Abstract
Mabea fistulifera, a species pollinated mainly by diurnal and nocturnal vertebrates, presents pendulous inflorescences with approximately 70 pairs of nuptial nectaries (NNs). These NNs exude voluminous nectar drops that defy gravity, remaining exposed at the inflorescence for more than a day. We aimed to investigate the NN secretory process and the unique nectar presentation of M. fistulifera. NNs and their exudate were collected at different secretory stages and submitted to structural studies and chemical analysis. The epidermis is devoid of stomata and constitutes the main site of synthesis for non-sugar metabolites found on nectar and nectar-coating film. Nectary parenchyma presents few small starch grains, and vascular strands are distributed until the nectary parenchyma cells close to the epidermis. Vascular tissues at the nectary parenchyma seem to provide sugar and water for the nectar. A film composed of lipids, alkaloids, and proteins covers the nectar drops. The film guarantees the nectar offering for several hours, as it minimizes water loss and prevents falls by gravitational action. The release of large nectar drops is intrinsically linked to the NN anatomical traits and the exudate composition. Low sugar concentration and predominance of hexoses in M. fistulifera nectar are essential for maintaining nectar exudation for many hours, which results in the visitation of a broad spectrum of pollinators.
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Acknowledgements
We thank the Center of Microscopy at the Universidade Federal de Minas Gerais (http://www.microscopia.ufmg.br) for providing the equipment and technical support for electron microscopy. We also thank the Laboratório de Nutrição e Metabolismo de Plantas at the Universidade Federal de Viçosa and Dr. Leandro E. Morais for the help in the chemical analysis and Dr. Ítalo S.C. Granato for collaborating with the statistical data.
Funding
This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior, Brazil (CAPES, Finance Code 001). E.A.S. Paiva thanks the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq, Brazil, processes 307353/2021–4) for research grants. The Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG) has provided a masters’ scholarship to A.L. Almeida.
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All authors contributed to the study conception and design; MCV advised the first author. Material preparation, data collection, and analysis were performed by ALA. The first draft of the manuscript was written by ALA, EASP, MFV, and MCV. All authors read and approved the final manuscript.
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Almeida, A.L., Paiva, E.A.S., Vieira, M.F. et al. How can structure and nectar composition explain the secretory process in super productive nuptial nectaries of Mabea fistulifera Mart. (Euphorbiaceae)?. Protoplasma 260, 935–947 (2023). https://doi.org/10.1007/s00709-022-01824-4
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DOI: https://doi.org/10.1007/s00709-022-01824-4