Changes in the Ribonuclease Activity of Flax Cotyledons following Inoculation with Flax Rust

There was a significant increase in the ribonuclease activity of both resistant (Bombay) and susceptible (Bison) varieties of flax (Linum usitatissimum L.) 3 to 4 days after inoculation with flax rust (Melampsora lini [Pers.] Lev., race No. 3). A second and much greater increase in the activity of this enzyme occurred only in the susceptible host at later stages of disease development. While a similar increase in ribonuclease level was also caused by mechanical injury, evidence is presented showing qualitative differences between the enzyme from parasitized tissue and that from the mechanically injured cotyledons. Comparison of the enzyme from healthy and inoculated cotyledons and from flax rust revealed the presence of a relatively unstable component and some unique catalytic properties in the enzyme from inoculated cotyledons.