Phenylalanine ammonia‐lyase activity and capsaicin‐precursor compounds in p‐fluorophenylalanine‐resistant and ‐sensitive variant cells of chili pepper (Capsicum annuum)

Abstract

Cell suspension cultures of chili pepper (Capsicum annuum L. cv. Tampiqueño 74) displaying differences in their resistance to p‐fluorophenylalanine (PFP) and in their contents of capsaicin (the compound which is responsible for the hot taste of chili pepper fruits) were characterized in relation to the activity of phenylalanine ammonia‐lyase (PAL; EC 4.3.1.5), the levels of free l‐phenylalanine, phenolics and the phenylpropanoid acids involved in capsaicin biosynthesis. A nonselected cell line, a sensitive line (CA‐02), a moderately resistant cell line (CA‐29) and two resistant cell lines (CA‐04 and CA‐16) were studied. Higher PAL activities and higher levels of phenylalanine and phenolics were found in the PFP‐resistant cells even after a minimum of 9 subcultures (15 days each) in the absence of the analog, indicating that the selected trait was stable. PFP‐resistant chili pepper cells accumulated higher amounts of capsaicin precursors (cinnamic, caffeic and ferulic acids) than either the nonselected cells or the sensitive cell line. p‐Coumaric acid was not detected at significant levels in any of the cell cultures. Overall, accumulation of free phenyl‐alanine correlated well with PAL activity, phenolics, phenylpropanoids and capsaicin levels, suggesting an active flow through the phenylpropanoid pathway in PFP‐resistant cells of chili pepper.