Phenolic variations in mite infected leaves of Quercus ilex L. (Fagaceae)

It has been suggested that non-glandular leaf hairs may have a significant role in plant defense against phytophagus enemies [1]. However, plant-mite interactions in Mediterranean ecosystems have not hitherto sufficiently studied in terms of chemical ecology. Quercus ilex is an excellent model for this type of study, as its leaves present impressive alterations (formation of red erineum) after Aceria ilicis (Eriophyoideae) attacks. In this study, isolated non-glandular leaf hairs from both healthy and mite infected leaves (1g) were extracted with solvents of increasing polarity. Methanol extracts were chosen for further HPLC/DAD/MS analyses, as they strongly differed in colour and weight. HPLC/DAD/MS analyses showed impressive changes in the polyphenolic profile of the infected areas: acylated flavonoid glycosides, mainly tiliroside and kaempferol-3-O-(2'',6''-di-E-p-coumaroyl)-glucoside, showed a 3 to 4 times decrease in the infected leaves, while water soluble secondary metabolites such as quercetin-3-O-glucoside, catechin and proanthocyanidin B3 showed a 3-fold increase. These results are well in accordance with the observed, under the microscope, morphological alterations, in particular the accumulation of red pigments in the hair and cells of the abaxial epidermis. They could be explained as the response of the plant against mite attack and underline the contribution of catechins and proanthocyanidins as antifungal and antifeedant agents to induced defence responses of plant tissues.

Aknowledgements: This project is co-financed within Op. Education by the ESF (European Social Fund) and National Resources.

References: 1. Levin, D. A. (1973) Quart. Rev. Biol. 43: 3.