Effect of temperature and temperature shifts on growth and branching of a wild type and a temperature sensitive colonial mutant (Cot 1) of Neurospora crassa.

Growth of a temperature sensitive colonial mutant (cot 1) of Neurospora crassa was compared with a wild type strain. The hyphal growth unit (the ratio between mycelial length and number of branches) of the wild type was not appreciably altered by temperature and there was a direct relationship between the specific growth rate (alpha) of these mycelia and their mean hyphal extension rate (E). The specific growth rate of cot 1 increased by about the same relative amount as the wild type between 15 degrees and 30 degrees C. Cot 1 grew and branched normally at 15 degrees and 25 degrees C but at 30 degrees C the hyphal growth unit and mean hyphal extension rate of the mutant mycelia were reduced. Thus, between 15-30 degrees C the ratio, E/alpha was constant for the wild type but not for cot 1. The effect of temperature and temperature shifts on extension zone length (2), extension zone expansion time (2t) and branching of leading hyphae of mature colonies were also studied. It is suggested that branching is governed by a mechanism which regulates the linear growth rate of hyphae; the cot 1 mutation may have a direct effect on wall extension or affect linear growth rate indirectly due to an influence on the transport of precursors to the tip.