Cell Walls of Germinating Uredospores

Abstract

Synthesis of germ tube wall is a major quantitative event during germination penetration of fungi on host plants, but little is known of germ tube composition or metabolic regulation. Sonic oscillation was used to separate germ tubes from germinating uredospores of Uromyces phaseoli var. typica. Uniformly (14)C-labeled wall fractions from both structures were prepared by repeated low speed centrifugation and extraction with polar and nonpolar solvents. Based on amino acid analysis, approximately 6 and 16% of the carbon from uredospore and germ tube walls, respectively, was present in amino acids readily accessible to protease. Covalent linkages between amino acid and carbohydrate of walls was indicated by analysis of fragments prepared by mild hydrolytic procedures and separated by column chromatography and paper electrophoresis. The existence of protein in wall structures may resolve some previous uncertainty about the occurrence of protein biosynthesis during germination of rust fungi. Glucose, mannose, and glucosamine were the only carbohydrate components identified in both germ tubes and uredospore walls but different percentages were observed (germ tubes 28: 16: 16; uredospore 6: 36: 6). In germ tubes, most of the glucosamine was present in linkages hydrolyzed only by strong acid treatment, suggesting chitin-like polymers. In uredospore walls, glucosamine appears to be associated with red uredospore pigment which has properties similar to those of a melanin. Approximately 20% of the carbon in walls could not be identified with known compounds, partially because of degradation during the analytical procedures.