Compartmentation of metabolic systems in the regulation of dormancy in fungus spores

Abstract

Dormancy in fungus spores can be due to a variety of causes relating to structural, physiological, or biochemical functions. Based on data reported here and earlier, compartmentation of endogenous reserves or of enzymes is proposed as the mechanism controlling dormancy in spores of Myrothecium verrucaria and Trichoderma reesei. Spores of both organisms contain a pool(s) of reserves composed of trehalose, amino acids, as well as unidentified compounds. Addition of hot water extracts of these reserves to spores results in rapid increases in respiratory activity and germination. This observation coupled with other data showing the stimulation of endogenous respiration by heat, freezing, or azide demonstrates that dormancy is due primarily, if not entirely, to sequestering or compartmentation of the endogenous reserves and not of the enzymatic systems involved in utilization of metabolites for germination. Presumably these reserves are contained within the vacuoles. Data on the interactions of treatments that stimulate endogenous respiration and on the effects of metabolism of exogenous substrates indicate that the transport pathways within the cell, from the pools or from the plasma membrane, to the loci of initial metabolism are not identical and that the total regulatory system is composed of a number of separable processes. It appears probable that examination of the spores of other fungi will show that compartmentation of reserves is not of uncommon occurrence and is not an unusual cause of dormancy.