Be aware when heat shocking ascospores from crisp mutants of Neurospora crassa.
Heather Cathcart, Sara N. Bennett, and Wayne A. Krissinger
Georgia Southern University, Statesboro, GA, P.O. Box 8042 30460
Fungal Genet. Newsl. 49:17
This laboratory has been working with a new crisp mutant of Neurospora crassa, crisp-5 isolated in our
laboratory by Charlene Jackson (Jackson, 1992 MS Thesis: 1-123) by ultraviolet irradiation. It is known that the
conidia of another crisp mutant, crisp-1, have constitutive thermotolerance (Cruz et al., 1988 Curr. Genet. 13,451-454). Based on this information, we tested the conidia of crisp-5 were tested for thermotolerance. This experiment
was designed to determine if the heat shock temperature and time, 60 °C for 30 minutes, used to induce germination
of ascospores, was sufficient to prevent germination of conidia with subsequent vegetative growth. To mimic the
heat shocking conditions encountered when isolating ascospores, a moistened swab was put into slant cultures of
crisp-5 and wild type (74-OR23-1A) and conidia were spread onto a 4% (w/v) agar slab. Small squares were cut out
of the middle of the slab and placed in 10x 75mm culture tubes containing 1ml each of the crossing medium of
Westergaard and Mitchell (1947 Am. J. Bot. 34:573-577), then heat shocked in a water bath for 30 minutes at 60°C.
The cultures were then incubated for up to 19 days at ambient temperature. Hyphal growth was observed in all tubes
with crisp-5 but in none of the tubes with wild type. When performing crosses with new mutant strains, it is
advisable to test the heat shock effect before heat shocking ascospores since vegetative growth not killed during the
heat shocking period might cause skewed results when scoring crosses.
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