The ultrastructure of dormant,germinating, and photo-inhibited uredospores of the rust fungusPuccinia graminis f. sp.tritici

Summary A comparison was made of fixed and non-fixed uredospores of the wheat stem rust fungusPuccinia graminis f. sp.tritici, using thin sectioning and freeze-etching. The latter technique yielded new information on the ultrastructure of dormant, germinating, and photo-inhibited uredospores, although the distribution of intramembranous particles (IMPs) was similar in each case. A stereological analysis of thin sectioned specimens provided quantitative data on organelle volumetric densities complementing the qualitative information. Evidence suggests that light acts by preventing the dissolution of wall material in the germ pore regions. Methylcis-ferulate, the uredospore self-inhibitor, is also believed to act at this stage in the germination process, and possible links between photo-inhibition and self-inhibition are discussed.