Herbivory, induced resistance, and interplant signal transfer in Alnus glutinosa

T. Tscharntke et al., Herbivory, induced resistance, and interplant signal transfer in Alnus glutinosa, BIOCH SYST, 29(10), 2001, pp. 1025-1047
Citations number
Categorie Soggetti
Journal title
ISSN journal
0305-1978 → ACNP
Year of publication
1025 - 1047
SICI code
Field experiments with manually defoliated black alders (Alnus glutinosa) s howed that defoliation affected herbivory by the major alder antagonist, th e leaf beetle Agelastica alni. Herbivore damage increased with increasing d istance to the defoliated tree, suggesting induced resistance not only on t he damaged tree, but also on the neighbouring trees. The beetles also avoid ed leaves from the nearest neighbours for both feeding and oviposition in a laboratory assay, so the alders showed interplant resistance transfer. Nat ural enemies did not appear to shape this pattern., because the number of e ntomophagous arthropods and predator-prey ratios even increased with increa sing distance to the defoliated tree. The numbers of all specialist, but no t the generalist, herbivore species paralleled the increase in the attack o f the specialist A. alni, supporting the view that specialists are more aff ected by plant resistance than generalists. Mechanisms causing this pattern, found in the field, were studied in more d etail using biochemical analyses and further bioassays. Responses of alder leaves to herbivory of A. alni were shown to include ethylene emission and the release of a blend of volatiles with mono-, sesqui- and homoterpenes. C hanges in leaf chemistry after herbivory included increases in the activity of oxidative enzymes (polyphenoloxidase, PPO, lipoxygenase, LOX, and perox idase, POD) and proteinase inhibitors (Pis). and an increase in the phenoli c contents of the leaves. Quantification of the endogenous jasmonic acid (J A) showed the activation of the octadecanoid pathway following herbivory. The active components in mediating a possible interplant signal transfer vi a airborne volatiles may have included ethylene, beta -ocimene. 4,8-dimethy lnona-1,3,7-triene (DMNT), and 4,8,12-trimethyltrideca-1.3,7,11-tetraene (T MTT). The incubation with volatiles resulted in an increase in the activity of catalase (CAT) and Pis (after MeJA application) and in an increase in t he content of phenolics and PI activity (after ethylene application). Furth er evidence that airborne interplant communication may be important in the response of alder trees to beetle attack came from container experiments, I n airtight chambers, unattacked leaves significantly increased the activity of proteinase inhibitors when they were associated with leaves previously attacked by beetle larvae. In conclusion, field experiments, bioassays in the laboratory as well as bi ochemical analyses suggest the existence of interplant resistance transfer in A. glutinosa. with airborne volatiles as a possible mechanism. However. the relative importance of airborne and possible soil-borne signals as well as unknown effects of intensified nutrient absorption of defoliated trees. possibly reducing foliage quality of undamaged neighbours, remains to be s hown. (C) 2001 Elsevier Science Ltd. All rights reserved.