[An analysis of the quantitative importance of some metabolic pathways in uredopores of Puccinia graminis var. tritici].

In order to investigate the metabolism of germinating uredopores of Puccinia graminis, spores were incubated at different stages of germination with (14)C-valerate-1 for short times (5 or 10 min). Incorporation of the labelled substance per unit of time was nearly constant during the experiment, which lasted for 510 min. The uptake of valeric acid was not influenced by endogenous metabolism. Most of the incorporated radioactivity was soluble in 40% ethanol and water. The part of the activity taken up that was incorporated into insoluble compounds decreased during germination. Distribution of radioactivity in some important metabolites such as glutamic acid, aspartic acid, citric acid, malic acid, carbohydrates and alanine was determined in terms of the per cent of incorporated radioactivity. Radioactivity of these compounds accounted for 70% of the radioactivity of the raw extract. Most of the radioactivity of the raw extract was found in glutamic acid and glutamine.The endogenous supply of acetyl CoA decreased gradually, and thereby turnover rates of citric acid and glutamic acid decreased, too. The specific activity of acetyl CoA (formed by β-oxidation of valeric acid) increased since the rate of supply of radioactive acetyl CoA was constant. Thereby the specific activities of the different pools increased, as long as pool sizes were constant.Pool sizes did not change during tracer application, indicating steady state conditions during the experiments. During germination the citric acid pool and the aspartic acid pool stayed practically constant. The glutamic acid pool decreased and the malic acid pool increased. Turnover rates of glutamic acid including glutamine and aspartic acid including asparagine were very high.Quantitatively the TCA cycle is more important than the glyoxalate cycle. During germination synthesis of glutamic acid decreased and synthesis of carbohydrates and aspartic acid increased, indicating that more iso-citrate was split by isocitratlyase.Large differences in the rates of synthesis of different amino acids were noticed. Only glutamic acid, aspartic acid and alanine were synthesized in larger amounts. On the other hand the amount of synthesis of serine and threonine was extremely low and insufficient for a net synthesis of proteins. The rate of protein synthesis was investigated by studying incorporation of free glutamic acid into bound glutamic acid. Only a very small part of the synthesized free glutamic acid was bound. The rate of protein synthesis decreased during germination.