Gene structure and expression of cinnamic acid 4-hydroxylase in potato and its relationship to after-cooking darkening

After-cooking darkening (ACD) is a gray-black discoloration of the potato tuber, formed after cooking by the oxidation of an iron-chlorogenic acid complex. Cinnamic acid 4-hydroxylase (C4H) is a key enzyme involved in the biosynthesis of chlorogenic acid. In this study, the full-length c4h gene was cloned and sequenced from both genomic DNA and cDNA of Russet Burbank tuber tissue by PCR and 5' and 3' RACE. The gene expression levels of c4h were examined by Northern hybridization in potato cultivars varying in susceptibility to ACD. Results suggest that there is a relationship between the levels of c4h gene expression and the degree of ACD in potato tubers. A preliminary investigation on the chemical inhibition of the C4H enzyme in potato plants revealed that nutrient-deficient plants produced approximately 8-fold more chlorogenic acid than healthy plants. The inhibition of C4H in nutrient-deficient plants resulted in slightly decreased chlorogenic acid production.