Claude Andary

Extraction and quantification of "condensed tannins" as a measure of plant anti-herbivore defence? Revisiting an old problem

Abstract. Contents of phenolic compounds in leaf extracts often serve as a measure of plant anti-herbivore defence. This method suffers from the multifunctionality of phenolics and from problems with their colorimetric quantification. Here we present further evidence for the pertinence of these problems. Contents of condensed tannins (CCT) were spectrophotometrically quantified in leaf extracts of 11 closely related mimosoid species, and Spodoptera littoralis caterpillars were reared on artificial diet containing these extracts. The relationship of CCT with caterpillar growth differed considerably among plant species, since both positive and negative correlations were detected. There was, however, a negative correlation of CCT with fungal spore germination, indicating a role of these compounds in resistance to fungi. Detailed knowledge on the structure and biological function of defensive compounds and on the overall composition of leaves is required to estimate a plants defensive efficacy against a particular group of enemies.

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.

Pectinase and hydrogen peroxide have differential effects on phenyl propanoid metabolism in Thunbergia alata

Abstract This report describes a study on the effects of pectinase and hydrogen peroxide (H2O2) on previously identified phenolic compounds in the leaves of Thunbergia alata. The elicitors were found to produce lesions resulting in the loss of chlorophyll and death of the cells surrounding the point of elicitation. At the optimal concentrations, hydrogen peroxide (15%) produces, after 24 hours, lesions that are 4 to 5 times greater than the lesions produced by pectinase (20 units/ml). Pectinase stimulates both local and systemic accumulation of the most pre-existing phenolic compounds, whereas hydrogen peroxide has no or little effect on the accumulation of some of these substances. Pectinase and in a less degree, hydrogen peroxide lead to the appearance of a new phenolic compound that is not present in control plants.