Tip growth of Neurospora crassa under glucose deprivation

Growth parameters of vegetative hyphae and isolated tip fragments of the mycelial fungus N. crassa were studied after complete substitution of an easily metabolized carbon source (glucose) for a non-metabolized one (sorbitol). The images of growing tips were recorded at 20–30-min intervals. Using original image processing software, geometrical parameters of the hyphal trees (length and number of branches, area of convex polygons circumscribed about the hyphal trees, etc.) were determined and growth characteristics, such as rate of tip elongation (V) and the ratio of the total hyphal length to the number of growing tips (termed “hyphal growth unit”, HGU), were calculated. It is shown that after 4–5-h growth in sorbitol-enriched media growth characteristics of intact hyphae did not differ significantly from the corresponding parameters of hyphae growing in glucose-enriched media. In isolated tip fragments (about 800-μ m long), the values of V were lower than those in intact hyphae but did not depend on the carbon source in the nutrient media. However, in such fragments growing in sorbitol-enriched media the number of branches decreased, while the HGU value and the number of large intracellular vacuoles increased. Staining of cells with a standard chitin probe, Calcofluor White (10 μg/ml), did not reveal any considerable differences in hyphal cell walls and septa in tip fragments grown in the presence of different carbon sources. Possible mechanisms of the dependence of the tip growth parameters on the glucose deficiency are discussed.