Decreased Phenylalanine Ammonia-Lyase and Ribonuclease Activity in Side Roots of Carrot Infested With the Northern Root-Knot Nematode

Abstract

Activity of phenylalanine ammonia-lyase (PAL) and ribonuclease was determined in side roots and storage root tissues of healthy and Meloidogyne hapla infested 4-month-old carrot plants cv. Perfekcja and cv. Slendero, that had been induced with phenylalanine for 24 h in the dark. Activity of both enzymes was lower by 50% or more in the galled side roots as compared to the healthy roots. In contrast, PAL activity was enhanced in the secondary phloem and secondary xylem of the storage root of the infested plants. It is suggested that decreased PAL activity in the galled roots may be associated with reduced lignin biosynthesis, thereby facilitating cell enlargement and cortical hypertrophy.