Germination physiology of Neurospora crassa conidia

Dormant conidia of Neurospora crassa for use in physiological studies were harvested from the parent mycelium with an isoparaffinic hydrocarbon fluid as a suspending medium. The effects of this hydrocarbon fluid and of water upon ungerminated spores were compared by measurements of polyribosome content, spore viability, changes in lipid content during storage of ungerminated spores, and germ tube emergence rates. These studies showed that the hydrocarbon fluid is an effective medium for harvest of the hydrophobic conidia because the hydrocarbon (unlike water) did not activate spore metabolism. The polyribosome analyses also confirmed the presence of preserved messenger RNA in the form of polyribosomes in the dormant conidia of N. crassa. Hydrocarbon harvesting of spores provided the opportunity to measure the rates of germ tube emergence, respiration, and RNA and protein synthesis without the influence of prior activation of the spores by water and to examine the role of water and the carbon source in the initiation of these activities. Rates of RNA synthesis lagged behind initial rates of protein synthesis, suggesting that early protein synthesis was being programmed by preserved mRNA. A metabolizable carbon source was found to have an important role in the general activation of germination in N. crassa conidia; in the absence of all nutrients except sucrose, the spores attained rates of protein synthesis comparable to those of spores incubated in a complete medium, and these spores exhibited low-to-moderate rates of germination, respiration, and RNA synthesis. Incubation of the spores in distilled water stimulated only additional polyribosome assembly and protein synthesis.