Tip growth of Neurospora crassa upon resource shortage: Disturbances of the coordination of elongation, branching, and septation

The characteristics of elongation, branching, septation, and nuclear morphology in hyphal tips (of ~400 μm in length) of the mycelial fungus Neurospora crassa isolated from the mycelium and cultivated for several hours have been investigated using intracellular fluorescent markers. The newly formed branches had the following characteristic features: (1) the predefined orientation was conserved, whereas the diameter decreased (from 10–20 to 6.5 ± 0.4 μm), as did the elongation rate (from 24 ± 1 to 6.7 ± 0.5 μm/min); (2) a disturbed branching pattern with abnormally large internodal distances (up to 1471 μm) and developmental arrest of part of the buds of lateral branches; and (3) a conserved septation pattern and a relatively constant length of hyphal segments (68 ± 2 μm). The size of the nucleus-free zone at the tip (5–33 μm) and the distance between the first septum and the growth point (210 ± 15 μm) in the daughter branches of the isolated fragments were almost the same as in hyphae connected to the mycelium, whereas the average distance between the growth point and the first lateral branch (492 ± 127 μm) and the variability of this parameter were higher in the isolated fragments. The morphology of the nuclei and the size of the nucleus-free zone near the growth point did not differ from those reported for normal vegetative hyphae of N. crassa. The experimental model developed may be used for the elucidation of details of molecular genetic mechanisms that underlie the regulation of interactions between the intracellular structures that provide tip growth of the hyphae in N. crassa.