Yeast, hyphal and pseudohyphal morphologies. (a) Budding yeast cells appear similar to diploid Saccharomyces cerevisiae cells. Shortly after inoculation of unbudded yeast cells, (b) hyphal germ tubes are narrower and more uniform than (e) pseudohyphal buds, which have a constriction at the bud neck. However, it is difficult to obtain a population that consists solely of pseudohyphal cells; in the conditions used, 25% of the cells are hyphal, examples of these are indicated by an arrow plus “Hy.” (c) After 180 minutes, hyphae continue to display parallel-sided walls with no constrictions or branches. (d) Mature hyphal mycelia are shown. (e) Pseudohyphae exhibit morphologies ranging from short pseudohyphae that appear to be polarized yeast cells to (g) two long pseudohyphae that superficially resemble hyphae. (h) The mature pseudohyphal mycelium that results from a homozygous hsl1D mutation is shown. All forms of pseudohyphae superficially resemble hyphae but have constrictions at the positions of septa (arrows) and show regular branching. Growth conditions were as follows: (a) YEPD pH6.0 at 308C; (b, c) YEPD pH6 plus 20% serum, grown at 378C; (d–f) YEPD pH 6.0 at 358C. The images in (f) and (g) were taken from the same culture. (h) Shown is an hsl1D/hsl1D mutant growing in YEPD at 308C. The images in (d) and (h) are of cells stained with Calcofluor white, which stains chitin in the cell walls and septa. All scale bars represent 10 mm (this figure is reproduced with permission from Sudbery et al. [84]).