First description of extrafloral nectaries in Opuntia robusta (Cactaceae): Anatomy and ultrastructure.

Autor: Sandoval-Molina MA; Research Group in Ecology and Evolutionary Biology, Department of Natural Sciences, Autonomous University of the State of Mexico, Toluca, Estado de México, México.; Instituto de Ecología, El Haya, Xalapa, Veracruz, México., Zavaleta-Mancera HA; Unidad de Microscopía Electrónica, Postgrado en Botánica, Colegio de Postgraduados, Campus Montecillo, Montecillo, Texcoco, Estado de México., León-Solano HJ; Research Group in Ecology and Evolutionary Biology, Department of Natural Sciences, Autonomous University of the State of Mexico, Toluca, Estado de México, México.; Graduate Program in Agricultural Sciences and Natural Resources (PCARN), Autonomous University of the State of Mexico, Toluca, Estado de México, México., Solache-Ramos LT; Research Group in Ecology and Evolutionary Biology, Department of Natural Sciences, Autonomous University of the State of Mexico, Toluca, Estado de México, México.; Graduate Program in Agricultural Sciences and Natural Resources (PCARN), Autonomous University of the State of Mexico, Toluca, Estado de México, México., Jenner B; Evidence Generation & Clinical Research RB, Hull, United Kingdom., Morales-Rodríguez S; Instituto de Ecología, El Haya, Xalapa, Veracruz, México., Patrón-Soberano A; Instituto Potosino de Investigación Científica y Tecnológica, San Luis Potosí, México., Janczur MK; Research Group in Ecology and Evolutionary Biology, Department of Natural Sciences, Autonomous University of the State of Mexico, Toluca, Estado de México, México.; Graduate Program in Agricultural Sciences and Natural Resources (PCARN), Autonomous University of the State of Mexico, Toluca, Estado de México, México.
Jazyk: angličtina
Zdroj: PloS one [PLoS One] 2018 Jul 17; Vol. 13 (7), pp. e0200422. Date of Electronic Publication: 2018 Jul 17 (Print Publication: 2018).
DOI: 10.1371/journal.pone.0200422
Abstrakt: To our knowledge, there are no studies about the structure and ecological function of extrafloral nectaries (EFNs) in Opuntia robusta. This is the first description of EFNs in O. robusta, where young spines have an interesting structure and a secreting function, which are different from EFNs described in other Cactaceae species. 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. Young cladodes develop areoles with modified and secretory spines as EFNs only active during the early growth phase. EFNs are non-vascularized structures, with no stomata, that consist of a basal meristematic tissue, a middle elongation region, and an apical secretory cone formed by large globular epidermal cells, containing nectar and medullar elongated cells. We observed the presence of Golgi apparatus, vesicles and plastids in the medullar and sup-epidermal cells of the spine. We propose that the nectar is stored in the globular cells at the apex of the spine and secreted by breaking through the globular cells or by pores. We recorded a more frequent presence of ants on younger cladode sprouts producing young secreting spines: this result is parallel with the predictions of Optimal Defense Hypothesis, which states that younger plant organs should be better defended than older ones because their loss produces a higher fitness impairment. Although Diaz-Castelazo's hypothesis states that a more complex structure of EFNs correlates with their lower among-organs dispersion, comparing to less complex EFNs, non-vascularized structure of EFNs in O. robusta is not associated with their higher among-organs dispersion likened to O. stricta, which produces vascularized EFNs. We provide evidence that this characteristic is not a good taxonomic feature of Opuntia genus. Moreover, the comparison of EFNs of O. robusta and O. stricta suggests that the hypothesis of Diaz-Castelazo should be revised: it is rather a rule but not a law.
Competing Interests: The authors have declared that no competing interests exist.
Databáze: MEDLINE
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