Abstract
Tocoyena formosa has a persistent floral nectary that continues producing nectar throughout flower and fruit development. This plant also presents an intriguing non-anthetic nectary derived from early-developing floral buds with premature abscised corolla. In this study, we characterize the structure, morphological changes, and functioning of T. formosa floral nectary at different developmental stages. We subdivided the nectary into four categories based on the floral and fruit development stage at which nectar production started: (i) non-anthetic nectary; (ii) anthetic nectary, which follows the regular floral development; (iii) pericarpial nectary, derived from pollinated flowers following fruit development; and (iv) post-anthetic nectary that results from non-pollinated flowers after anthesis. The nectary has a uniseriate epidermis with stomata, nectariferous parenchyma, and vascular bundles, with a predominating phloem at the periphery. The non-anthetic nectary presents immature tissues that release the exudate. The nectary progressively becomes more rigid as the flower and fruit develop. The main nectary changes during flower and fruit development comprised the thickening of the cuticle and epidermal cell walls, formation of cuticular epithelium, and an increase in the abundance of calcium oxalate crystals and phenolic cells near the vascular bundles. Projections of the outer periclinal walls toward the cuticle in the post-anthetic nectary suggest nectar reabsorption. The anatomical changes of the nectary allow it to function for an extended period throughout floral and fruit development. Hence, T. formosa nectary is a bivalent secretory structure that plays a crucial role in the reproductive and defensive interactions of this plant species.
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Acknowledgements
This study was carried out as part of the JVI master’s thesis at the Programa de Pós-graduação em Ciências Biológicas (Botânica), IBB, UNESP. We thank J. V. Alcantara, E. Dal Farra, L. Hachuy Filho, C. S. Ballarin, P. Sanz Veiga, and Heloíza Cassola for assistance during field work and sampling.
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This study was supported by the “Coordenação de Aperfeiçoamento de Pessoal de Nível Superior”-Brazil (CAPES, Finance code 001). This work received financial support from São Paulo Research Foundation (FAPESP, grant number 2021/13392–0) to SRM and Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) (FWA, grant numbers 484469/2013–4 and 308559/2022–3; SRM, grant 308982/2020–7).
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FWA, JVI, YC, and SRM conceived and designed the research. JVI and FWA carried out field work and sampling. JVI and YC carried out the laboratory work. YC, JVI, and SRM conducted the data analysis and wrote the original draft. FWA, JVI, YC, and SRM reviewed and edited.
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Izquierdo, J.V., Canaveze, Y., Machado, S.R. et al. Anatomical, histochemical, and developmental approaches reveal the long-term functioning of the floral nectary in Tocoyena formosa (Rubiaceae). Sci Nat 111, 25 (2024). https://doi.org/10.1007/s00114-024-01909-5
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DOI: https://doi.org/10.1007/s00114-024-01909-5