Wall structure and ornamentation of the urediniospores of Uromyces viciae-fabae

Abstract

The development of the spines and the structure and composition of the urediniospore wall of Uromyces viciae-fabae have been studied by low-temperature scanning electron microscopy, cytochemical localization, chemical, and enzymic digestion techniques. Spine formation was similar to that previously described for urediniospores of other rust fungi. Swollen collars that are distinct from the annular ridges are only evident in frozen-hydrated spores and surround the bases of spines. Pockets of endoplasmic reticulum line the periphery of spores and mark the sites of spine development. This endoplasmic reticulum may have a role in the production of enzymes and (or) structural proteins or glycoproteins. Microfibrils are present in digested and shadowed wall preparations, often associated with spines. Enzymic digestion treatment suggests that these microfibrils are chitin. Around the bases of the spines, microfibrils are orientated circumferentially and contribute in part to the thickened, annular ridges evident in all spore preparations. The spore wall matrix consists of polysaccharides. Colloidal iron staining indicates acid mucopolysaccharides. Differences in reaction of the urediniospore wall to colloidal iron at what appears to be the same stage of development suggests in situ chemical change(s), which may in turn be linked with changes in wall plasticity.