Testing the optimal defense hypothesis in Stryphnodendron adstringens (Fabaceae,Mimosoideae) leaves: the role of structure,number, position and nectar composition of extrafloral nectaries

Stryphnodendron adstringens is a common Cerrado tree that possesses extrafloral nectaries (EFNs) on its leaves, which are located at the base and apex of the rachis and along the secondary veins. The position of EFNs and their nectar production can be affected by defense strategies because plant organs possess different values and herbivory vulnerability. Here we aimed to elucidate anatomy, histochemistry, nectar composition and EFN number on leaves of S. adstringens in the light of the optimal defense hypothesis. We found a convergence on anatomy and histochemical characterization because the three studied types of EFNs have epidermis, secretory parenchyma and vascular tissue, showing phenolic compounds and polysaccharides in the secretory parenchyma cells. The nectar contained glucose, fructose and sucrose, which attract ants of the Camponotus and Cephalotes genus. We found differences in the number of EFNs along the secondary veins and in the nectar composition between EFNs located at the base and apex of the rachis of the leaf. The number of EFNs on the secondary veins increases from the base to the apex, suggesting a strategy to induce ant patrolling over the entire leaf region. EFNs at the base secreted more nectar, which should be related to the protection of the leaf base, which is the part most vulnerable to herbivore attack and the most valued organ. We concluded that EFNs of S. adstringens are anti‐herbivore defenses whose pattern matches the predictions of the optimal defense hypothesis.     

Distribution and structural aspects of extrafloral nectaries in Cedrela fissilis (Meliaceae)

The occurrence of extrafloral nectaries (EFNs) in Meliaceae has been reported for some genera, but little anatomical data are available. Therefore, to determine the distribution and structural aspects of EFNs, Cedrela fissilis Vell. leaves in different stages of development were collected, fixed, and processed for light and scanning electron microscopy. On the petiole, rachis and petiolule, EFNs were found to be arranged predominantly towards the abaxial surface, while their occurrence in leaflet blades was restricted to the abaxial surface of the major veins, noticeably on the midrib. Basal leaflets displayed few EFNs; however, we observed an increase towards the leaf's apex. The leaf can contain more than 300 inconspicuous EFNs, which show secretory activity throughout the leaf's life. Two EFN morphotypes were visible: flattened or elevated, both circular or slightly elliptical and similar in origin and tissue composition. The secretory tissue is embedded in the rachis cortex or in the major veins of the leaf blade and EFNs are not vascularized. The EFN secretory pole shows a uniseriate epidermis with compactly arranged cells and a thin cuticle; stomata and trichomes are absent. The observation of ant visits at these structures reinforces the assumption that EFNs mediate ant–plant interactions and play a protective role against herbivores throughout the life of a leaf.     

Morpho–anatomical and ultrastructural analysis of extrafloral nectaries in Inga edulis (Vell.) Mart. (Leguminosae)

The presence of extrafloral nectaries (EFNs) between leaflets is an usual feature in Inga edulis (Vell.) Mart. (Leguminosae). Extrafloral nectaries are secretory structures involved in production of nectar and which serve in the protection of plants against herbivores through association with ants. This study aimed to characterize the EFNs of I. edulis at different developmental stages and describe their morphology, histochemistry and ultrastructure. Leaf fragments, containing secretory structures, were processed according to standard methods for light, scanning and transmission electron microscopy. The EFNs were classified into three stages based on morphology: pre‐secretory, secretory and post‐secretory. The pre‐secretory stage occurs in young leaves, whereas secretory and post‐secretory stages occur in developed and senescent leaves, respectively. The EFNs possess a concave surface and a central cleft in which nectar is accumulated and which was not observed in pre‐secretory EFNs. Histochemical tests identified the presence of sugars, proteins, phenolic compounds, mucilage and lipids at all developmental stages of the EFNs. Calcium crystals were identified in all tissues and stages of the EFNs. The secretory cells of the EFNs exhibit a granular cytoplasm, small vacuoles, prominent nuclei, smooth endoplasmic reticulum and mitochondria. Post‐secretory stage EFNs exhibited intense cytoplasmic degradation and the presence of microorganisms. The performance of EFNs of I. edulis appear to follow the leaf development.     

Anatomy of the extrafloral nectaries in species of Chamaecrista section Absus subsection Baseophyllum (Leguminosae,Caesalpinioideae)

In this paper the ontogenesis and histochemistry of the petiolar glands found on the petiole/rachis of the eight Chamaecrista species of the section Absus, subsection Baseophyllum (Leguminosae, Caesalpinioideae) are studied by using light microscopy techniques, aiming to characterise these structures and to provide taxonomic characters which may be useful in phylogenetic approaches. Strips for glucose identification reacted positively with the exudates of the glands, confirming the presence of nectar in the secretion, characterising these glands as extrafloral nectaries (EFN). Histochemical tests also detected the presence of neutral and acid muco-polysaccharides, pectins, mucilages, total proteins, and phenolic compounds in the EFNs. The EFNs arise from a group of meristem cells (protodermis, ground meristem and procambium) in the petiole/rachis. All EFNs of the investigated taxa share some morpho-anatomical characters, so that their peculiarities are too weak to be used alone in the identification of particular species. Rather their similarities may be used to include these species into a single group, supporting the hypothesis of monophyly of the subsection Baseophyllum.     

Morphological characterization of extrafloral nectaries and associated ants in tropical vegetation of Los Tuxtlas,Mexico

Extrafloral nectaries (EFNs) are glands that produce sugary exudates and can be located in any vegetative or reproductive structure of the plant. The EFNs occur in different locations on the leaves, stems, inflorescences and flowers (but are not directly involved with pollination). Occurrence of EFNs on plants of coastal vegetation, tropical rain forest and cloud forest in southern Mexico was studied within Los Tuxtlas Biosphere Reserve, Veracruz. We focused on determining the identity and species richness of plants with EFNs, and describing EFNs morphologies. We found 50 species of plants with EFNs (16 families, 31 genera), which corresponds to approximately 5% of the flora reported for the field site (943 species). Trees were the life form with the greatest representation of EFNs while shrubs and epiphytes had the least representation. EFN-bearing plants were particularly well represented in the families Fabaceae, Euphorbiaceae, Convolvulaceae, Bignoniaceae, Malpighiaceae, Passifloraceae, Costaceae, Tiliaceae, while eight other families had only one species. We found six different types of EFNs according to their morphological structure. Dissimilarity analyses between plants and ant species showed that the forest in the Los Tuxtlas region has a rich array of ant species associated with EFNs, with a low niche overlap of ant species. This diversification in ant use of EFNs is of particular interest from an ecological and evolutionary perspective (potential mutualisms with adaptative value), but this deserves still further studies in detail. The present study shall provide basic information for future research in these fields of plant–animal interactions in neotropical vegetation.     

Translucent Glands and Secretory Canals in Hypericum perforatum L. (Hypericaceae): Morphological, Anatomical and Histochemical Studies During the Course of Ontogenesis

Hypericum perforatum L., traditionally used in folk medicineas a therapeutic plant, is today being evaluated for its antidepressantand antiretroviral activities. The species is characterizedby the presence of different types of secretory structure: translucentglands or cavities, black nodules and secretory canals. Theaim of this work was to characterize the translucent glandsand secretory canals in both the floral and vegetative parts,from morphological, anatomical and histochemical points of view.Translucent glands consist of a sub-epidermal cavity delimitedby two layers of cells. There are three types of secretory canal:type A, with a narrow lumen, and types B and C, both with awide lumen, but with different patterns of development. Histochemicaltests showed that all these structures contain alkaloids andlipids but not pectic-like substances and proteins. Tests forresins, essential oils and tannins gave different responsesin different parts of the plant. Copyright 2001 Annals of BotanyCompany Hypericum perforatum, St. John's wort, secretory structures, morphology, anatomy, histochemistry     

Extrafloral nectaries in Philodendron (Araceae): distribution and structure

Extrafloral nectaries (EFNs) are involved in animal–plant interactions that lead to protection against herbivory. The presence of EFNs in Araceae is rare, besides Philodendron, there is report for only two other genera. With the aim to investigate the occurrence of EFNs in Philodendron and to describe the distribution patterns and structural organization of these glands, 75 Philodendron spp. were examined, 16 of which were selected for study by light microscopy. Three Homalomena spp. were also examined for EFNs, but these were not found. Philodendron martianum was employed as a model for additional study using scanning and transmission electron microscopy. The studied EFNs showed a high degree of structural similarity. They were present in the prophyll, leaf and spathe, becoming functional in young organs. In surface view, EFNs consisted of small areas and showed one or more stomata through which secretions were released. The secretory cells formed a globular region surrounded by ground parenchyma. In P. martianum, nectariferous parenchyma cells exhibited typical features of cells with high metabolism related to nectar secretion. These results allow us to infer that EFNs have a widespread occurrence in Philodendron, and they remain an exclusive character for this group. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2016, 180 , 229–240.     

Progress in mechanism of salt excretion in recretohalopytes

The recretohalophyte with specialized salt-secreting structures including salt glands and salt bladders can secrete salt from their bodies and easily adapt themselves to many kinds of salt habitats. Salt glands and salt bladders, arose from dermatogen cells, are excretory organs specially adapted for dealing with ionic homeostasis in the cells of recretohalophytes. The main function of salt glands or salt bladders is to secrete excess ions that invade the plant. The structures of salt glands or salt bladders differ among plant species. In addition to structural differences, salt glands also differ in their secretion abilities. In this review, we mainly focus on recent progress in the mechanism of salt excretion of salt glands and salt bladders, and in particular, emphasize the vesicle-mediated secretion systems from the vacuole to the plasmalemma and the possibly involved membrane-bound translocating proteins for salt secretion of plant gland secretory cell.     

Anatomy of extrafloral nectaries in Fabaceae from dry‐seasonal forest in Brazil

Extrafloral nectaries (EFNs) are found in many species of Fabaceae. The aim of this work is to describe the internal morphology of the EFNs from species of Fabaceae found in areas of dry‐seasonal forest in north‐eastern Brazil. All species of Fabaceae with EFNs found were collected and samples were submitted to conventional techniques for anatomical and scanning electronic microscopy analysis. EFNs were found in 35 species, of which 32 were examined anatomically. All types have epidermal cells, secretory tissues and vascular bundles in the EFNs. Sclerenchymatous cells were found between the secretory tissues and the vascular tissues, with a few exceptions. The function of these cells is not clear; however, a role in the transportation of the sap in the nectary or with the support of the secretory tissue is possible. The nectar is released through glandular trichomes, secretory pores or even by breaking the epidermal cells and cuticle. The internal patterns found in the EFNs from different species and genera can provide important information for taxonomic and evolutionary studies in the family. © 2010 The Linnean Society of London, Botanical Journal of the Linnean Society, 2010, 163 , 87–98.     

Morphology and development of secretory structures in Hypericum perforatum and H. richeri

Secretory organs are a specialised anatomical feature of plants, these tissues function in the production and/or storage of specific chemical substances, which often have pharmacological properties. The genus Hypericum is characterised by the presence of specialised secretory structures such as black nodules, translucent glands and secretory canals. The presence of these structures is not homogeneous for all the species or between the various floral and vegetative parts of the plants. In this study, we have compared the distributions, morphology and development of secretory structures in the leaves of H. perforatum and H. richeri. Whilst, black nodules occurred in both species, translucent glands followed different development stages depending on the leaf age.     

Anatomical and chemical analyses of leaf secretory cavities of Rustia formosa (Rubiaceae)

Foliar secretory cavities, commonly called leaf pellucid glands, have been reported in many families of vascular plants. In the Rubiaceae, these structures have only been found in the sister genera Rustia and Tresanthera, which are also anomalous within the family because they have poricidal anthers, and in the distantly related Heterophyllaea. General leaf anatomy, with particular attention to secretory cavities, as well as the chemical analysis of the secreted substances of Rustia formosa, is presented here for the first time. The secretory structures have been found in the lamina between the palisade and spongy parenchymas and in the cortical region of the petiole. The chemical analysis showed that the essential oil secreted is a complex mixture of at least 75 components, mostly of sesquiterpenoid composition. Illustrations of the leaf anatomy, details of the secretory structures of Rustia formosa, a gas chromatogram, and a table of the principal components of the leaf essential oil are included.     

Distribution, structural and ecological aspects of the unusual leaf nectaries of Calolisianthus species (Gentianaceae)

Nectaries in leaves of Gentianaceae have been poorly studied. The present study aims to describe the distribution, anatomy, and ecological aspects of extrafloral nectaries (EFNs) of three Calolisianthus species and in particular the ultrastructure of EFNs in Calolisianthus speciosus during leaf development, discussing its unusual structure. Leaves of Calolisianthus species were fixed and processed by the usual methods for studies using light, scanning microscopy and transmission electron microscopy (TEM). Ion chromatography was used to analyze the nectar exudates of C. speciosus. The distribution patterns of nectar secretion units were analysed by ANOVA and t-tests. Two EFNs that can be seen macroscopically were observed at the bases of C. speciosus and C. pendulus leaves. Such large nectaries are absent there in C. amplissimus. Another similarly large EFN is observed at the apex of each leaf in all species. The EFNs at the base of the young leaves in C. speciosus are visited by ants during the rainy season. EFNs are formed by several nectar secretory units (nectarioles) that are present throughout the leaves. Each nectariole is formed by rosette cells with a central channel from which the nectar is released. Channels of old C. speciosus and C. pendulus EFNs were obstructed by fungi. TEM of EFNs in young leaves showed cytoplasms with secretion, small vacuoles, mitochondria, cell wall ingrowth, and plasmodesmata. TEM of EFNs in old leaves demonstrated dictyosomes, plastids, mitochondria, segments of endoplasmatic reticulum, and lipid droplets. The nectar contains sucrose, glucose and fructose.     

Evolution of extrafloral nectaries: adaptive process and selective regime changes from forest to savanna

Much effort has been devoted to understanding the function of extrafloral nectaries (EFNs) for ant–plant–herbivore interactions. However, the pattern of evolution of such structures throughout the history of plant lineages remains unexplored. In this study, we used empirical knowledge on plant defences mediated by ants as a theoretical framework to test specific hypotheses about the adaptive role of EFNs during plant evolution. Emphasis was given to different processes (neutral or adaptive) and factors (habitat change and trade‐offs with new trichomes) that may have affected the evolution of ant–plant associations. We measured seven EFN quantitative traits in all 105 species included in a well‐supported phylogeny of the tribe Bignonieae (Bignoniaceae) and collected field data on ant–EFN interactions in 32 species. We identified a positive association between ant visitation (a surrogate of ant guarding) and the abundance of EFNs in vegetative plant parts and rejected the hypothesis of phylogenetic conservatism of EFNs, with most traits presenting K‐values < 1. Modelling the evolution of EFN traits using maximum likelihood approaches further suggested adaptive evolution, with static‐optimum models showing a better fit than purely drift models. In addition, the abundance of EFNs was associated with habitat shifts (with a decrease in the abundance of EFNs from forest to savannas), and a potential trade‐off was detected between the abundance of EFNs and estipitate glandular trichomes (i.e. trichomes with sticky secretion). These evolutionary associations suggest divergent selection between species as well as explains K‐values < 1. Experimental studies with multiple lineages of forest and savanna taxa may improve our understanding of the role of nectaries in plants. Overall, our results suggest that the evolution of EFNs was likely associated with the adaptive process which probably played an important role in the diversification of this plant group.     

Extrafloral nectaries of four varieties of <Emphasis Type="Italic">Chamaecrista ramosa</Emphasis> (Vogel) H.S.Irwin &amp; Barneby (Fabaceae): anatomy,chemical nature,mechanisms of nectar secretion,and elimination

Considering the importance of extrafloral nectaries (EFNs) in Fabaceae, the objectives of this research were to analyze (1) the anatomical and histochemical characteristics of the EFNs of Chamaecrista ramosa var. ramosa, C. ramosa var. curvifoliola, C. ramosa var. parvifoliola, and C. ramosa var. lucida and (2) the ultrastructure of the EFNs of C. ramosa var. ramosa. Standard techniques in plant anatomy and transmission electron microscopy were used. The anatomical analyses confirmed the characteristics described for extrafloral nectaries, evidencing three well-defined regions: epidermis, nectariferous, and subnectariferous parenchymas. Carbohydrates, proteins, pectins/mucilages, and lipids were detected by histochemical analyzes in all varieties. The ultrastructure of the EFNs of C. ramosa var. ramosa allowed the observation of microchannels at the external periclinal cell walls of the epidermis covering the secretory region. The nectariferous and subnectariferous parenchyma cells have periplasmic spaces, large plastids containing starch grains and plastoglobules, mitochondria, developed endoplasmic reticulum, large vacuoles with electron-dense contents, and membrane residues may be associated with the vacuole, suggesting the occurrence of autophagic processes. The anatomical, histochemical, and ultrastructural patterns revealed characteristics that confirm the glands of C. ramosa as extrafloral nectaries and suggest the eccrine mechanism of secretion.     

Anti-herbivory defense of two <Emphasis Type="Italic">Vicia</Emphasis> species with and without extrafloral nectaries

The effects of direct and indirect defenses differ among plant species, and the variation in the mode of plant defenses might reflect physiological and/or ecological constraints of each mode of defense related to the growth and reproduction of individual plant species. To evaluate the advantages and disadvantages of indirect ant-mediated defense via extrafloral nectaries (EFNs), we compared the herbivory pressure, leaf chemicals, vegetative growth, and reproduction between two species of vetches, Vicia sativa var. angustifolia (Reichard) Wahlenb (Leguminosae) with EFNs and V. hirsuta (L.) SF Gray without EFNs (or with very small EFNs). Indirect ant defense of V. sativa was not consistently reliable because of the low constancy of ant attraction. In addition, V. sativa was more vulnerable to attack by herbivores than V. hirsuta. The estimated total amount of sugars secreted by EFNs of V. sativa corresponded to 0.5% of total leaf biomass, and 0.07% of total plant biomass, indicating a low investment to the production of extrafloral nectar. Vicia sativa plants grew more rapidly than V. hirsuta plants during the reproductive stage. Therefore, we consider that V. sativa adopts the ant defense via EFNs in spite of its low reliability because the indirect ant defense supported by EFNs requires only low investment, allowing the plants to attain rapid growth in the early spring.     

The uncommon cavitated secretory trichomes in Bauhinia s.s. (Fabaceae): the same roles in different organs

Cavitated secretory trichomes are characterized by a short or absent stalk that is connected to a secretory hollow head. They are rare structures in angiosperms; in Fabaceae, they have been recorded in only seven genera, including Bauhinia s.s. Because B. curvula and B. rufa exhibit glands that are responsible for attracting pollinators to flowers, this study aimed to test whether the cavitated secretory trichomes present in the flowers of these species have an attraction function. As leaf trichomes are commonly related to plant defence, comparative analyses of the morphology, ontogeny, ultrastructure and chemical profile of the secretory trichomes present in flowers and leaves were conducted. It was found that cavitated secretory trichomes are similar in their external morphology and development, regardless of the organ or species analysed. However, interspecific differences were found in the secretion process and chemical profile of the exudate. The differences found in the cavitated secretory trichomes between species indicate that they secrete distinct compounds, whereas the similarities found in these structures between vegetative and reproductive organs indicate that the cavitated trichomes have equivalent ecological functions within a species, probably in plant defence during organ development. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2016, 180 , 104–122.     

The ontogeny of plant indirect defenses

Plants frequently attract natural enemies of their herbivores, resulting in a reduction in tissue damage and often in enhanced plant fitness. While such indirect defenses can dramatically change as plants develop, only recently have ecologists begun to explore such changes and evaluate their role in mediating plant–herbivore–natural enemy interactions. Here we review the literature documenting ontogenetic patterns in plant rewards (i.e. extrafloral nectaries (EFNs), food bodies (FBs) and domatia) and volatile organic compounds (VOCs), and identify links between ontogenetic patterns in such traits and the attraction of natural enemies (ants). In the case of reward traits we concentrate in ant–plant studies, which are the most numerous. We report that all indirect defensive traits commonly vary with plant age but ontogenetic trajectories differ among them. Myrmecophytic species, which provide both food and shelter to their defenders, do not produce rewarding traits until a minimum size is reached. Then, a pronounced increase in the abundance of food rewards and domatia often occurs as plants develop, which explains the temporal succession or colony size increase of mutualistic ant species and, in some cases, leads to a reduction in herbivore damage and enhanced fitness as plants age. In contrast, ontogenetic patterns were less consistent in plant species that rely on VOC emissions to attract natural enemies or those that provide only food rewards (EFNs) but not nesting sites to their associated ants, showing an overall decline or lack of trend with plant development, respectively. Future research should focus on uncovering: (i) the costs and mechanisms underlying ontogenetic variation in indirect defenses, (ii) the relative importance of environmental and genetic components shaping these ontogenetic trajectories, and (iii) the consequences of these ontogenetic trajectories on plant fitness. Advances in this area will shed light on the context dependency of bottom-up and top-down controls of herbivore populations and on how natural selection actually shapes the ontogenetic trajectories of these traits.     

家蚕性附腺发育与核酸及利它素蛋白变化的关系

对不同发育时期家蚕Bombyx mori雌性性附腺核酸和蛋白质含量测定的结果表明, 从家蚕化蛹后第6天到成虫羽化当天的性附腺内总蛋白质含量不断增加,至羽化当天为最高,达860±70 μg/对。不同时期内能引诱野蚕黑卵蜂识别寄主的利它素在总蛋白中所占的比例差异明显,从化蛹后第6天的10%增加到羽化后的58%。性附腺的总RNA含量从化蛹第6天到成虫羽化前1天几乎是直线增加,但羽化后下降很快。不同时期分泌部中总RNA含量变化与贮存部明显不同。含量最高时,分泌部RNA可占整个性附腺RNA的90%以上,而贮存部总RNA含量则远少于分泌部,羽化当天约为分泌部的十分之一。分泌部总RNA中的18S亚基含量远高于28S亚基,明显不同于贮存部的。从分泌部总RNA中分离的mRNA存在明显的条带分布,这预示着高丰度的mRNA的存在与总蛋白中高含量利它素的存在有着特殊对应关系。