Nuclear Number And Hyphal Growth

Unlike plant and animal tissues, nuclear division in fungi is not obligatorily coupled to cell division. As a consequence the hypha, even if produced from a uninucleate spore, becomes multinucleate. Some fungi form spores with varying nuclear numbers. For example, the macroconidia of Neurospora crassa contain one to four nuclei per cell. An interesting question is whether the nuclear number influences their rate of germination. Serna and Stadler (1978) measured the DNA content in mithramycin-stained germinating conidia by flow-microfluorimetry as the individual cells passed in a single column through a laser beam. The plot of DNA per 106 cells (x-axis) versus time (y-axis) shows a steady rise over a period of several hours, contrary to the expected step-wise increase if nuclear division was synchronous. Most likely the nuclei in conidia are arrested at various points in the nuclear division cycle. The rate of germination of conidia is not related to nuclear number and the significance of the multinuclear condition remains unknown.

Figure 2.1 Multinuclear mycelium. A portion of Neurospora crassa mycelium stained with Hoechst 33258, a DNA-binding fluorescent dye, to visualize nuclei, and Calcofluor, a chitin-binding dye, to visualize septa.

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