Cytological phenomena succeeding sporulation in saccharmyces carlsbergensis

Abstract

CONCLUSIONS SEPARATION OF YEAST VEGETATIVE AND YEAST NUCLEI – A COMPARISON The Nucleus in the Living Cell as the Standard. The investigations embodied in this thesis were planned to elucidate the resemblances in the structure of the nuclei of vegetative cells and cysts of Saccharomyces carlsbergensis using living cells with visible nuclei as the standard for comparison. Obviously this would be possible only if one organelle could be identified clearly in the nucleus of the yeast cell. The “homogeneous body” of earlier writers and the vacuole have loomed large in the discussions on the yeast nucleus (Part I of this Thesis). Only one of these can possibly be the real nucleus. The invisibility of the homogeneous body under most physiological conditions (see Part V of this Thesis) necessitated the choice of cells in which both these organelles were visible for investigation of their reactions to fixatives and stains. Evidences were adduced earlier from this laboratory to show that the vacuole is not a permanent structure (Asvatanarayana, 1956a,b), that it disappears on starvation (Asvatanarayana, 1958), that the nucleus is an extra vacuolar structure (Royan, 1956a,b), and that the homogeneous body and the vacuole are unrelated structures (Royan, 1956c). This has been extended and confirmed by a study of the reaction of cells with visible nuclei to vital staining with neutral red (Part VI of this Thesis). While the nucleus remains unstained, there is progressive accumulation of the dye inside the vacuole. The yeast vacuole resembles the plant vacuole in its reactions to neutral red. Being thus a homologue of the plant vacuole, it is only a cytoplasmic inclusion. Further support for such a conclusion is offered by its lack of affinity for haematoxylin and Giemsa and its negative reaction to the Feulgen test. The extra vacuolar body identified as the nucleus of yeast by Linde as far back as 1944 turns out to be the real nucleus.