Structures on the surfaces of leaves, such as dense layers of
non-glandular trichomes, strongly affect phylloplane mite activities. On
the other hand the feeding of eriophyoid mites on leaf surfaces can
cause hyperplasia of leaf trichomes (erinea formation). In many cases
the hyperplasia is accompanied by the accumulation of pigments within
trichome cells, causing an impressive red-brown colouration of the
erineum. There is no information, however, on the structure of these
pigments as well as on the chemical alterations in the phenolic content
of plant trichomes in response to mite attack. Erinea formation on the
abaxial surface of Quercus ilex leaves upon Aceria ilicis (Acari:
Eriophyoidea) attack provides an excellent model on this topic.
Differences in the structure and chemical composition of isolated
trichomes derived either from healthy (normal trichomes) or mite
attacked (hypertrophic trichomes) leaves were examined. Carbon
investment was comparable between the two different trichome types, but
the cell walls of the hypertrophic trichomes appeared thinner and did
not contain microcrystalline cellulose. Observations under the
fluorescence microscope showed that the emitted fluorescence was
different between the two trichome types, indicating a different
composition in fluorescencing phenolic compounds. The chemical analyses
confirmed that hypertrophic trichomes contained higher concentrations of
the feeding deterrents proanthocyanidin B3 and catechin, as well as of
quercetin-3-O-glucoside, but lower concentrations of acylated flavonoid
glycosides, than the normal ones. The results showed that the structural
and functional changes in leaf trichomes upon mite attack may be an
effort of the leaf to compensate the damage caused by the pest. (C) 2010
Elsevier Ltd. All rights reserved