Replication Data for: First description of extrafloral nectaries in Opuntia robusta (Cactaceae): anatomy and ultrastructure

The presence and structure of extrafloral nectaries (EFNs) in Opuntia robusta had not been investigated. We observed ants collecting nectar from young areoles. We recorded ants' behavior, quantified their presence on cladode sprouts, and associated ant number with sprouts size, air humidity, temperature, and daytime. We used light, scanning-electron, and transmission-electron microscopy to examine morphology, anatomy, and ultrastructure of the secretory spines in areoles in female and hermaphrodite individuals of O. robusta. Ants preferred narrower cladode sprouts with younger spines. Young cladodes develop areoles with modified and secretory spines as EFNs only active during the early growth phase of female and hermaphrodite individuals. EFNs are non-vascularized structures, with no stomata, that consist of three distinct tissues: a basal meristematic tissue; a middle elongation region; and an apical secretory cone (asc) formed by large globular epidermal cells, of sac shape, containing nectar and medullar elongated cells. TEM observations indicated the presence of Golgi apparatus, vesicles and plastids in the medullar and sup-epidermal cells of the asc, transporting nectar to the epidermal secretory cells. The nectar is transported through plasmodesmata, and then stored on the asc cells, to be secreted by breaking through the globular cells and pores. Diaz-Castelazo’s hypothesis states that more complex EFNs correlate with their lower among-organs dispersion, comparing to less complex EFNs. However, non-vascularized (less complex) structure of EFNs in O. robusta is not associated with their higher among-organs dispersion compared to O. stricta, which produces vascularized (more complex) EFNs, as showed by Diaz Castelazo et al. Our study gives an evidence that this character is not a good taxonomic feature of Opuntia genus. The presence of ants on smaller cladode sprouts is parallel with the prediction of Optimal Defense Hypothesis, which states that younger organs should be better defended than older and less valuable organs.