Functional Ecology of External Secretory Structures in Rivea ornata (Roxb.) Choisy (Convolvulaceae)

Abstract

Plants have evolved numerous secretory structures that fulfill diverse roles and shape their interactions with other organisms. Rivea ornata (Roxb.) Choisy (Convolvulaceae) is one species that possesses various external secretory organs hypothesized to be ecologically important. This study, therefore, aimed to investigate five secretory structures (nectary disc, petiolar nectaries, calycinal glands, staminal hairs, and foliar glands) using micromorphology, anatomy, histochemistry, and field observations of plant–animal interactions in order to assess the functional contributions of these structures. Results show that the nectary disc and petiolar nectaries are complex working units consisting of at least epidermis and ground tissue, while the other structures are glandular trichomes. Various groups of metabolites (lipids, phenolic compounds, polysaccharides, terpenoids, flavonoids, and alkaloids) were detected in all structures, while starch grains were only found in the nectary disc, petiolar nectaries, and their adjacent tissues. Integrating preliminary observation of animal visitors with micromorphological, anatomical, and histochemical results, two hypotheses are proposed: (I) nectary disc and staminal hairs are important for pollination as they potentially attract and reward floral visitors, and (II) petiolar nectaries, calycinal glands, and foliar glands contribute to plant defense. Specifically, petiolar nectaries and calycinal glands provide protection from herbivores via guard ants, while calycinal and foliar glands may use plant metabolites to help prevent tissue damage from dehydration and insolation.

Does the Floral Nectary in Dracocephalum moldavica L. Produce Nectar and Essential Oil? Structure and Histochemistry of the Nectary

“…The histochemical and fluorescence assays showed the presence of lipid compounds (total lipids, acidic, and neutral lipids) and phenolic compounds (total phenols, phenolic acids, and flavonoids) in the tissues and glandular trichomes of the D. moldavica nectary. Various authors also reported the presence of similar groups of metabolites in nectaries of other plant species [ 57 , 58 , 59 , 60 ]. Similar to the present findings, these researchers showed that the metabolites were located in the nectary epidermis and/or parenchyma; next, the compounds penetrated into the secreted nectar.…”

Near extinct Argyreia versicolor and rare Argyreia mekongensis are dependent on carpenter bee pollinators

“…Our pollinator observations indicate that both A. versicolor and A. mekongensis are pollinated by carpenter bees. Previous studies have generally reported that Convolvulaceae species are mainly pollinated by bees ( Galetto and Bernadello 2004 ; Maimoni-Rodella and Yanagizawa 2007 ; Pick and Schlindwein 2011 ; Hassa et al 2023 ) or by bees and butterflies ( Hassa et al 2020 ; Jirabanjongjit et al 2021 ) or by hawkmoths ( Willmott and Burquez 1996 ; McMullen 2009 ; Chitchak et al 2022 ). Pollination studies of Argyreia are scarce compared to sister genera such Ipomoea , but Chitchak et al (2018) did report that Xylocopa nasalis visits Argyreia gyrobracteata and receives pollen on its head.…”

Plant Secondary Metabolites: The Weapons for Biotic Stress Management

“…Extrafloral nectaries are also considered as storage organs for secondary metabolites. Cassava, tapioca, passiflora, cotton, cashew nut trees, and several members of the Rosaceae have been reported to emit secondary metabolites from extra floral nectaries that aid in luring predators of various pest species [ 108 , 109 ].…”