1,721,040 research outputs found
Beyond nectar sweetness: the hidden ecological role of non-protein amino acids
No full text1) Studies from the last decade clearly demonstrate that nectar is much more than just a simple alimentary reward for pollinators. Considerable progress has been made in recent years with regard to the chemical ecology of nectar, demonstrating unequivocally that its chemistry is strongly involved in the interactions between plants and a larger variety of organisms - from bacteria to fungi and animals- than previously thought. As far as plant-pollinator relationships are concerned, attention has recently been directed towards secondary compounds, mainly alkaloids that are able to induce a wide range of behavioural and physiological responses in floral visitors. Nonetheless the study of some other secondary compounds, such as non-protein amino acids (NPAAs), has been neglected. The roles of these substances in nectar are still unknown although several ecological and physiological functions have been attributed to a number of NAAs in both animals and plants in several ecological and physiological contexts.
2) The existence of NPAAs in floral nectar was first reported in early surveys of nectar composition dating from the 1970s. Since that time, only a very few papers have mentioned the presence of these compounds in nectar, but without any hypothesis relating to their ecological role and their putative effect on flower visitors. This appears surprising considering that interaction with other organisms is a recognized function of NPAAs in plants.
3) Here, after exploring the multiple roles of NPAAs at the community level and focusing on the more recent advances in nectar chemistry and ecology, I review the small body of literature relating to the presence of NPAAs in nectar before outlining some ecological roles in the light of complex, nectar-mediated, plant-animal interactions that have been recognized recently for other nectar secondary compounds based also on data and information obtained for other biological systems (from arthropods to humans).
4) Synthesis. By integrating data obtained from both literature and field observations, I have arrived at the proposal that non-protein amino acids in nectar may contribute to the plant-insect network of interactions in a number of ways: by affecting the physiology of the nervous system of the insect, regulating nectar intake through phagostimulation and promoting muscle function during flight. Confirmation of these hypotheses are needed in order to reinforce the concept that plants are able to affect the foraging behaviour of insects through nectar chemistry, thereby eventually optimizing their pollination effectiveness
Effect of pistil age on pollen tube growth, fruit development and seed set in Cucurbita pepo L.
No full textThe effects of pistil age on pollen tube growth, fruit development and seed set were studied in Cucurbita pepo L., the flower of which opens for only six hours. Stigma receptivity lasts four days, from one day before until two days after anthesis. Style receptivity lasts three days, from the day before to the day after anthesis. Ovule receptivity lasts two days: the day of anthesis and the day before. The rate of pollen tube growth varies in different parts of the pistil and in relation to pistil age. In the stigmatic and stylar region, the tubes grow faster if pollination occurs the day before anthesis; in the ovary they grow faster when pollination occurs at anthesis. In the receptacle region, where the transmitting tissue is reduced, the growth rate decreases independently of the time of pollination. The fruits are larger and heavier with more seeds when pollination occurs at anthesis. There is a positive correlation between seed number and fruit weight when pollination occurred at anthesis and the day before
Nectar resorption and translocation in Cucurbita pepo L. and Platanthera chlorantha Custer (Rchb.)
No full textNectar resorption and sugar translocation were studied in Cucurbita pepo (Cucurbitaceae) and Platanthera chlorantha
(Orchidaceae) by micro-autoradiography. In both species, nectar
was resorbed in pollinated and unpollinated flowers and ovules developing into seeds were found to be the main sugar sink. In C. pepo, the mobility of resorbed sugars in pollinated female flowers was higher than in unpollinated ones; male flowers showed lower mobility of resorbed sugar. In P. chlorantha, radioactivity was detected in pollinated flowers below and above labelled unpollinated ones: the nearer the flower, the stronger the
accumulation of label in developing fruits
Nectar production and presentation
No full textNectar secretion is complicated to study from the ultrastructural point of view because it is a dynamic process involving many tissues simultaneously. Study may also be affected by artefacts created by chemical fixation procedures, although this problem can be overcome by freeze-drying and freeze substitution techniques (Zhu & Hu, 2002; Stpiczyńska et al., 2005b). Previous research has focused on the ultrastructure of secretory cells, especially secreting trichomes (Robards & Stark, 1988), and a general model of nectary function as a whole is still lacking. © 2007 Springer. All rights reserved
Nectary structure and ultrastructure
No full textIt is easy to define nectaries from a functional point of view: they are plantsecreting structures that produce nectar, but it is difficult to provide a general definition. From the anatomical point of view nectaries vary widely in ontogeny, morphology, and structure (Fahn, 1979a, 1988; Durkee, 1983; Smets et al., 2000), both between species and within species, depending on flower sexual expression or flower morph in heterostylous and heteroantheric species (Nepi at al., 1996; Küchmeister et al., 1997; Fahn & Shimony, 2001; Pacini et al., 2003). Intraspecific morphological differences exist between flowers of the same plant and between plants of the same species with different ploidy (Davis et al., 1996), and morphological characters may be nean shrub community was largely shaped by phylogenetic and climate constraints. In the course of the flowering season (spring-summer) stomatal opening and nectary size decreased, thus minimizing nectar flow at a time when water was scarce. They hypothesized that very concentrated nectar was secreted via large modified stomata, whereas cuticular secretion was mainly encountered in species with very thin nectars. Petanidou (2007) speculates that the frequency of species with stomatal nectar secretion should be much higher in hot and arid climates like the Mediterranean and deserts than in temperate ones. © 2007 Springer. All rights reserved
The complexity of nectar: secretion and resorption dynamically regulate nectar features
No full textIn this paper, we review the phenomenon of nectar resorption, focusing on its physiological and ecological meaning. Nectar resorption is a phenomenon that has long been known but was rarely reported until the1990s. It has more recently been demonstrated in several species by various direct and indirect methodologies. It has generally been demonstrated in senescent flowers as a phenomenon separate in time from, and independent of, nectar secretion. The significance of this type of resorption is generally recognized as a resource-recovery strategy, recycling at least some materials invested in nectar production. Nevertheless, nectar resorption can occur concomitantly with nectar secretion. Nectar production is therefore best considered as a unified process comprising nectar secretion and resorption. The modulation of these two opposite phases allows nectar concentration to be maintained in a range suitable for pollinators (nectar homeostasis). The mechanism of nectar resorption at the cell level has received little attention, and its molecular basis can only be hypothesized on the basis of recent studies concerning sugar sensing. © 2007 Springer-Verlag
Dilute nectar in dry atmosphere: nectar secretion patterns in Aloe castanea (Asphodelaceae)
No full textAloe species commonly flower during the winter dry season in southern Africa and produce abundant dilute nectar. We investigated variability in nectar production and availability in Aloe castanea because evaporation is more likely from its open flowers than from the tubular flowers of most other Aloe species. The greatest variability in nectar production was associated with flower age, and weather conditions and individual plants also had significant effects. However, when unscreened flowers of similar age were sampled throughout a clear day, nectar volumes and concentrations were remarkably constant, and concentrations did not exceed 10% w/w. Variability in concentration could be reduced by reabsorption of sugars, but there was no evidence of reabsorption after addition of relatively concentrated nectar (26.6%) to flowers. It appears that rapid secretion throughout the day accounts for the constant low concentration. © 2005 by The University of Chicago. All rights reserved
Nectaries and male-biased nectar production in protandrous flowers of a perennial umbellifer Angelica sylvestris L. (Apiaceae)
Full text linkNectar is the most common floral pollinator reward. In dichogamous species, floral nectar production rates can differ between sexual phases. We studied the structure of nectaries located on the stylopodium and nectar production in protandrous umbellifer Angelica sylvestris. Our study species produced nectar in both floral sexual phases. Nectar sugar concentration was low (on average 22 ± 11 %, mean ± SD) and the nectar hexose rich and composed of sucrose, glucose, fructose and a small amount of amino acids, including β-alanine, a non-protein amino acid. Although nectar composition and sugar concentration varied little between floral sexual phases, nectar production showed a threefold reduction during the stigma receptive period. This is in contrast to other studies of Apiaceae that have reported female-biased nectar production, but in the direction predicted by plant sexual selection theory, suggesting that in pollen-unlimited species, floral rewards mainly enhance male reproductive success. The structure of the nectary was similar at the two sexual stages investigated, and composed of a secretory epidermis and several layers of nectariferous and subsecretory parenchyma. The nectary cells were small, had large nuclei, numerous small vacuoles and dense, intensely staining cytoplasm with abundant endoplasmic reticulum, mitochondria and secretory vesicles. They contained abundant resin-like material that may potentially act as defence against microbes. Starch was rarely observed in the nectary cells, occurring predominantly at the female stage and mainly in guard and parenchyma cells in close proximity to stomata, and in subsecretory parenchyma. The main route of nectar release in A. sylvestris seems to be via modified stomata
Nectar resorption and pollination economy
No full textThe nectaries and nectar of three species (Helleborus bocconei, Cucurbita pepo and Linaria vulgaris) that differ in ecological, cytological and physiological characteristics are compared. Nectar is resorbed in Cucurbita pepo and Linaria vulgaris, but in different ways and at different rates. Nectar secretion and resorption, if any, are discussed in terms of the economics of the plant and environmental conditions
Nectar biodiversity: a short review
No full textNectaries differ in many aspects but a common feature is some kind of advantage for the plant conferred by foraging of consumers which may defend the plant from predators in the case of extrafloral nectaries, or be agents of pollination in the case of floral nectaries. This minireview is concerned mainly with floral nectaries and examines the following characteristics: position in flower; nectary structure; origin of carbohydrates, aminoacids and proteins; manner of exposure of nectar; site of nectar presentation; volume and production of nectar in time; sexual expression of flower and nectary morphology; nectar composition and floral sexual expression; variability of nectar composition; fate of nectar; energy cost of nectar production. The species of certain large families, such as Brassicaceae, Lamiaceae and Asteraceae, resemble each other in nectary organisation; other families, such as Cucurbitaceae and Ranunculaceae, have various types of organisation. A scheme is presented to illustrate factors influencing nectary and nectar biodiversity
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