Ultrastructural changes in the conidia of Penicillium notatum during germination

Abstract

To study the changes in the cell wall of Penicillium notatum during germination, thin sections of resting, swollen, and germinating spores, and mycelium were compared with thin sections of the isolated cell walls. In the cell wall of resting spores four distinct layers were found. The outermost layer of the cell wall of resting spores was released during swelling and the two inner layers were extended to form the cell wall of the germ tube. The cell wall of young germ tubes had only two layers but a new electron-dense layer was formed later on the outside. Mycelial cell walls which appeared thinner than those of conidia showed three distinct layers. Large mitochondria that divide during germination were present in both resting and swollen spores. Two different types of vacuoles were found, both of which decreased in size and in number during germination. Endoplasmic reticulum was almost absent in resting spores but increased substantially during swelling.