Ultrastructural studies of cold-dormant and germinating uredospores of Puccinia graminis var. tritici

Abstract

Uredospores of Puccinia graminis var. tritici that have been subjected to temperatures below freezing are shown not to differ ultrastructurally from fresh uredospores, although a need for a heat-shock has been induced. Moreover, no ultrastructural differences have been observed between germinating uredospores of both types. Germination results in the formation of large numbers of vesicles and in the change in shape of mitochondria from ellipsoidal and spherical to elongate. A unique aspect of germinating uredospores is found in permanganate-fixed cells wherein electron-transparent patches appear, giving the cytoplasm a "foamy" appearance. The consequences of the suspension of cold-dormant uredospores in liquid medium without a prior heat-shock include irreversible failure to germinate and severe disruption of lipid inclusions and other cytoplasmic elements.