Changes in two ribonuclease isozymes during rust infection of flax cotyledons.

A ribonuclease fraction previously purified from flax by gel filtration was further resolved into two components by hydroxyl apatite chromatography. These were homogeneous with respect to electrophoresis and isoelectric focusing. Both enzymes are of RNase I type but differ in substrate specificity, kinetic properties, pH response, and isoelectric point.The two RNase isozymes show consistent properties when extracted from variety Bison (susceptible) or variety Bombay (resistant) with or without infection with race 3 of flax rust. The relative amounts of these isozymes change markedly during infection. These observations provide an explanation for the apparent qualitative changes in RNase noted previously. Differences between susceptible and resistant reactions in the early stages of disease are discussed.