparable to those of trichocysts found in wild type. The mutations are usually pleiotropic, affecting other systems besides trichocysts. The existence of these mutants, particularly trichless, poses some interesting questions regarding the function of trichocysts, and also gives insight into the development of trichocysts.