Plant secondary chemicals

Jones CG, Firn RD. (1991). On the evolution of plant secondary chemical diversity. The Philosophical Transactions of the Royal Society, 333, 273-80. Despite the overwhelming evidence that most NPs possess no potent, specific biological activity, NP researchers often imply the opposite by using generalisations that imply the opposite. For example, leaf alkaloids... 

Insects are so successful because of their mobility, high reproductive potential, ability to exploit plants as a food resource, and to occupy so many ecological niches. Plants are essentially sessile and can be seen to produce flowers, nector, pollen, and a variety of chemical attractants to induce insect cooperation in cross-pollination. However, in order to reduce the efficiency of insect predation upon them, plants also produce a host of structural, mechanical, and chemical defensive artifices. The most visible chemical defenses are poisons, but certain chemicals, not intrinsically toxic, are targeted to disrupt specific control systems in insects that regulate discrete aspects of insect physiology, biochemistry, and behavior. Hormones and pheromones are unique regulators of insect growth, development, reproduction, diapause, and behavior. Plant secondary chemicals focused on the disruption of insect endocrine and pheromone mediated processes can be visualized as important components of plant defensive mechanisms. 

Many studies of the direct and immediate interactions occurring between plants and insects, as insect predators attempt to feed on plants, have been documented. Thus, research on repellants and antifeedants has received much attention and will not be discussed here. More subtle interactions of plant secondary chemicals inter-ferring with basic insect communication systems have received much... 

Watkins, R.W., Gill, E.L. Cowan, D.P. 1996. Plant secondary chemicals as non-lethal vertebrate repellents. Proc. 17th Vertebrate Pest Conf. (Ed. by R.M. Timm A.C. Crabbs), pp. 186—192. Davis University of California. 

S 111 fi 1 r-reco ve ry p lants Carbon-black plants (furnace process) Primary lead smelters Fuel-conversion plants Sintering plants Secondary metal-production plants Chemical-process plants ... 

Those authors also demonstrated that neither sexual stage nor age of plant had any effect on the qualitative composition of the lipid fractions. They did comment, however, on the possibility that the secondary chemical output of plants at these different sites might reflect local environmental conditions, especially considering that the distance between the sites at Castelluccio and Brucoli is only a few kilometers. They pointed to the work of Howard et al. (1980), who had demonstrated such effects on the chemical content of two species of Laurencia in California over... 

Chemical manipulation of phenolic allelochemical production in plants has two potential values 1) for study of the role of phenolic allelochemicals in plant interactions with other organisms and 2) to alter such interactions for agricultural purposes. The first of these uses has already been accomplished on a limited scale (21, 22, 50, 51, 84, 86), however, there is no published evidence of the latter. This does not mean that herbicide and growth regulator-influences on plant secondary metabolism do not affect agricultural ecosystems by changing allelochemic compositions of plants. It is likely that this is the case, but it... 

Recently, a new polyketide biosynthetic pathway in bacteria that parallels the well studied plant PKSs has been discovered that can assemble small aromatic metabolites.8,9 These type III PKSs10 are members of the chalcone synthase (CHS) and stilbene synthase (STS) family of PKSs previously thought to be restricted to plants.11 The best studied type III PKS is CHS. Physiologically, CHS catalyzes the biosynthesis of 4,2, 4, 6 -tetrahydroxychalcone (chalcone). Moreover, in some organisms CHS works in concert with chalcone reductase (CHR) to produce 4,2 ,4 -trihydroxychalcone (deoxychalcone) (Fig. 12.1). Both natural products constitute plant secondary metabolites that are used as precursors for the biosynthesis of anthocyanin pigments, anti-microbial phytoalexins, and chemical inducers of Rhizobium nodulation genes.12... 

Secondary chemistry differs from primary chemistry principally in its distributional variability and it is this variability that has intrigued ecologists for the past 30 years. Theories [or provisional hypotheses (35)] to account for the structural differentiation and function of secondary metabolites, as well as the differential allocation of energy and materials to defensive chemistry, abound, but they are almost exclusively derived from studies of plant-herbivore interactions (Table 2). This emphasis may be because the function of secondary chemicals in plants is less immediately apparent to humans, who have historically consumed a broad array of plants without ill effects, so alternative explanations of their presence readily come to mind. The fact that animals upon disturbance often squirt, dribble, spray, or otherwise release noxious substances at humans and cause pain leads to readier acceptance of a defensive function [although there are skeptics who are unconvinced of a... 

Cornell HV, Hawkins BA (2003) Herbivore responses to plant secondary compounds a test of phytochemical coevolution theory. Am Nat 161 507-522 Cronin G (2001) Resource allocation in seaweeds and marine invertebrates chemical defense patterns in relation to defense theories. In McClintock JB, Baker BJ (eds) Mar Chem Ecol. CRC, Boca Raton, FL, pp 325-354... 

Iron Contact Plant.—The fundamental and secondary chemical reactions involved in this process having been considered, there remains only the plant, and the actual fuel consumption per 1000 cubic feet of hydrogen to be described. 

Osbourn AE et al (2003) Dissecting plant secondary metabolism - constitutive chemical defences in cereals. New Phytol 159 101... 

Many thousands of secondary plant compounds have been identified and 400000 are suspected to exist. These numbers provide a great incentive for chemical prospecting (Eisner, 1989). The most prevalent, broad classes of plant secondary compound are phenolics, alkaloids, and terpenoids (Table 11.1). 

At the cellular level, plant secondary metabolites have five major effects on herbivores (a) alteration of DNA replication, RNA transcription, and protein synthesis (b) alteration of membrane transport processes (c) enzyme inhibition and activation (d) blocking of receptor sites for endogenous chemical transmitters and (e) affecting the conformation of other macromolecules (Robinson, 1979). 

How much a mammal eats of a given plant often depends on the levels of different classes of chemical constituent, notably nutrients and plant secondary metabolites. As in birds, it is not the plant defense compounds alone, but rather complex balances between nitrogen and carbohydrate contents, levels of defense compounds, and fiber that determine palatability. 

Foley, W. J., McLean, S., and Cork, S. J. (1995). Consequences of biotransformation of plant secondary metabolites on acid-base metabolism in mammals a final common pathway Journal of Chemical Ecology 21,721-743. 

Cyanobacterial toxins (both marine and freshwater) are functionally and chemically a diverse group of secondary chemicals. They show structure and function similarities to higher plant and algal toxins. Of particular importance to this publication is the production of toxins which appear to be identical with saxitoxin and neosaxitoxin. Since these are the primary toxins involved in cases of paralytic shellfish poisons, these aphantoxins could be a source of PSP standards and the study of their production by Aphanizomenon can provide information on the biosynthesis of PSP s. The cyanobacteria toxins have not received extensive attention since they have fewer vectors by which they come in contact with humans. As freshwater supplies become more eutrophicated and as cyanobacteria are increasingly used as a source of single cell protein toxic cyanobacteria will have increased importance (39). The study of these cyanobacterial toxins can contribute to a better understanding of seafood poisons. 

Both 15 and 16 are involved in plant defense, they may have a role in the flavor spectrum, and their concentration can influence the nutritional safety and quality of food crops. For example, Soledade and colleagues demonstrated the crucial role of indole-3-aldoxime in the biogenesis of cruciferous defense against fungi-induced plant diseases. This is achieved by inserting the indolyl moiety via indole-3-aldoxime, which is a precursor of several secondary chemical defense metabolites of cruciferae. 

It is possible that these ecoregulatory enzymes, used by the insect to inhibit targeted plant toxlficatlon systems, may themselves be the principal target of the production of tannins by plants. The discovery of other examples of secondary chemical interactions with enzymes dedicated to the regulation of toxifica-tion and detoxification mechanisms may be expected as our knowledge of chemically mediated plant-insect interaction expands. 

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