Fiber‐optic refractometer for in vivo sugar concentration measurements of low‐nectar‐producing flowers

Abstract

Summary Sugar concentration in floral nectars is an assessment required in several diverse fields of application. The widely used analysis, consisting of nectar extraction with a microcapillary and sugar concentration measurement with a light refractometer, is not reliable when the nectar is secreted in small quantities, unextractable with a microcapillary. Ancillary methods adopted in such cases are destructive, rather complicated and often provide much less precise and accurate results. The microscopic‐size, low cost and biocompatibility of optical fibers were exploited to deliver light directly inside the flower with minimal invasiveness and measure instantaneously the refractometric properties of the nectar without extracting it. After comparing the new and old methods using two known nectariferous species, the new approach was validated on Primula palinuri, whose nectar is unextractable with microcapillaries. The fiber‐optic probe was able to measure the nectar refractive index in P. palinuri flowers making it possible to highlight a previously undetected significant trend of the sugar concentration throughout the long anthesis of the single flowers. Changes in nectar concentrations are similar in both longistylous and brevistylous flowers. The fiber‐optic refractometer is an advancement of light refractometer analysis. Further customization of the laboratory set‐up into portable equipment will boost applications.

Elevated ozone and carbon dioxide affects the composition of volatile organic compounds emitted by Vicia faba (L.) and visitation by European orchard bee (Osmia cornuta)

“…The ºBx is read by holding the device against light to determine its refractive index. The refractive index of nectar is used as a measure of sugar equivalent in the solution [ 49 ].…”

Beyond Beer's Law: Why the Index of Refraction Depends (Almost) Linearly on Concentration

“…This linear change has been confirmed numerous times experimentally and builds the foundation for the determination of concentrations by refractive index sensing and well-established methods like, e. g., sugar concentration determination by refractometer. [12] For comparably weak oscillators, like most vibrations in organic and biological materials, linearity based on Equation (6) could be assumed over the whole concentration range. From Figure 1, upper panel, we see that linearity holds to about c � 8 mol L À 1 (comparison of black and pink curve, absorbance value at 1700 cm À 1 ).…”

Onion (Allium cepa L.) hybrid seed production: Sugar content variation during the flowering period

“…In each flower, nectar accumulates at the base of the ovary (Currah, 1990). Although the quantity of nectar per single flower is insignificant (0.54–0.84 μl per floret per d; Hagler, 1990), an inflorescence produces enough nectar to be attractive to insect pollinators (Aronne & Malara, 2019).…”

“…Floral nectar is a plant secretion made of a water solution containing sugars, but also amino acids, proteins, lipids, phenols, elemental species, alkaloids, terpenes, vitamins, and other antioxidants (Arone & Malara, 2019). It is recognized as an important reward for pollinators and its production increases reproduction in many plants (Solhaug et al., 2019).…”