Ellagitannins: defences of Betula nana against Epirrita autumnata folivory?

摘要

The induced resistance of the subarctic mountain birch Betula pubescens ssp. czerepanovii is a well-characterized phenomenon, whereas the induced responses of Betula nana L., one of the parental species of mountain birch, have not yet been characterized. Betula nana is more resistant to several classes of insectivorous herbivores than the mountain birch, although the mechanisms responsible for the better ability to resist herbivores are not known. The present study aimed to determine the metabolic changes that are induced by early season herbivory in B. nana leaves and to study the effects of rapidly induced resistance on the growth of Epirrita autumnata larvae. Defoliation of B. nana was accomplished by E. autumnata larvae and leaf samples for chemical analyses were collected when the defoliating larvae were at their third and fifth instar. At the same time, laboratory assays for the growth and consumption rates of E. autumnata larvae were conducted. The wounding of leaves by E. autumna larvae induced the production of ellagitannins (ETs) in B. nana. Intriguingly, the concentrations of protein-bound amino acids were also induced by herbivory; however, an increase in proteins was not mirrored in the growth rate of larvae, which was less on the induced foliage. The decreased growth rate of larvae was apparently linked to the increased concentrations of oxidatively-active ETs and the high concentration of ETs may explain the better resistance of this parental species compared with the hybrid mountain birch with its lower levels of ETs.