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Physiology and Biochemistry

Changes in Barley Leaf Ribonucleases During Early Stages of Infection by Erysiphe graminis f. sp. hordei. Arun K. Chakravorty, Senior lecturer, Department of Biochemistry, University of Queensland, St. Lucia, Queensland 4067, Australia; K. J. Scott, professor, Department of Biochemistry, University of Queensland, St. Lucia, Queensland 4067, Australia. Phytopathology 69:369-371. Accepted for publication 10 October 1978. Copyright 1979 The American Phytopathological Society. DOI: 10.1094/Phyto-69-369.

Ribonuclease fractions from the barley powdery mildew fungus (Erysiphe graminis f. sp. hordei Marchal, race 3) and a susceptible cultivar of barley (Hordeum vulgare ‘Prior’) have been purified to a high specific activity by Sephadex G-100 gel filtration in the presence of 3.0 M urea. Upon gel filtration the enzymes (termed pH 5-insoluble RNases of molecular weights 24,000 and 10,000 respectively) from healthy and inoculated plants yield two distinct peaks of enzymatic activity. The corresponding enzyme fraction from the powdery mildew fungus yields a single peak of activity of molecular weight about 12,000 daltons. The major peak of RNase activity obtained from inoculated barley leaves 48 hr after inoculation is remarkably different from that obtained from the healthy leaves or from the fungus with respect to its substrate preference as judged by the relative rates of hydrolysis of synthetic ribohomopolymers. These results suggest a dramatic change in the catalytic properties of this RNase of barley leaves at an early stage of host-parasite interactions.