Mitosis and cell division in some cereal rust fungi. II. The processes of mitosis and cytokinesis

Abstract

Before mitosis in intercellular Puccinia graminis f. sp. avenae, P. coronata f. sp. avenue, and axenic P. graminis f. sp. tritici and P. coronata, the nuclei were reduced in size by nucleolar extrusion and (or) partitioning of variable portions of the nucleus. Also there was increased vesiculation in the cytoplasm with a corresponding increase in lipid and carbohydrate storage material.The mitotic spindle first formed in one corner of the nucleus, then elongated until the spindle poles were oriented at either end of the nucleus. During the intermediate stages of mitosis the chromatin was arranged around the periphery of the spindle, which consisted mostly of chromosomal fibres. In the later stages the nucleus elongated and became dumbbell-shaped, with long straight fibres passing through the nucleus from pole to pole. The end of mitosis was marked by the chromatin assuming a ‘two-track’ configuration at the poles on either side of the intranuclear fibres and by the breakdown of the nuclear envelope in the constricted region of the dumbbell-shaped nucleus.After the daughter nuclei had separated, they migrated into new hyphal branches and septum synthesis was subsequently initiated. The septa grew by centripetal invagination in both the intercellular and the axenic hyphal states. There were often accumulations of mitochondria in the region of septal growth. Mature septa of intercellular P. coronata and axenic P. coronata and P. graminis tritici were typical of those found elsewhere in the rust fungi.