PAL inhibitor evokes different responses in two Hypericum species

Accumulation of secondary metabolites (general phenols, naphthodianthrones and phloroglucinol hyperforin) in Hypericum perforatum and Hypericum canariense after application of the inhibitor (2-aminoindane-2-phosphonic acid, AIP) of the pivotal enzyme of general phenylpropanoid pathway (phenylalanine ammonia-lyase, PAL) was studied. Shoots of H. perforatum revealed more expressive growth depression, concomitantly with the inhibition of PAL activity (−60%) and decrease in soluble phenols and individual phenolic acids in response to AIP. Hypericins (hypericin, pseudohypericin and protohypericin) decreased while hyperforin increased in AIP-cultured H. perforatum. On the contrary, growth changes, decreases in soluble phenols and individual phenolic acids were less-visible in H. canariense. This was also reflected in restoration of PAL activity (+330%) and selected flavonoids even increased. Hypericins and hyperforin were present in several orders of magnitude lower amounts in comparison with H. perforatum. Increase in proline indicates potential compensatory antioxidative mechanism if phenols are depleted. Microscopy revealed also differences in secondary xylem formation and lignification between species after exposure to AIP.

► Effect of PAL inhibitor (AIP) on Hypericum perforatum and Hypericum canariense was compared.
► Growth and PAL activity were suppressed more by AIP in H. perforatum.
► Soluble phenols and many phenolic acids were less affected by AIP in H. canariense.
► Lignin was more suppressed while some flavonoids increased by AIP in H. canariense.
► Hypericins decreased while hyperforin increased in AIP-cultured H. perforatum.