Abstract
Buds usually possess mechanical or chemical protection and may also have secretory structures. We discovered an intricate secretory system in Ouratea castaneifolia (Ochnaceae) related to the protection of buds and young leaves. We studied this system, focusing on the distribution, morphology, histochemistry, and ultrastructure of glands during sprouting. Samples of buds and leaves were processed following the usual procedures for light and electron microscopy. Overlapping bud scales protect dormant buds, and each young leaf is covered with a pair of stipules. Stipules and scales possess a resin gland, while the former also possess an extrafloral nectary. Despite their distinct secretions, these glands are similar and comprise secreting palisade epidermis. Young leaves also possess marginal colleters. All the studied glands shared some structural traits, including palisade secretory epidermis and the absence of stomata. Secretory activity is carried out by epidermal cells. Functionally, the activity of these glands is synchronous with the young and vulnerable stage of vegetative organs. This is the first report of colleters and resin glands for O. castaneifolia. We found evidence that these glands are correlated with protection against herbivores and/or abiotic agents during a developmental stage that precedes the establishment of mechanical defenses.
Highlights
The botanical family Ochnaceae has a pantropical distribution, comprising 27 genera and approximately 500 species [1], with its center of diversity being the Neotropics
Many aspects of secretion in the family are still poorly understood. Considering this knowledge gap, we investigated the anatomy, histochemistry, and ultrastructure of the colleters, nectaries, and resin glands present in the buds and developing leaves of Ouratea castaneifolia (DC.) Engl., an arboreal-shrub species of the Cerrado and Brazilian semi-deciduous forests [18]
Flowering occurs at the end of leaf sprouting, and the vegetative buds go into dormancy, remaining in a resting state until the annual vegetative cycle
Summary
The botanical family Ochnaceae has a pantropical distribution, comprising 27 genera and approximately 500 species [1], with its center of diversity being the Neotropics. The Ouratea genus, with about 300 species, is the largest and most diverse of the family [2]. Secretion and secretory products seem to be important features for species of Ouratea. Representatives of this genus possess a pair of conspicuous stipules, in which there is, at least for some species, an extrafloral nectary (EFN) on the abaxial face [5]. Species of Ouratea are a rich source of flavonoids and biflavonoids, and show potential as constituents of medicines; triterpenes, diterpenes, steroids, monosaccharides, and triacylglycerides are common in this plant group [6]
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