Biochemical studies of the germinating conidia of aspergillus nidulans

Abstract

Biochemical investigations of the germinating conidia of Aspergillus nidulans were carried out to elucidate the mechanisms controlling macromolecular synthesis during germ-tube emergence. Conidial germination of the wild type strain of A. nidulans, BWB 272, is accompanied by a hundredfold increase in a putrescine-stimulated S-adenosylmethionine decarboxylase activity and a rapid accumulation of spermidine and spermine. Putrescine levels remain low at all stages of growth. The highest specific rates of protein and nucleic acid synthesis occur coincident with germ-tube emergence. Use of metabolic inhibitors demonstrates the necessity of RNA and protein synthesis, but not DNA synthesis, for conidial germination. Comdia of the putrescine auxotroph, A. nidulans puA1, require putrescine for optimal rates of germination and growth. Putrescine starvation is a slow process resulting in a graoual run-down of a wide variety of metabolic processes. However a rapid change in the intracellular levels of spermidine and spermine occurs following the addition of putrescine to cultures starved for 12 hours. This results in immediate increases in the rates of protein and nucleic acid biosynthesis, oxygen consumption and polypeptide chain elongation. Also the average size of the isolated polysomes is three-fold larger and the proportion of ribosomal RNA synthesized increases two-fold. It is concluded that putrescine, spermidine and spermine are likely to have essential roles in macromolecular synthesis.