The Structure and Manner of Division of the Nuclei in the Vegetative Mycelium of Neurospora Crassa

Abstract

BAKERSPIGEL, ALF:XANDEil. (New Mount Sinai Hospital, Toronto, Canada.) The structure and manner of division of the nuclei in the vegetative mycelium of Neurospora crassa.-A;;;-~~:-Jour. Bot. 46131: 180-190. ITJ;;:s. 1959.-A&~c~iption has been--gi~en of the stnl~ture and-;;lanner of division of the nuclei in the conidia and vegetative mycelium of the ascomycete, Neurospora crassa. This is another example of a fungus in which the vegetative nuclei do not appear to divide in the manner of classical mitosis. Instead, as division proceeds, the chromatin forms complexes of chromosomal filaments which then contract. At the end of division the contracted chromatin constricts and pulls rapidly apart without the aid of a visible spindle. Individually recognizable chromosomes were not observed to align themselves on a metaphase plate. In the vegetative mycelium of N. crassa the central body elongates and divides by constriction at the mid region. Thus at the end of division each of the sister nuclei is composed of a portion of the original chromatin and central body. It is suggested that both the elongating central body and the densely stained granule in the chromatin of these nuclei play significant roles during nuclear division. 188 A;\IERI CAN JO UR NAL OF BOTA NY [ Vol. -16 c f l 75 o . J Fig. 75-76. Semidiagramrnatic representation of nuclear division in the vegetative hyphae of N . crassa.-Fig. 75. ( He l· Giemsa technique.) a. An interdivisional nu cleus. b, c. Early division. d-m. Later divisional figures. Not e the double granules in 1, m. n, o. End of division. p, q. Post division, showing 2 sist er nuclei following their separation. Refer to text for description of individual sequences.-Fig. 76. Semi dia grammatic repr esentation of nucl ear divi sion in living vegetative hyphae of N. crassa. a-c. Vari ousl y shaped interdi visional nuclei. d. e. Early divi sional stages. f-h. Later di visional stages. i. End of divi sion . j , k. Post di vision . Th e central bodi es a re evid ent in th e sister nucl ei shown in k. 1. Ma turing sister nucl ei. Duration of di vision : a-f, approximately 6 min. , I-], 2-3 min ., j-I, approximat ely 1 min.Refer to text for description of di visional sequences.

Nuclei in the somatic hyphae of Trichophyton mentagrophytes

“…Figs. 6,8,10,12,13). Nuclear migration in the hyphae of T. mentagrophytes was similar to that reported earlier by Dowding and Bakerspigel (25) and later by the writer in the report by Robinow and Bakerspigel (39).…”

“…It should be emphasized here that similar relationships were observed previously in the somatic hiphae of other imperfect fungi and in the basidiomycete, Sclzizoplzyllurn commune (6,10,12,13). In contrast, nuclei in somatic hyphae of phycomycetes, such as Endogone sphagnophila and species of Saprolegnia, as well as in the ascomycetes Gelasinospora tetrasperma and Neurospora crassa, do not divide simultaneously within the boundaries of a cell (7,8,9,11). Instead, only a few nuclei divide at any one time and even these are in various stages of division.…”

“…In T. mentagrophytes the spindle does not appear to be connected with or arise from the nucleolus. Initially, it is a small body lying at or near the nuclear membrane and it may be similar to that previously described in other fungi as the "heterochromatic granule" (6,8,9).…”

“…appeared to be equal portions of the nucleolus. This type of nucleolus was found in Endogolze sphagnophila in the Saprolegniaceae, in Neurospora crassa, and in Gelasinospora tetrasperma (7,8,9,11). The other type of nucleolus, which was described as being "cast out" at the beginning of division, did not appear to enter directly into division and usually faded from view when sister nuclei had completely separated.…”

MITOSIS IN THE YEAST LIPOMYCES LIPOFER

“…The peculiar behaviour of Lipornyces chromosomes which makes newly formed sister sets move together rather than apart at the end of metaphase is probably also not restricted to this yeast. The bouquets of contracted "chromosomal filaments" which mark the halfway stage of mitosis in Neurospora and Gelasinospora, according to Bakerspigel (3,4), are perhaps the result of similar manoeuvres. The example of Lipom),ces further encourages a fresh look at other fungal nuclei which late in their division assume the shape of a densely chromatinic cord (or two of these parallel and close together).…”