Blackspot bruise dependent changes in enzyme activity and gene expression in Lemhi russet potato

Blackspot bruise-induced changes in enzyme activity and gene expression were examined in the bruise susceptible cultivar Lemhi. The activities of several enzymes involved with the synthesis and metabolism of phenolic intermediates were examined over the time course of blackspot bruise development in tubers. A large, transient increase (200-fold) in phenylalanine ammonia lyase (PAL) activity was observed, while other enzymes examined (chorismate mutase, tyrosine ammonia-lyase, 3-deoxy-D-arabino-heptulosonate 7-phosphate synthase, and polyphenol oxidase) showed either modest or no activation. Maximal PAL activity was observed 48 hours after bruise induction, well after the discoloration reactions were complete. The change in PAL activity was associated with a transient increase in messenger RNA coding for PAL. In addition, messenger RNAs encoding two stress-induced genes, ubiquitin and the 70 kD heat shock protein, were transiendy induced by bruising. Physical impact also induced a marked decrease, followed by recovery, in the messenger RNA level for patatin, a primary storage protein in the tuber. These results suggest that the stress resulting in blackspot bruising elicits a wound response similar to those observed in other injuries to plant tissues.