Role Of Secondary Metabolites Research Articles

Role of secondary metabolites and pigments in the epidermal tissues, ripe ovaries, viscera, gut contents and diet of the sea cucumber Holothuria atra

The epidermal tissues, ovaries, viscera, gut contents, and the diet of Holothuria atra (Jaeger), collected from the Great Barrier Reef (GBR), Australia, just prior to spawning, contained carotenoid pigments, mycosporine-like amino acids (MAAs) and three other metabolites in varying proportions. Mycosporine-glycine (mycosporine-gly), palythine, asterina-330, shinorine, mycosporine-2-gly, porphyra-334, and palythinol were present in the epidermal tissues. Mycosporine-gly was the major MAA in the epidermal tissues, gut contents and the diet, and the only MAA present in the ripe ovaries and the viscera. Gadusol, a metabolite with antioxidant properties, which co-occurs with MAAs, and in certain instances with trace amounts of 6-deoxygadusol in unfertilised and fertilised eggs and developing larvae of some marine invertebrates and vertebrates, was absent from H. atra. However, 6-deoxygadusol, with similar physical and chemical properties to gadusol, and the proposed biosynthetic precursor of MAAs, was present, but only in the ovaries. This is first report of the presence of this proposed biogenetic precursor of MAAs in significant amounts in a marine invertebrate. Approximately 90% of the total carotenoids of the epidermal tissues, ovaries and viscera of H. atra are highly oxidised, the main component being astaxanthin followed by canthaxanthin. These were the major carotenoids present in the ovaries and the total carotenoid content was highest in the ovaries. β-carotene, a common egg carotenoid, was present in trace quantities in the ovaries but, along with the xanthophylls lutein and zeaxanthin, it occurred in significant amounts in the gut contents and the diet of H. atra. Carotenoid patterns in the epidermal tissues and viscera were strikingly similar, containing β-carotene, canthaxanthin, astaxanthin, zeaxanthin, lutein, phoenicoxanthin and echinenone. The alkaloids homarine and isomeric trigonelline, (structurally unrelated to MAAs) and 6-deoxygadusol were present only in the ovaries and the viscera. It is suggested that these metabolites and pigments are either involved with photoprotection or reproduction, or associated with both processes. The origin, biogenetic relationships and the roles of these metabolites and pigments in H. atra are discussed.

A Review of the Chemical Ecology of Antarctic Marine Invertebrates

The interdisciplinary field of marine invertebrate chemical ecology is relatively young, and particularly so in polar marine environments. In this review we present evidence that the incidence of chemical defense in antarctic benthic marine invertebrate phyla is widespread. Mechanisms of chemical defense have been detected in antarctic representatives of the Porifera, Cnidaria, Brachiopoda, Tunicata, Nemertea, Mollusca and Echinodermata. This argues against earlier bio-geographic theories that predicted a low incidence of chemical defense in polar waters where levels of fish predation are low. Selection for chemical defense in benthic sessile and sluggish marine invertebrates is likely a response to an environmentally stable community shown to be structured primarily by biotic factors such as predation and competition. Holoplankton and the eggs, embryos and larvae of both benthic and planktonic antarctic macroinvertebrates may also employ chemical defense to offset mortality during characteristically slow development and long life span where susceptibility to predation is seemingly high. While most research to date has focused on the role of secondary metabolites in mediating predation, it is likely that bioactive compounds in antarctic marine invertebrates also serve roles as antifoulants and allelochemics. The diversity of bioactive metabolites detected to date in antarctic marine invertebrates sets the stage both for continuing and for broadening efforts to evaluate their functional and ecological significance.

ANTIFUNGAL ACTIVITY OFSOLANUMFRUIT GLYCOALKALOIDS: IMPLICATIONS FOR FRUGIVORY AND SEED DISPERSAL

We tested two sets of hypotheses about the role of secondary metabolites (glycoalkaloids) in ripe Solanum (Solanaceae) fruit. The Directed Toxicity Hypothesis states that these compounds are most toxic to frugivores that do not disperse seeds (e.g., fungi), whereas its alternative, the General Toxicity Hypothesis, states that they are generally toxic to all frugivores. The Removal Rate Hypothesis states that highly rewarding fruits, which are removed rapidly by dispersers, require only low levels of glycoalkaloids for protection against insects and microbes. The alternative Nutrient–Toxin Titration hypothesis states that highly rewarding fruits may be able to maintain higher levels of glycoalkaloids because high nutrient content may offset the negative effects of glycoalkaloids on dispersers. Our previous work with vertebrate frugivores supported the General Toxicity and Removal Rate hypotheses. We used artificial fruit pulp media to measure how the mycelial growth rate of nine fungal species was affected by two glycoalkaloids, α-solasonine and α-solamargine, both common in ripe Solanum fruits. In one set of fungal growth trials, we mimicked two species of fruit, S. americanum with low levels of glycoalkaloid in ripe fruit and S. carolinense with high levels, to determine the relative effects of nutrient and toxin content. In another set of trials, we examined the relative and interactive effects of the two glycoalkaloids. Finally, we tested whether or not increases in nutrient content could offset the negative effects of glycoalkaloids on fungal growth. All fungi tested were inhibited by the glycoalkaloids, with lower levels of antifungal activity for agars corresponding to (low-toxin) S. americanum fruits than to (high-toxin) S. carolinense fruits. Because fungi varied in their degree of inhibition by glycoalkaloids, we found only limited support for the Directed Toxicity Hypothesis. The degree of inhibition for fungi was, on average, similar in magnitude to the negative effects upon vertebrate feeding rates, providing further support for the General Toxicity Hypothesis. Additionally, we found no evidence for differences in antifungal effects between the two glycoalkaloids and no evidence of synergism between them. Nutrient effects were generally small, with little evidence that nutrient variation could compensate for the antifungal activity produced by levels of glycoalkaloids found in ripe S. carolinense fruits. Fruits that are presumably more profitable (S. americanum) are preferred by vertebrate frugivores and contain much lower levels of glycoalkaloid. These results support the Removal Rate Hypothesis. We conclude that glycoalkaloids of Solanum fruits may act as effective antifungal defenses. However, because they are also toxic to seed-dispersing vertebrates, their effects upon fruit–disperser interactions are probably general and important.

Secondary metabolites in plant defence mechanisms.

Many secondary metabolites found in plants have a role in defence against herbivores, pests and pathogens. In this review, a few examples are described and discussed, and some of the problems in determining the precise role(s) of such metabolites highlighted. The role of secondary metabolites in defence may involve deterrence/anti-feedant activity, toxicity or acting as precursors to physical defence systems. Many specialist herbivores and pathogens do not merely circumvent the deterrent or toxic effects of secondary metabolites but actually utilize these compounds as either host recognition cues or nutrients (or both). This is true of both cyanogenic glucosides and glucosinolates, which art discussed in detail as examples of defensive compounds. Their biochemistry is compared and contrasted. An enormous variety of secondary metabolites are derived from shikimic acid or aromatic amino acids, many of which have important roles in defence mechanisms. Several classes of secondary products are 'induced' by infection, wounding or herbivory, and examples of these are given. Genetic variation in the speed and extent of such induction may account, at least in part, for the difference between resistant and susceptible varieties. Both salicylates and jasmonates have been implicated as signals in such responses and in many other physiological processes, though their prescise roles and interactions in signalling and development are not fully understood. Contents Summary 617 I. Introduction 617 II. Cyanogenic glucosides 618 III. Glucosinolates 619 IV. Non-protein amino acids 621 V. Alkaloids 622 VI. Plant phenoiics 623 VII. Plant terpenes, sesquiterpenoids and sterols 626 VIII. Phytoalexins 626 IX. Salicylic acid and methyl jasnionate 627 X. Conclusions 628 References 629.

高等植物における防御機構 植物間競合における二次代謝産物の役割

高等植物における防御機構 植物間競合における二次代謝産物の役割

Role of secondary metabolites in feeding associations between a predatory nudibranch, two grazing nudibranchs, and a bryozoan

The carnivorous nudibranch Roboastra tigris preys preferentially upon two nudibranchs,Tambja abdere and T. eliora, that in turn feed upon the bryozoan Sessibugula translucens. All four organisms contain tambjamines A-D (I-IV) that were shown to be fish feeding inhibitors. When attacked by Roboastra, T. abdere secretes a distasteful mucus containing a total of 3 mg of the tambjamines that sometimes causes the Roboastra to break off the attack. Under similar circumstances T. eliora attempts to swim away; it presumably contains insufficient of the tambjamines to deter Roboastra. Roboastra follows the slime trail of nudibranchs using contact chemoreception and reverses direction when the trail is broken. The slime trail ofT. abdere contains low concentrations of the tambjamines. In Y-maze experiments,T. eliora was attracted towards seawater containing S. translucens and seawater containing 10(-10) M tambjamines A and B (1∶1) but was repelled by seawater containing > 10(-8) M tambjamines A and B. At higher concentrations the mixture of tambjamines may be recognized as an alarm pheromone.

Foreign Body in Nasal Cavity: Removal and Subsequent Rhinoplasty

Numerous species of bacteria use an elegant regulatory mechanism known as quorum sensing to control the expression of specific genes in a cell-density dependent manner. In Gram-negative bacteria, quorum sensing systems function through a cell-to-cell signal molecule (autoinducer) that consists of a homoserine lactone with a fatty acid side chain. Such is the case in the opportunistic human pathogen Pseudomonas aeruginosa, which contains two quorum sensing systems (las and rhl) that operate via the autoinducers, N-(3-oxododecanoyl)-l-homoserine lactone and N-butyryl-l-homoserine lactone. The study of these signal molecules has shown that they bind to and activate transcriptional activator proteins that specifically induce numerous P. aeruginosa virulence genes. We report here that P. aeruginosa produces another signal molecule, 2-heptyl-3-hydroxy-4-quinolone, which has been designated as the Pseudomonas quinolone signal. It was found that this unique cell-to-cell signal controlled the expression of lasB, which encodes for the major virulence factor, LasB elastase. We also show that the synthesis and bioactivity of Pseudomonas quinolone signal were mediated by the P. aeruginosa las and rhl quorum sensing systems, respectively. The demonstration that 2-heptyl-3-hydroxy-4-quinolone can function as an intercellular signal sheds light on the role of secondary metabolites and shows that P. aeruginosa cell-to-cell signaling is not restricted to acyl-homoserine lactones.