DEMONSTRATION OF YEAST BUD SCARS WITH THE ELECTRON MICROSCOPE

Abstract

Ultraviolet photolysis of yeast cells and ascospores was found to clear the cytoplasm of these organisms so as to reveal bud scars as well as internal structures. Saccharomyces cerevisiae was fixed with Bourn''s soln. or osmic acid vapor. The cells were then irradiated at 2537 A for 48 hrs. in the dry state, followed by 48 hrs. irradiation in aqueous suspension. Electron micrographs revealed budding sites irregularly spaced and oriented. The "birth scar" could not be identified. The number of bud scars being an index of the individual cell''s age, it was easy to show that variation in size of individual yeast cells in a culture was the result of the presence of cells of various ages. It was also shown that ascospore formation occurs at any age, asci having been found with few and also with many bud scars. Since the number of bud sites on a cell is geometrically limited it follows that the reproductive life of a budding yeast is also limited. A maximum of 20 bud scars was observed on single cells.