Class Of Secondary Compounds Research Articles

Ecdysteroids

Ecdysteroid: member of a class of polyhydroxylated steroids found in invertebrate animals (zooecdysteroids; moulting hormones), plants (phytoecdysteroids) and fungi (mycoecdysteroids). Over 500 structural analogues are currently known. Biosynthetically, they derive from C27-, C28- or C29-sterols. The most frequently encountered analogue (in arthropods and plants) is 20-hydroxyecdysone (2β,3β,14α,20R,22R,25-hexahydroxycholest-7-en-6-one). In arthropods, ecdysteroids occur universally and regulate development by inducing moulting and reproduction, where their action is mediated by high-affinity binding to an intracellular member of the class of nuclear receptor (NR) proteins (ecdysteroid receptor; EcR) dimerised with a second NR (USP/RxR). This receptor complex binds to specific DNA promoter sites and regulates gene expression. In plants, ecdysteroids are a class of secondary compounds, occurring in varying amounts in certain species, but not all in others. Phytoecdysteroids are believed to contribute to the reduction of invertebrate predation by acting as feeding deterrents or endocrine disruptors. Ecdysteroids also possess a wide range of positive pharmacological effects in mammals, where the mode of action involves moderate-affinity binding to plasma-membrane-bound receptors and not interaction with the classical NRs for vertebrate steroid hormones.

Physicochemical profile of the oil from the seed of Tontelea micrantha (Celastraceae)

The oil from the seed of Tontelea micrantha is utilized in traditional medicine as a topical antiseptic and as an anti-inflammatory for the treatment of respiratory diseases. The dynamic of the oil secretion in seed tissues was analyzed by transmission electron microscopy, classes of secondary compounds were identified by histochemical and phytochemical tests, the quality of the oil was determined by physical and chemical analysis, the fatty acid profile was obtained, and the volatile compounds were extracted by headspace method and identified by gas chromatography coupled to a mass spectrometer. The oil production takes place during the final stages of seed maturation, and large vacuoles are involved in its secretion and accumulation. Flavonoids, tannins and alkaloids, linoleic and oleic acids, α-pinene and junipene are present in the oil. Several of these compounds are known to have biological activity and may support the traditional medicinal use of the species.

Effects of endophytic and saprophytic fungi on in vitro methanogenesis

The predominance of pasture in the diet of ruminants in New Zealand presents specific challenges for mitigation of enteric methane emissions. However, there is preliminary evidence from both laboratory and animal-based studies that some fungi may suppress enteric methanogenesis. This study determined the antimethanogenic potential of a range of endophytic (Neotyphodium species) and saprophytic (Geotrichum, Monascus, Mortierella and Penicillium species) fungi. Candidate fungi were selected on the basis of their production of various classes of secondary compounds and screened in an in vitro batch-culture fermentation assay. No strains of endophyte in ryegrass or tall fescue suppressed methanogenesis compared with their endophyte-free controls. The supernatant fractions from three strains of Mortierella wolfii were the most promising fungi identified. They suppressed methanogenesis as effectively as an inhibitor of methanogenesis (bromoethane sulphonate at 30 µmoles/L), without also reducing overall fermentation. These strains should be investigated further by screening fresh cultures grown under contrasting conditions to establish some variation in putative bioactive compounds.

Herbivore-deterring secondary compounds in heterophyllous woody species of the Mascarene Islands

Heterophylly (juvenile-adult leaf dimorphism) is widespread among native woody species of the Mascarene Islands, but the causes to this phenomenon have so far not been fully explained. The absence of mammals and dominance of now extinct giant tortoises and flightless birds are characteristics of the original Mascarene fauna. The present study investigates the hypothesis that the distinct morphology and colouration of juvenile leaves signalled unpalatability to browsing giant tortoises or birds. Juvenile and adult leaves of 28 heterophyllous woody species endemic to the islands of Mauritius and Rodrigues were screened for possible chemical defences against herbivory. The screening comprised the following classes of secondary compounds: alkaloids, cyanogenic constituents, saponins, simple phenolics, tannins and anthocyanins. The screening showed that there are no consistent significant differences between juvenile and adult leaves regarding any of the studied secondary compound classes, with the exception of the level of anthocyanins, which was significantly higher in juvenile leaves. This difference was also clearly reflected in a generally high degree of red patterning of juvenile leaves. Based on comparisons with floras of other oceanic islands once inhabited by tortoises and birds, and an evaluation of feeding habits of these herbivores, we suggest that the reduced lamina and partly red colouration of juvenile leaves may be an evolutionary response to selective herbivory by birds.

Performance of Colorado potato beetle larvae,Leptinotarsa decemlineata (Say), reared on synthetic diets supplemented withSolanum glycoalkaloids

Glycoalkaloids are a class of secondary compounds (nitrogenous, steroidal glycosides), ubiquitously distributed throughout the Solanaceae. Numerous studies (in planta) have shown that certain glycoalkaloids, e.g., α-tomatine, solanocardenine, and leptine, have a negative impact on performance of the Colorado potato beetle,Leptinotarsa decemlineata (Say). However, the presence of other secondary compounds, as well as the nutritional status of the plants used, are additional variables in such experiments. By rearing Colorado potato beetle, from egg to prepupal stage, on a synthetic diet supplemented with the glycoalkaloids α-tomatine, α-chaconine, α-solanine, leptine I and the steroidal aglycone solanidine, we have been able to further establish the effects (ex planta) of these compounds on the Colorado potato beetle. Leptine I displayed a dose-dependent negative activity against the Colorado potato beetle (as measured by larval weight gain and tune to molt), when assayed at 0.31, 0.62 and 1.23 mM concentrations; however, by the fourth stadium no effect was found. When Colorado potato beetle were fed a higher concentration of leptine I (2.4 mM), there was a sustained effect in all stadia. At 2.4 mM, leptine I displayed a greater negative impact on Colorado potato beetle growth and development than did α-tomatine. α-Chaconine at 2.4 mM did not impair Colorado potato beetle performance relative to Colorado potato beetle reared on control diets. α-Chaconine plus α-solanine, at concentrations commonly found inSolanum tuberosum L. foliage (0.6 and 0.3 mM respectively), did not impair Colorado potato beetle performance. The steroidal aglycone solanidine (2.4 mM) had a significant negative impact on Colorado potato beetle performance. Results are discussed in the context of host-plant resistance and insect-plant interactions.

Biosynthetic origin of carbon-based secondary compounds: cause of variable responses of woody plants to fertilization?

We propose that variation in the responses of carbon-based secondary compounds to fertilization in woody plants has a biosynthetic cause. The synthesis of phenylpropanoids and derived compounds (e.g., condensed tannins) competes directly with the synthesis of proteins, and therefore with plant growth, because of a common precursor, phenylalanine. In contrast, the biosynthesis of terpenoids and of hydrolyzable tannins proceeds presumably without direct competition with protein synthesis. Therefore, accelerated plant growth induced by fertilization may cause a reduction in concentrations of phenylpropanoids but may affect less or not at all the levels of other classes of secondary compounds. A meta-analysis based on fertilization experiments with 35 woody plant species supported the predicted differences fertilizing significantly decreased concentrations of phenylpropanoids but not of terpenoids or hydrolyzable tannins.

Predation, herbivory, and kelp evolution

We propose that the kelps (Laminariales) radiated in the North Pacific following the onset of late Cenozoic polar cooling. The evidence is that (1) extant kelps occur exclusively in cold-water habitats; (2) all but one of 27 kelp genera occur in the North Pacific, 19 of these exclusively; and (3) limpets and herbivorous marine mammals obligately associated with kelps or other stipitate brown algae appeared late in the Cenozoic, even though more generalized forms of both groups are much older. We propose, further, that sea otters and perhaps other groups of benthic-feeding predatory mammals, whose late Cenozoic distributions all were limited to the North Pacific, created an environment for the evolution of kelps in which the intensity of herbivory was unusually low. We hypothesize that this interaction created predictable differences among habitats in the intensity of herbivory on several spatial scales, with resulting trade-offs between anti-herbivore defenses and plant competitive abilities in their respective floras. Sea otters incur time and energy costs for diving, resulting in depth-related reductions to foraging efficiency and thus increased sizes and densities of herbivorous sea urchins. Thus, the deep-water flora is well defended, but competitively subordinate, compared with the shallow-water flora. Similarly, we argue that during the same period of earth history, predation had less of a limiting influence on herbivorous invertebrates in the temperate southwestern Pacific. We hypothesize that (1) consequent biogeographical differences in the intensity of herbivory may have selected the phenolic-rich brown algal flora in temperate Australia/New Zealand; and (2) tightly coevolved plant/herbivore interactions may explain why Australian and New Zealand herbivores are undeterred by phenolics and why other classes of secondary compounds in the Australian/New Zealand flora significantly deter herbivores.

Anti-predation strategies in pteridophytes—a biochemical approach

SynopsisSince they first evolved, pteridophytes have been subjected to attack by micro-organisms and arthropods. Present-day ferns are associated with a complex array of, not only phytophagous, scavenging, predatory and parasitic arthropod species but also fungi, bacteria, viruses and herbivorous mammals.Recent research has tended to stress the importance of secondary plant chemistry in deterring feeding by herbivores and attack by pathogens. Although ferns have a more limited chemical repertoire than the angiosperms, many of the classes of secondary compounds isolated from ferns have been shown to have anti-microbial and anti-herbivore activity under both laboratory and field conditions. Quantitative and qualitative levels are not constant and show great seasonal variation. This chemical variation is important in determining the seasonal patterning of insects and fungi on ferns. New chemical techniques are increasing our knowledge of the biosynthesis and chemical structures of these ecologically important compounds.Flowering plants show both constitutive and induced resistance as a consequence of herbivore attack. A search for short-term induced chemical responses in ferns have so far yielded negative results in terms of phytoalexin synthesis or direct chemical response to herbivory.

Defensive Ecology of the Cruciferae

The glucosinolates (mustard oil glucosides), present in all crucifer species examined, seem to provide a major line of chemical defense against bacteria, fungi, insects, and mammals. Circumstantial evidence suggests that other classes of secondary compounds, each restricted to one or a few genera, represent a second line of chemical defense. Survival of wild crucifers depends partly on escape from adapted enemies in time and space. Discovery of crucifers by several enemy species is aided by behavioral responses to glucosinolates or their breakdown products. Allylglucosinolate (sinigrin) in the leaves of Thlaspi arvense releases allylthiocyanate instead of the more typical allylisothiocyanate, which is used as a host-finding attractant by several insect species. This change in secondary chemistry may reduce the rate of discovery of Thlaspi plants by crucifer-adapted enemies. The defensive ecology of crucifers seems to typify that of herbaceous plants generally: chemical resistance, in the form of small amounts of toxic compounds, combined with low apparency to enemies which are adapted to the chemical defenses. The importance of the Cruciferae and other families of herbaceous plants as sources of food-plants for man may result in large part from their relatively low concentrations of toxins. The mature foliage of trees, shrubs, and grasses, by contrast, remains poor food for man, just as for other plant