Immunological Memory of Mountain Birches: Effects of Phenolics on Performance of the Autumnal Moth Depend on Herbivory History of Trees

Abstract

Plants have been suggested to have an immunological memory comparable to animals. The evidence for this, however, is scarce. In our study with the mountain birchEpirrita autumnata system, we demonstrated that birches exposed as long as 5 yr to feeding of E. autumnata larvae (delayed induced resistance, DIR), responded more strongly to a new challenge than trees without an herbivory history. Pupal weights remained lower, and the duration of the larval period was prolonged in the DIR trees, although immunity, measured as an encapsulation rate, was not affected. We further demonstrated that the effects of birch phenolics on performance of E. autumnata were different in the exposed (DIR) trees from naive control trees, although we found only one significant change in chemistry. The quercetin:kaemferol ratio was increased in DIR trees, suggesting that herbivory caused oxidative stress in birches. In DIR trees, phenolics, especially hydrolyzable tannins (HTs), affected pupal weights negatively, whereas in control trees, the effects were either nonsignificant or positive. HTs also prolonged the duration of the larval period of females, whereas peroxidase (POD) activity prolonged that of males. We suggest that the causal explanation for the induced resistance was an enhanced oxidation of phenolic compounds from the DIR trees in the larval digestive tract. Phenolic oxidation produces semiquinones, quinones, free radicals, and ROS, which may have toxic, antinutritive, and/or repellent properties against herbivores.

Genetic and phenotypic relationships between immune defense, melanism and life-history traits at different temperatures and sexes in Tenebrio molitor

“…Studies in insects testing sexual dimorphism in immune defense have resulted in mixed findings (for example, CordobaAguilar et al, 2006, Rantala andRoff, 2007). It has been found that there is sex difference in response to genetic (Rantala and Roff, 2007) and nutritional stress (McKean and Nunney, 2005;Ruuhola et al, 2007) that may cause between population and species variation in sex difference in immunity. In the present case, encapsulation ability was highest in females and the gender difference showed a modest or no change with temperature.…”

Mountain birch – potentially large source of sesquiterpenes into high latitude atmosphere

“…Immunological memory of mountain birch after herbivory by autumnal moth is discussed by Ruuhola et al (2007). They found out that delayed induced resistance lasted as long as five years.…”

“…Mechanical damage of leaf tissue is known to induce an immediately enhanced production and emission of volatiles (Juuti et al, 1990). However, it has also been suggested that an immunological memory effect of herbivore attacks, potentially affecting the composition of the emitted VOC mixture, may persist for several years after the actual defoliation event (Ruuhola et al, 2007).…”

Genetic and Environmental Factors Behind Foliar Chemistry of the Mature Mountain Birch

“…However, several studies conducted on relationships between individual phenolic compounds and herbivory have given contrasting results Ruuhola et al, 2007). A plant's suitability for herbivores also has been connected to plant oxidases, such as polyphenoloxidases (PPOs) and peroxidases (PODs) (Felton et al, 1989;Appel, 1993).…”

“…Methods for extraction, analysis, and identification of phenolic compounds are described in Salminen et al (1999Salminen et al ( , 2001. Enzyme activities of the birch leaves were analyzed as in Ruuhola and Yang (2006) and Ruuhola et al (2007). Enzyme activities were measured in triplicate.…”