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Histochemical results obtained from staminal hairs of Rivea ornata. (A) Unstained staminal hairs. (B) Sudan black B test for total lipids. (C) Neutral red fluorochrome test for total lipids. (D) Ferric chloride test for phenolic compounds. (E) Potassium dichromate test for phenolic compounds. (F) Lugol's iodine test for starch. (G) Periodic acid-Schiff's reagent (PAS) test for neutral polysaccharides. (H) Ruthenium red test for acidic polysaccharides. (I) Mercuric bromophenol blue test for proteins. (J) Nadi reagent test for terpenoids. (K) Naturstoff reagent A under fluorescent microscopy detecting flavonoids. (L) Dragendorff reagent test for alkaloids. (M) Wagner's reagent test for alkaloids. (N) UV autofluorescence of staminal hairs. Note: (B-E,G,H,J-M) show positive reactions, while (F,I) show negative reactions. Abbreviations: h, head; p, pollen grain; s, stalk. Scale bars 200 μm.
Source publication
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...
Contexts in source publication
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... histochemical assays revealed that the secretory structures in R. ornata produce various groups of metabolites, as all examined compounds tested positive, with the exception of proteins ( Table 1 and Figures 5-9). Lipids appear to be restricted to structural layers such as cell walls, while phenolic compounds, terpenoids, flavonoids, and alkaloids are mainly found in substances that accumulate in cytoplasmic components. ...
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... appear to be restricted to structural layers such as cell walls, while phenolic compounds, terpenoids, flavonoids, and alkaloids are mainly found in substances that accumulate in cytoplasmic components. Polysaccharides, in general, occur in both cell walls and cell contents (Table 1 and Figures 5-9). Additionally, starch grains were found only in the nectary disc, and only sparsely (Table 1 and Figure 5L,M), but they were also detected in abundance in parenchyma cells of the receptacle ( Figure 5L,M) and in cells near petiolar nectaries ( Figure 6H,I). ...
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... autofluorescence under UV wavelengths was also mainly found in cells in the abaxial regions ( Figure 5BB,CC). In the staminal hairs, positive histochemical results were found in both the head and stalk regions, but they generally showed different degrees of chromatic reaction (Table and Figure 9). Only phenolic compounds were absent from the head of the hairs (Table and Figure 9D,E). ...
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... the staminal hairs, positive histochemical results were found in both the head and stalk regions, but they generally showed different degrees of chromatic reaction (Table and Figure 9). Only phenolic compounds were absent from the head of the hairs (Table and Figure 9D,E). For lipids, while Sudan black B gave relatively indistinct positive reac tions in both the head and stalk regions, neutral red fluorochrome results were noticeably evident at the head ( Figure 9B,C). ...
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... phenolic compounds were absent from the head of the hairs (Table and Figure 9D,E). For lipids, while Sudan black B gave relatively indistinct positive reac tions in both the head and stalk regions, neutral red fluorochrome results were noticeably evident at the head ( Figure 9B,C). For neutral polysaccharides, the head stained magent but the stalk stained red ( Figure 9G). ...
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... lipids, while Sudan black B gave relatively indistinct positive reac tions in both the head and stalk regions, neutral red fluorochrome results were noticeably evident at the head ( Figure 9B,C). For neutral polysaccharides, the head stained magent but the stalk stained red ( Figure 9G). A similar result was observed for terpenoids, in which substances stored in the head turned violet or blue, but the wall of the head and the stalk were solely dark blue ( Figure 9J). ...
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... neutral polysaccharides, the head stained magent but the stalk stained red ( Figure 9G). A similar result was observed for terpenoids, in which substances stored in the head turned violet or blue, but the wall of the head and the stalk were solely dark blue ( Figure 9J). The test for acidic polysaccharides generally showed patterns of positive staining in the head, but some heads were completely stained some were stained only at the area attaching to the stalk, and some were entirely un stained ( Figure 9H). ...
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... similar result was observed for terpenoids, in which substances stored in the head turned violet or blue, but the wall of the head and the stalk were solely dark blue ( Figure 9J). The test for acidic polysaccharides generally showed patterns of positive staining in the head, but some heads were completely stained some were stained only at the area attaching to the stalk, and some were entirely un stained ( Figure 9H). Both parts of the staminal hairs emitted dim blue autofluorescenc under UV wavelengths ( Figure 9N). ...
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... test for acidic polysaccharides generally showed patterns of positive staining in the head, but some heads were completely stained some were stained only at the area attaching to the stalk, and some were entirely un stained ( Figure 9H). Both parts of the staminal hairs emitted dim blue autofluorescenc under UV wavelengths ( Figure 9N). In the staminal hairs, positive histochemical results were found in both the head and stalk regions, but they generally showed different degrees of chromatic reaction (Table 1 and Figure 9). ...
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... parts of the staminal hairs emitted dim blue autofluorescenc under UV wavelengths ( Figure 9N). In the staminal hairs, positive histochemical results were found in both the head and stalk regions, but they generally showed different degrees of chromatic reaction (Table 1 and Figure 9). Only phenolic compounds were absent from the head of the hairs (Table 1 and Figure 9D,E). ...
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... the staminal hairs, positive histochemical results were found in both the head and stalk regions, but they generally showed different degrees of chromatic reaction (Table 1 and Figure 9). Only phenolic compounds were absent from the head of the hairs (Table 1 and Figure 9D,E). For lipids, while Sudan black B gave relatively indistinct positive reactions in both the head and stalk regions, neutral red fluorochrome results were noticeably evident at the head ( Figure 9B,C). ...
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... phenolic compounds were absent from the head of the hairs (Table 1 and Figure 9D,E). For lipids, while Sudan black B gave relatively indistinct positive reactions in both the head and stalk regions, neutral red fluorochrome results were noticeably evident at the head ( Figure 9B,C). For neutral polysaccharides, the head stained magenta but the stalk stained red ( Figure 9G). ...
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... lipids, while Sudan black B gave relatively indistinct positive reactions in both the head and stalk regions, neutral red fluorochrome results were noticeably evident at the head ( Figure 9B,C). For neutral polysaccharides, the head stained magenta but the stalk stained red ( Figure 9G). A similar result was observed for terpenoids, in which substances stored in the head turned violet or blue, but the wall of the head and the stalk were solely dark blue ( Figure 9J). ...
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... neutral polysaccharides, the head stained magenta but the stalk stained red ( Figure 9G). A similar result was observed for terpenoids, in which substances stored in the head turned violet or blue, but the wall of the head and the stalk were solely dark blue ( Figure 9J). The test for acidic polysaccharides generally showed patterns of positive staining in the head, but some heads were completely stained, some were stained only at the area attaching to the stalk, and some were entirely unstained ( Figure 9H). ...
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... similar result was observed for terpenoids, in which substances stored in the head turned violet or blue, but the wall of the head and the stalk were solely dark blue ( Figure 9J). The test for acidic polysaccharides generally showed patterns of positive staining in the head, but some heads were completely stained, some were stained only at the area attaching to the stalk, and some were entirely unstained ( Figure 9H). Both parts of the staminal hairs emitted dim blue autofluorescence under UV wavelengths ( Figure 9N). ...
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... test for acidic polysaccharides generally showed patterns of positive staining in the head, but some heads were completely stained, some were stained only at the area attaching to the stalk, and some were entirely unstained ( Figure 9H). Both parts of the staminal hairs emitted dim blue autofluorescence under UV wavelengths ( Figure 9N). ...
Citations
... 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]. ...
The rise in global temperature also favors the multiplication of pests and pathogens, which calls into question global food security. Plants have developed special coping mechanisms since they are sessile and lack an immune system. These mechanisms use a variety of secondary metabolites as weapons to avoid obstacles, adapt to their changing environment, and survive in less-than-ideal circumstances. Plant secondary metabolites include phenolic compounds, alkaloids, glycosides, and terpenoids, which are stored in specialized structures such as latex, trichomes, resin ducts, etc. Secondary metabolites help the plants to be safe from biotic stressors, either by repelling them or attracting their enemies, or exerting toxic effects on them. Modern omics technologies enable the elucidation of the structural and functional properties of these metabolites along with their biosynthesis. A better understanding of the enzymatic regulations and molecular mechanisms aids in the exploitation of secondary metabolites in modern pest management approaches such as biopesticides and integrated pest management. The current review provides an overview of the major plant secondary metabolites that play significant roles in enhancing biotic stress tolerance. It examines their involvement in both indirect and direct defense mechanisms, as well as their storage within plant tissues. Additionally, this review explores the importance of metabolomics approaches in elucidating the significance of secondary metabolites in biotic stress tolerance. The application of metabolic engineering in breeding for biotic stress resistance is discussed, along with the exploitation of secondary metabolites for sustainable pest management.
... 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. ...
Dracocephalum moldavica is an aromatic plant with a lemon scent and versatile use. Its flowers produce large amounts of nectar, which is collected by bees and bumblebees. The aim of the study was to investigate the structure of the floral nectary in this melliferous plant, which has not been analysed to date. The analyses were carried out with the use of light, fluorescence, scanning electron, and transmission electron microscopy, as well as histochemical techniques. The four-lobed nectary with a diameter of 0.9–1.2 mm and a maximum height of 1.2 mm is located at the ovary base; one of its lobes is larger than the others and bears 20–30 nectarostomata and 8–9 glandular trichomes. The histochemical assays revealed the presence of essential oil and phenolic compounds in the nectary tissues and in glandular trichomes. The nectary tissues are supplied by xylem- and phloem-containing vascular bundles. The nectariferous parenchyma cells have numerous mitochondria, plastids, ribosomes, dictyosomes, ER profiles, vesicles, thin cell walls, and plasmodesmata. Starch grains are present only in the tissues of nectaries in floral buds. The study showed high metabolic activity of D. moldavica nectary glands, i.e., production of not only nectar but also essential oil, which may increase the attractiveness of the flowers to pollinators, inhibit the growth of fungal and bacterial pathogens, and limit pest foraging.
