Broad bean cultivars increase extrafloral nectary numbers, but not extrafloral nectar, in response to leaf damage

Phenotypic plasticity allows organisms to maximize fitness, by optimizing the expression of costly defensive traits. Broad bean, Vicia faba L. “Broad Windsor”, produces increased numbers of extrafloral nectaries (EFNs) in response to leaf damage to attract mutualistic partners and reduce herbivory. It is currently unknown, however, whether EFN induction is cultivar-specific or is a more general phenomenon. It has also not been determined whether broad beans increase nectar secretion rates in conjunction with EFN induction. We hypothesized that: a) as all broad beans have conspicuous EFNs, all cultivars should produce additional EFNs in response to leaf damage, and b) overall nectar secretion rates should increase with EFN numbers, to attract additional mutualists. We tested our hypothesis by subjecting three broad bean cultivars, Vicia faba L. “Broad Windsor”, “Stereo”, and “Witkiem” to mechanical leaf damage. The degree of change in plant traits associated with growth, in addition to EFN induction, was assessed 1 week after leaf damage. Extrafloral nectar volumes were also assessed, every 24 hours, pre- and post-leaf damage. We confirmed our first, but rejected our second, hypothesis. All cultivars produced additional EFNs, but none increased extrafloral nectar volumes, when experiencing leaf damage. Further experimentation is required to determine if energetic tradeoffs limit multiple forms of defense (i.e., EFN vs. nectar induction), or if this alternative strategy is adaptive for attracting and retaining mutualists. Understanding the costs and benefits of EFN vs. nectar induction will provide insight into the evolution of defensive mutualisms between plants and predatory arthropods.

Extrafloral nectary-the sleeping beauty of plant science

Cotton is one of the most important cash crops,its growth season coincides with a high incidence of diverse groups of pests,leading to heavy use of pesticides.Recent identification of a signaling protein as a candidate regulator of cotton extrafloral nectary provides a new insight into the formation of sophisticated defense mechanisms in plants.

Floral nectary, nectar production dynamics, and floral reproductive isolation among closely related species of Pedicularis

Floral nectar is thought to be one of the most important rewards that attract pollinators in Pedicularis; however, few studies have examined variation of nectary structure and/or nectar secretion in the genus, particularly among closely related species. Here we investigated nectary morphology, nectar quality, and nectar production dynamics in flowers of Pedicularis section Cyathophora. We found a conical floral nectary at the base of the ovary in species of the rex-thamnophila clade. Stomata were found on the sudace of the nectary, and copious starch grains were detected in the nectary tissues. In contrast, a semi-annular nectary was found in flowers of the species of the superba clade. Only a few starch grains were observed in tissues of the semi-annular nectary, and the nectar sugar concentration in these flowers was much lower than that in the flowers of the rexthamnophila clade. Our results indicate that the floral nectary has experienced considerable morphological, structural, and functional differentiation among closely related species of Pedicularis. This could have affected nectar production, leading to a shift of the pollination mode. Our results also imply that variation of the nectary morphology and nectar production may have played an important role in the speciation of sect. Cyathophora.

Morphological study of floral nectaries in Euonymus and the probable origin of the echinate fruit surface

A conspicuous nectary disk is common but has a distinguishing morphology in the cosmopolitan genus Euonymus. Our study focuses on the morphology of floral nectaries in 21 representatives of Euonymus and Glyptopetalum. Two main types of nectaries were documented: a mix of inter-and extrastaminal nectaries existed between the corolla and the stigma, while the intrastaminal nectaries were distributed between the stigma and the stamen bases. The main route of nectar release in Euonymus is via modified stomata, and different nectarostomata locations were observed: in depressions, slightly raised above the epidermal surface or at the same level as the epidermis. Floral nectaries in E. sect. Echinococcus species developed into the protrusions on the fruit surface at the later stage. The development of nectaries not only explained the mystery of the origin of the echinate fruit surface, but also showed that differences in fruit surface might be inappropriate for use in infrageneric classification. These discoveries inform morphological observations of floral nectaries in Euonymus.

<i>Rhizobium</i>alters inducible defenses in broad bean, <i>Vicia faba</i>

Conversion of inorganic nitrogen by mutualistic nitrogen-fixing bacteria is essential for plant growth and reproduction, as well as the development of chemical and mechanical defenses. It is unclear, however, how these bacteria alter co-occurring symbioses at higher trophic levels;e.g., extrafloral nectary (EFN) induction, in response to herbivory, to attract defensive mutualists. We hypothesized that plants colonized by nitrogen-fixing bacteria would mount a larger inducible, defensive response than plants lacking symbioses, as defensive traits are costly. We predicted that bean plants, Vicia faba L., harboring Rhizobium leguminosarum bv. viciae Frank would produce more EFNs upon leaf damage, than plants lacking the symbionts, as EFN induction in V. faba is resource-dependent. Here we report that V. faba colonized by R. leguminosarum produced similar numbers of EFNs as did plants without symbionts. Plants with symbionts, however, produced significantly fewer EFNs over 1 week in response to leaf damage, than those without leaf damage. As such, nitrogen-fixing bacteria may not always benefit the host plant, but rather, the utility of these bacteria may be dependent on the prevailing ecological conditions.