UC Davis

Phenylalanine ammonia-lyase (PAL) catalyses the first step controlling the rate of phenylpropanoid metabolism. Wounding is a ubiquitous stress in nature and in the harvesting and preparation of fruits and vegetables that induces an increase in PAL activity, an accumulation of phenolic compounds and subsequent tissue browning. A wound-inducible PAL gene (LsPAL1) was isolated from Romaine lettuce by RT-PCR. The putative protein encoded by LsPAL1 is similar to predictive polypeptides sequences for other PALs. The kinetics of PAL mRNA accumulation is similar to those of induced PAL enzyme activity, with enzyme activity following mRNA accumulation by 12 h. Wound-induced PAL transcripts accumulated in cells close to the wound sites. Tissue printing showed that PAL mRNA was associated with tissue next to the epidermis and vascular bundles. A heterologous PAL protein was expressed in E. coli and was found to show significant PAL activity.