title: A light in the shadow: the use of Lucifer Yellow technique to demonstrate nectar reabsorption.
abstract: BACKGROUND
  Nectar reabsorption is a widely known phenomenon, related to the strategy of resource-recovery and also to maintain the nectar homeostasis at the nectary. The method currently performed to demonstrate nectar being reabsorbed involves the use of radioactive tracers applied to the nectary. Although this method works perfectly, it is complex and requires specific supplies and equipment. Therefore, here we propose an efficient method to obtain a visual demonstration of nectar reabsorption, adapting the use of Lucifer Yellow CH (LYCH), a fluorescent membrane-impermeable dye that can enter the vacuole by endocytosis.
  
  
  RESULTS
  We applied a LYCH solution to the floral nectary (FN) of Cucurbita pepo L., which is a species known for its ability of nectar reabsorption, and to the extrafloral nectary (EFN) of Passiflora edulis Sims which does not reabsorb the secreted nectar. In all tests performed, we observed that LYCH stained the nectary tissues differentially according to the reabsorption ability of the nectary. The treated FN of C. pepo presented a concentrated fluorescence at the epidermis that decreased at the deeper nectary parenchyma, until reaching the vascular bundles, indicating nectar reabsorption in the flowers of the species. In contrast, treated EFN of P. edulis presented fluorescence only at the cuticle surface, indicating that nectar is not reabsorbed by that particular tissue.
  
  
  CONCLUSIONS
  LYCH is an efficient marker to demonstrate nectar reabsorption.
authors.affiliation: Programa de Pós-Graduação em Biodiversidade Vegetal e Meio Ambiente, Instituto de Botânica, C, Postal 68041, São Paulo, SP, Brazil. cardoso.poliana@gmail.com.
authors.forename: Poliana
authors.initials: P
authors.lastname: Cardoso-Gustavson
authors.forename: João Marcelo
authors.initials: JM
authors.lastname: Robazzi Bignelli Valente Aguiar
authors.forename: Emerson
authors.initials: E
authors.lastname: Ricardo Pansarin
authors.forename: Fábio
authors.initials: F
authors.lastname: de Barros