These micrographs were taken from an SEM survey of N. crassa morphological mutants undertaken by Matthew L. Springer as part of his doctoral dissertation research in the laboratory of Dr. Charles Yanofsky.
Those pictures that were deemed to be pertinant to the research project were published; many others were not. However, one or two representative pictures of each mutant studied are now available for viewing and downloading from this web site.
We hope that this can serve as a resource for investigators whose research has led them to examine any of these mutants, and who would like to get an idea of what the morphology of these mutants is like on an SEM level, even if the pictures were never published published in a journal. Each image is available in the form of a JPEG file at roughly 300 dpi if viewed at 4 x 5 inches. The on-line images were all saved at 640 X 480 to make them more easily downloaded. Each original file is approximately 200-500 K. If you need one of these, please contact the FGSC.

A brief comment is included for each picture. For more information on the mutants and the developmental stages referenced, see Perkins et al. (1982) Microbiol. Rev. 46:426-570; Springer and Yanofsky (1989) Genes Dev. 3:559-571; or Springer (1993) BioEssays 15:365-374, and the references listed therein. (Individual mutants may appear in more recent references; a literature search is in order.) Briefly, the asexual developmental stages referenced occur in the following order: aerial hyphal growth, minor constriction stage (budding of initial 2-10 proconidia), major constriction stage (budding of subsequent proconidia), septation, separation of conidia.

74A;The representative wild-type strain. Picture (a) shows a representative region of proconidial chains before septation and separation. Picture (b) shows a macroconidiophore after septation and some separation has occured. Some regions of aerial hyphae that gave rise to the conidiophore are also visible.

acon-2;aconidiate-2. This temperature-sensitive mutant is blocked before the minor constriction stage when grown at non-permissive temperature.

acon-3;aconidiate-3. This mutant is blocked before the major constriction stage and makes unusually long minor constriction chains, which can occasionally be observed to revert to hyphal growth.

adh;adherant. Macroconidiophores are short and stunted. There is frequently an unusually large number of arthroconidia (short separated segments derived from aerial hyphae).

csp-1;conidial separation-1. Conidial separation is inefficient, resulting in long chains of proconidia.

csp-2;conidial separation-2. Conidial separation is almost non-existant, resulting in very long chains of proconidia. Calcofluor staining of proconidial chains reveals very thick crosswalls that lack the usual ultrastructure.

cwl;crosswall-less. The lack of hyphal septa results in extremely fragile hypha. A single rupture in the cell wall can lead to a deflation of the entire hypha, as shown in the picture.

fl;fluffy (P allele). This aconidial mutant is blocked before the major constriction stage, but it possesses fewer minor constriction chains than acon-3.

fld;fluffyoid. Blocked before the minor constriction stage. This mutant has temperature-sensitive properties in that it can be forced to conidiate a little bit under carbon-limiting conditions at 25˚C but not at 34˚C.

fr;frost. Macroconidiophores are absent and are replaced by aerial hyphal structures resembling coral. These structures and the normal aerial hyphae nearby undergo extra septation and arthroconidiation quite efficiently.

gran;granular. This mutant exhibits a biphasic conidial phenotype. During the early stages of conidiation (possibly corresponding to minor constriction budding), interconidial junctions are wide and relatively unformed (picture a). During later stages of budding (possible corresponding to major constriction budding), interconidial junctions are very tight and much more plentiful than normal (picture b); hence, free conidia stained with Calcofluor exhibit 5-10 "bud scars" instead of the usual 2-3.

mat;mat. Chosen for study specifically because of its similarity to the investigator's name, this mutant shows various and diverse conidial morphologies.

mo-2;morphological-2. This mutant also shows abnormal conidial morphology.

pi;pile. This mutant exhibits both abnormal mycelial and conidial growth. Minor constriction chains are plentiful, and major constriction chains can be observed occasionally.

rg-1;ragged-1. The mutant makes a weak attempt at macroconidiation but produces only stumps.

sc;scumbo. Aerial growth gives rise to structures faintly reminiscent of conidiophores but budding is defective, leading to a short lawn of stunted, branched hyphae.

sk;skin. This mutant grows very slowly and does not produce aerial hyphae. In some rare events, aerial hyphae can form and give rise to limited buds as shown in the picture.

sp;sponge. Slow mycelial growth leads to limited aerial growth. The overall growth pattern is reminiscent of a sponge (picture a; low magnification). Minor constriction chains and some major constriction chains can be observed (picture b; high magnification).

tng;tangerine. Growth is relatively normal; most proconidia are normal but a few appear to have entered uncontrolled growth. These proconidia far outgrow their neighbors on the proconidial chain (picture a) and ultimately grow to be several times their usual size (picture b). The growing conidia posess a membrane but no cell wall, and can engulf neighboring conidia as they grow, but are very fragile and tend to collapse spontaneously.

fl;dn;fluffy; dingy. This double mutant produces no macroconidia but copious amounts of microconidia (pictures a). As is the case with wild-type microconidia, the spores emerge from within hyphal cells by rupturing through the cell wall in an unconnected series (picture b). In some rare cases, a reversion to hyphal growth can be observed as a microconidium is followed by a thin hypha from the rupture (picture c).

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5/19/04 KMC