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Properties of Germination Inhibitors from Stem Rust Uredospores. Paul J. Allen, Professor, Department of Botany, University of Wisconsin, Madison 53706; Richard N. Strange(2), and Mohamed A. Elnaghy(3). (2)(3)Former Postdoctoral Research Associates, Department of Botany, University of Wisconsin, Madison 53706, Present address of junior authors: Department of Botany and Microbiology, University College, London, England; and Department of Botany, Assiut, Egypt. UAR. Phytopathology 61:1382-1389. Accepted for publication 28 June 1971. DOI: 10.1094/Phyto-61-1382.

Inhibitor can be extracted from wheat stem rust uredospores with water but not with dry organic solvents. A preliminary extraction of the spores with ether aids in purification. The inhibitor partitions from aqueous solutions into ether at a pH of 8.5 or below, but not at 12.5. It is more stable in ether than in aqueous solution, and inactivates rapidly at higher pH values. Purification was facilitated by partitioning a water extract into ether, evaporating the ether, and reextracting the residue with water. The most active preparations gave 95% inhibition at concentrations of 10-25 ng/ml. Chromatography on cellulose with aqueous solvents resolved the inhibitor into two components, with R_f values slightly lower than those of the two components of bean rust inhibitor. In most chromatographic systems, only one component appeared. Ultraviolet absorption by the inhibitor was indicated, but was not clearly defined because of evidence of impurities even in the most active preparation. Fluorescence at inciting wavelengths of 254 and 366 nm was either weak or lacking. Evidence suggests that the inhibitors are phenolic compounds which are interconvertible, and that they are closely related to, but not identical with, the inhibitors from bean rust uredospores.