Abstract
The genus Hymenaea is characterized by a great diversity of secretory structures, but there are no reports of colleters yet. The objectives of this study are to report the occurrence and describe the origin and structure of colleters in Hymenaea stigonocarpa Mart. ex Hayne. Shoot apex samples were collected, fixed, and processed for light microscopy, scanning electron microscopy, and transmission electron microscopy as per usual methods. Colleters occur predominantly on the stipule's adaxial side. These structures are found at the base on a narrow strip, corresponding to the median vein up to half the length of the stipule. When present on the abaxial side, they are concentrated at the base and restricted to the margins. Colleters develop from the protoderm; they are elongate and club-shaped. Their body has no stratification; their surface cells differ from the inner cells only in position and presence of cuticle. Colleter cells have thin walls, dense cytoplasm, large nuclei, many mitochondria, rough endoplasmic reticulum, and abundant dictyosomes. Histochemical tests with Ruthenium red showed pectic compounds in the cytosol. In H. stigonocarpa, colleter arrangement is compatible with the hypothesis that they protect shoot apex. In this species, protection is reinforced by the sheath formed by the stipule pairs.
Highlights
Colleters are considered to be glandular trichomes that produce a mucilaginous or resinous substance and are present in the shoot apex (Fahn 1990)
This study presents the first record of colleters in the genus Hymenaea, a member of the FabaceaeCaesalpinioideae
In H. stigonocarpa, stipules encase the innermost stipule and the young leaf in a repetitive pattern, protecting successive leaf primordia and the shoot apex, in a rare arrangement (Lee and Langenheim 1975); this indicates the protective role of these structures as suggested by Lubbock (1890)
Summary
Colleters are considered to be glandular trichomes that produce a mucilaginous or resinous substance and are present in the shoot apex (Fahn 1990). These structures differentiate early and their function is to protect the shoot meristem and leaf primordia (Mueller 1985, Thomas and Dave 1990, Thomas 1991). This study presents the first record of colleters in the genus Hymenaea, a member of the FabaceaeCaesalpinioideae This genus contains about 13 species in tropical America and is characterized by a great diversity of secretory structures, including nectaries and resin secretory cavities (Lee and Langenheim 1975). Origin, distribution, and structure of colleters in this species
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