Cloning of Phenylalanine Ammonia-lyase and its Role in Enzymatic Browning of Mung Bean Sprout during Cold Storage

Abstract

Mung bean sprout turns brown during cold storage. Here we cloned phenylalanine ammonia-lyase (PAL) mRNA and examined its expression during cold storage. A PAL cDNA of mung bean encoding 715 amino acids was cloned, which showed high homology to PAL genes of Fabaceae plants and had a highly conserved PAL motif including the active site (Ala-Ser-Gly). The expression of PAL mRNA increased during cold storage of mung bean sprout. The increase in expression was inhibited by the heat-shock treatment of mung bean sprout before storage. trans-Coumaroyltartronic and trans-caffeoyltartronic acids, the major substrates of polyphenol oxidase in mung bean sprout increased during cold storage. These results show that the PAL expression and biosynthesis of phenolics are essential for enzymatic browning of mung bean sprout during cold storage.