Some Characteristics of a Lipase Preparation from the Uredospores of Puccinia graminis tritici

The characteristics of a lipase preparation from the uredospores of Puccinia graminis (pers.) f. sp. tritici (Eriks. and Henn.) have been investigated. The majority of the lipolytic activity in disrupted uredospores was found to be associated with a lipid-containing, particulate fraction which sedimented at 5000g. With triolein as a substrate, both 1,3- and 1,2-diglycerides were formed. Ethylenediaminetetraacetate, p-chloromercuribenzoic acid, and Hg²⁺ strongly inhibited the activity. A pH optimum of 6.7 was observed. The sensitivity of the preparation to higher temperatures was indicated by a complete loss of activity when the preparation was preincubated at 25 C or above for 30 minutes. A temperature optimum of 15 C for the enzyme is strikingly similar to the temperature optimum for germination of the uredospores. The possible relationship between the sensitivity of the enzyme and the germination process is discussed.     

Carbohydrate Uptake and Metabolism of Ophiobolus graminis

The carbohydrate nutrition of Ophiobolus graminis, the cause of the take-all disease of wheat, was investigated in growth and respiration experiments. In a synthetic medium, d-mannitol was the only carbohydrate of thirteen studied which the fungus could not use for growth. However, the fungus was found to take up mannitol by an active mechanism, which was stopped by 2,4-dinitrophenol. Di- and trisaccharides were hydrolyzed extracellularly, and the monosaccharides were assimilated at different rates.     

The Nature of Cold-induced Dormancy in Urediospores of Puccinia graminis tritici

When air-dry urediospores of the wheat stem rust, Puccinia graminis f. sp. tritici, are exposed to temperatures below freezing, their germinability is markedly reduced, even after prolonged thawing at room temperature. Germinability is fully restored by a brief heat-shock or by vapor phase hydration. We have found that this “cold dormancy” cannot be reversed once the spores contact liquid water. Enhanced loss of metabolites occurs immediately upon suspension of cold-dormant urediospores in liquid without a prior heat-shock. Such leakage is two to three times greater than from untreated or heatshocked cold-dormant spores and accounts for up to 70% of the soluble pool of metabolites normally present in germinating urediospores. Respiratory activity of cold-dormant urediospores declines rapidly during incubation in liquid. Incorporation of isotopic carbon into cold-dormant urediospores is only a fraction of that of untreated or heat-activated spores. Thus, cold shock transforms the spores into a state of supersensitivity to liquid water, which is reversed by heat-shock or slow hydration by vapor phase equilibration. The primary cause of damage to cold-dormant cells exposed to liquid water appears to be irreversible permeability damage, followed by metabolic injury.     

Quantitative studies of the post-penetration phase of infection by Puccinia graminis tritici

Data obtained during the first 120 h after several resistant and susceptible varieties of wheat and some non-host species were inoculated with uredio-spores of Puccinia graminis tritici provided further evidence in support of the suggestion that hypersensitive necrosis is a consequence, and not the cause, of resistance. No evidence was obtained that individual genes for stem-rust resistance specifically influenced colony growth or the histological changes that occurred during infection. However, combinations of major resistance genes or the presence of minor genes for resistance apparently did affect colony growth and hypersensitive cell collapse. Three groups of varieties – resistant, intermediate and susceptible – were distinguished on the basis of colony growth and the amount and proportion of necrotic tissue associated with colony development. The boundary between the intermediate and susceptible groups was not as distinct as that between the intermediate and resistant groups.     

Wachstum und Sporenbildung einer schweizerischen Rasse von Puccinia graminis tritici in vitro

Growth and spore formation of a Swiss race of Puccinia graminis f. sp. tritici in vitro On a medium containing Evans Pepton and yeast Extract, the rust formed aecidiospores in great number. The aecidiospores were able to infect wheat plants. On media 4–9 (Table 1) uredospores and teliospores are formed. Highest numbers of teliospores were produced on substrates with ATP, nucleotide bases, and ribose.     

Transient transformation of the rust fungus Puccinia graminis f. sp. tritici

The biotrophic rust fungus Puccinia graminis f. sp. tritici (Pgt) was transformed by particle bombardment. The promoter from the Pgt translation elongation factor 1alpha (EF-1alpha) gene was fused to the bacterial marker genes hygromycin B phosphotransferase (hpt) and beta-glucuronidase (GUS). Transformation constructs were introduced into uredospores of Pgt, an obligate pathogen of wheat, by biolistic bombardment. Uredospores transformed with the construct containing the hpt gene germinated and initiated branching on selective medium, indicating that they had acquired resistance to hygromycin B. However, transformants stopped growing 5 days after bombardment. GUS activity in uredospores and germlings was histochemically detected 4-16 h after bombardment. GUS expression was also obtained using the INF24 promoter from the bean rust fungus Uromyces appendiculatus, demonstrating that heterologous genes can be expressed in P. graminis under the control of regulatory sequences from closely related organisms.     

Zum Stoffwechsel des Mycels von Puccinia graminis var. tritici auf der Weizenpflanze

Summary Rusted wheat leaves were incubated simultaneously with alanine-1-¹⁴C and glucose-6-T. Uredospores formed during the application of the tracers were collected and the bound alanine was isolated from the spores and the host tissue. Comparison of the ¹⁴C/T ratio of spore-alanine and host-alanine indicates that the mycelium not only withdraws alanine from the host but in addition carries out an alanine synthesis on its own. This alanine is synthesized from glucose which the mycelium takes up from the host.