Changes in activity of lysosomal ribonuclease following mechanical damage to leaves of Solanum tuberosum L.

Differential centrifugation experiments showed that the 13-fold increase in total acid ribonuclease (RNase) activity arising during the 48 h following mechanical damage to potato leaves was associated, in about equal proportions, with the sedimentable and supernatant fluid fractions of cell homogenates. Density gradient ultracentrifugation techniques revealed that the majority of the particulate activity of RNase was located in the lysosomal fraction of leaf homogenates. Although [(14)C]leucine was incorporated into leaf lysosomes during incubation following mechanical damage the various molecular forms of RNase purified from the organelles, one of which had a specific lysosomal location, contained negligible radioisotope. That form of the enzyme which did incorporate [(14)C]leucine was one of those confined to the supernatant fluid fraction of leaves.In addition to the massive quantitative changes in RNase activity which occurred subsequent to mechanical damage, extensive qualitative changes occurred in the complement of molecular forms of lysosomal RNase. The possible origins of these changes are discussed.