TIP GROWTH OF <i>NEUROSPORA CRASSA </i>IN THE CONDITIONS OF THE RESOURCE DEFICIENCY: IMPAIRMENTS IN THE COHERENCE OF ELONGATION, BRANCHING, AND SEPTATION
With the aid of intracellular fluorescent probes, peculiarities of elongation, branching, septation, and nucleus morphology have been studied in isolated 400-μm-long apical fragments of Neurospora crassa hyphae growing for several hours without the influx of the nutrient materials from the mycelium. We found that: 1) the diameter and growth rate of newly developing branches decreased as compared to intact mycelium (from 10-20 to 6.5 ± 0.4 μm and from 24 ± 1 to 6.7 ± 0.5 μm/min, respectively), but the initial orientation of growth did not change; 2) the branching rhythm was altered; abnormally long internode distances appeared (up to 1471 μm), and the development of some side-branch buds ceased; 3) the character of the septation remained unchanged, as well as the hyphal segment length (68 ± 2 μm). In hyphae growing for 4.5-5.0 h in isolation from the whole mycelium, the distance between the tip and the first septum was 210 ± 15 μm, which was comparable with the respective value in intact mycelium, whereas the mean distance between the growth tip and the first side branch (492 ± 127 μm) and the dispersion of this parameter was considerably higher than in intact mycelium. In branches growing in isolation from the intact mycelium for 1.5-4.5 h, the length of the nucleus-free apical zones near the growth tip (from 5 to 33 μm) and the nucleus morphology were similar to the respective characteristics known for the N. crassa mycelium. The experimental model described here can be used for the investigations of molecular and genetic mechanisms regulating the interactions between intracellular structures involved in the tip growth of N. crassa.