KARYOKINESIS OF SOMATIC NUCLEI OFNEUROSPORA CRASSA: III. THE JUVENILE AND MATURATION CYCLES (FEULGEN AND CRYSTAL VIOLET STAINING)

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Abstract
Somatic karyokinesis in N. crassa can be divided into 3 distinct cycles: 1). Juvenile cycle. This mode of karyokinesis is restricted to young fast growing mycelial material. A ring connecting all the 7 chromosomes is characteristic for this cycle. Prior to division the ring breaks yielding a double stranded nuclear filament which divides longitudinally; 2) Maturation cycle I. This second type of nuclear division occurs prior to the development of macroconidia. The pre-division nucleus develops from a late Juvenile cycle configuration. Division is achieved by longitudinal splitting of a long nuclear filament. The absence of a classical spindle is typical. At least 3 chromosomes carry a single satellite and 1 chromosome possesses 2; 3) Maturation cycle n. This cycle coincides with the formation of microconidia and its divisionary products are incorporated into these structures. The nuclear configurations are associated with the hyphal pore and are extra-ordinarily large in size. Again a filamentous nucleus is constituted which divides in a longitudinal manner. Only 1 daughter nucleus is incorporated into a microconidium, whereas the other daughter filament undergoes subsequent divisions. Centrioles and their division have been studied during Ring phase of the Juvenile cycle. In contrast to classical centrioles, those of somatic nuclei of N. crassa are Feulgen-positive. Based on the descriptive similarities between "Woronin bodies" and the Maturation cycle II nuclei, the authors postulate that they are identical.