Extrafloral nectar secretion from wounds of Solanum dulcamara

Abstract

Plants usually close wounds rapidly to prevent infections and the loss of valuable resources such as assimilates(1). However, herbivore-inflicted wounds on the bittersweet nightshade Solanum dulcamara appear not to close completely and produce sugary wound secretions visible as droplets. Many plants across the plant kingdom secrete sugary nectar from extrafloral nectaries(2) to attract natural enemies of herbivores for indirect defence(3,4). As ants forage on wound edges of S. dulcamara in the field, we hypothesized that wound secretions are a form of extrafloral nectar (EFN). We show that, unlike EFN from known nectaries, wound secretions are neither associated with any specific structure nor restricted to certain locations. However, similar to EFN, they are jasmonate-inducible and the plant controls their chemical composition. Wound secretions are attractive for ants, and application of wound secretion mimics increases ant attraction and reduces herbivory on S. dulcamara plants in a natural population. In greenhouse experiments, we reveal that ants can defend S. dulcamara from two of its native herbivores, slugs and flea beetle larvae. Since nectar is defined by its ecological function as a sugary secretion involved in interactions with animals(5), such 'plant bleeding' could be a primitive mode of nectar secretion exemplifying an evolutionary origin of structured extrafloral nectaries.

Solanum dulcamara's response to eggs of an insect herbivore comprises ovicidal hydrogen peroxide production

“…Spodoptera exigua HÜBNER (Noctuidae) larvae were reared in vented plastic boxes (14 × 21 × 5 cm) on a bean flour-based artificial diet (Lortzing et al 2016). Boxes were kept in a climate chamber (24°C, 70% r.h., 16/8 h light/dark with 50% dimming for 1 h).…”

Transcriptomic responses of Solanum dulcamara to natural and simulated herbivory

“…It mostly occurs in wet habitats where it forms adventitious roots in response flooding (Dawood et al., , ). It hosts the economically relevant pathogen Phytophtora infestans (Golas et al., , ), a variety of different generalist and specialist herbivores (Calf & Van Dam, ; Viswanathan, Narwani, & Thaler, ), expresses inducible defence responses to herbivory such as the production of protease inhibitors (PIs; Nguyen et al., ; Viswanathan, Lifchits, & Thaler, ) and releases extrafloral nectar from herbivore‐inflicted wounds (Lortzing et al., ). Studying wild model plants and their natural interactions with herbivores potentially allows to identify and to functionally explore successful traits that plants evolved to cope with herbivores.…”

“…Studying wild model plants and their natural interactions with herbivores potentially allows to identify and to functionally explore successful traits that plants evolved to cope with herbivores. As S. dulcamara is predominantly attacked by specialists (Lortzing et al., ), it likely evolved effective defences against generalist herbivores and therefore we aimed to investigate the plant's response to a generalist. Native to Asia and now spread worldwide, the geographic range of the noctuid generalist S. exigua is overlapping with the native and invasive distribution of S. dulcamara .…”

Induced plant defences in biological control of arthropod pests: a double‐edged sword

“…Some of this food could be plant‐produced, such as extrafloral nectar. Its production is often inducible and even plants without nectaries can produce inducible nectar for effective indirect defence under field conditions . Natural enemy facilitation may also be achieved by plant breeding for traits that accommodate natural enemies such as low densities of trichomes, increased densities of domatia and increasing plant‐produced alternative food.…”