Effects of wounding and salicylic acid on hydroxycinnamoylmalic acids in Thunbergia alata

We describe the identification of three phenolic compounds (caffeoylmalic, feruloylmalic and p-coumaroylmalic acids) in the leaves of Thunbergia alata. Caffeoylmalic and feruloylmalic acids represent the majority of all the derivatives of hydroxycinnamic acid in this plant. Elicitation with 5 mM of salicylic acid (SA) after wounding produces an intense necrotic reaction which reaches a peak after 24 h. This reaction is much less intense when the leaves are subjected to wounding alone. HPLC analysis of the above three acids in leaf samples taken 24 h after treatment shows that the concentration of caffeoylmalic acid increases in the case of both wounding and SA treatment. The level of feruloylmalic acid increases principally in response to wounding while the concentration of p-coumaroylmalic acid increases essentially following elicitation by SA. The accumulation of these three compounds occurs not only in directly treated leaves, but also in untreated leaves situated above treated leaves (systemic accumulation). Wounding and SA produce a greater local accumulation of feruloyl and p-coumaroylmalic malic acid, respectively. For caffeoylmalic acid, wounding produces the greatest local accumulation whereas in response to SA, systemic accumulation of this compound is greater. Plants aged 2 months are more sensitive than younger plants to these two stress treatments.