Quantitative Assessment of Nectar Microbe-Produced Volatiles

Abstract

Nectar microbe-produced volatiles can contribute to floral blends and modify pollinator preference for flowers. Identifying and describing the compounds that may underlie this effect is a key goal. Semi-quantitative or quantitative data is often critical for chemical ecology investigations, given that biotic responses (i.e., insects or plants) can fluctuate with concentration, relative ratios, or composition of the emitted volatile profiles. However, field-based, in situ microbial volatile detection and quantification is difficult due to the small scale of the nectar microhabitat. Laboratory-based inoculations of bulk synthetic nectars are useful for screening weakly-abundant and difficult to analyze volatiles, which may be crucial in eliciting responses. Despite the limitations of this approach, it allows rapid identification of target molecules for further validation with bioassays. Targeted analytical methods to identify or quantify semiochemicals may then be developed and validated for field tests. Here, we report the first quantitative assessment of microbe volatile emission in laboratory-based tests with synthetic nectar. We also review briefly solid-phase microextraction collection and gas-chromatography data interpretation. Nectar microbe interactions with plants and insects offer opportunities for agricultural improvement, and a selection of potential uses are highlighted.

Differences in Floral Scent and Petal Reflectance Between Diploid and Tetraploid Chamerion angustifolium

“…Both 2-nonanone and 2-hexen-1-ol were emitted in higher amounts from diploids and are common floral scents (Knudsen et al, 2006). Interestingly, 2nonanone is also a component of the Bombus terrestris queen pheromone (Krieger et al, 2006) and can be produced by nectar fungi (Rering et al, 2018). Because our plants were grown in the greenhouse without access to pollinators to inoculate the nectar, it is unlikely that 2-nonanone was nectar fungi-produced.…”

Yeast–Bacterium Interactions: The Next Frontier in Nectar Research

“…Yeasts and bacteria may also differentially alter secondary metabolites in nectar, including volatile compounds [15,40]. Nectar microorganisms can produce blends of volatile compounds that attract or deter pollinators [15,40,41]. In turn, this effect on pollinators might have consequences on microbial and plant fitness and the dispersal of microorganisms from flower to flower [15].…”

“…Farnesol, a major quorum sensing molecule in diverse fungal species[41,64,65], is also a component of insect pheromones that mediate foraging, sexual attraction, and other behavioral responses, and has been found in the flowers of some plants[66][67][68]. Even though the study of semiochemical production by nectar microbes is still in its infancy[15,40,42] and, to our knowledge, farnesol release by nectar yeasts remains to be demonstrated, it seems possible that microbe-microbe communication changes floral visitors' behavior as a side effect.Horizontal gene transferHorizontal gene transfer is prevalent in plant-associated bacteria[69,70]. Numerous cases of horizontal gene transfer from bacteria to fungi have also been described, although it seems less frequent than horizontal gene transfer among bacteria[70,71].…”