Secondary plant allelochemics

In order for allelochemicals to enter the body of a herbivore, absorption must occur across the gut lining. Curtailing the initial absorption of dietary allelochemicals may be a herbivore s first line of defense against plant toxins. Studies have citied the lack of absorption or metabolism of lipophilic plant secondary metabolites (i.e., terpenes), conducive to phase I or II detoxification, in the gut of terrestrial herbivores rather these compounds are excreted unchanged in the feces (Marsh et al. 2006b). While physical barriers or surfactants have been used to explain this limited adsorption in both marine and terrestrial herbivores (Lehane 1997 Barbehenn and Martin 1998 Barbehenn 2001 for review of marine herbivores, see Targett and Arnold 2001), active efflux of plant allelochemicals out of enterocytes into the gut lumen has received limited attention until now. 

Bolser RC, Hay ME (1996) Are tropical plants better defended Palatability and defenses of temperate vs tropical seaweeds. Ecology 77 2269-2286 Boyle RR, McClean S (2004) Constraint of feeding by chronic ingestion of 1,8-cinole in the brushtail possum (Trichosurus vulpecula). J Chem Ecol 30 757-775 Brattsten LB (1992) Metabolic defenses against plant allelochemicals. In Rosenthal GA, Berenbaum MR (eds) Herbivores their interactions with secondary plant metabolites. Academic, New York, pp 175-242... 

Brattsten, L. B. Metabolic defenses against plant allelochemicals, in Herbivores Their Interaction with Secondary Plant Metabolites Ecological and Evolutionary Processes, Vol. 2, Rosenthal, G. A. and Berenbaum, M. R., Eds., Academic Press, San Diego, 1992, 175. 

Brattsten L. B. (1979) Biochemical defense mechanisms in herbivores against plant allelochemicals. In Herbivores, Their Interaction with Secondary Plant Metabolites, eds G. A. Rosenthal and D. H. Janzen, pp. 199-270. Academic Press, New York. 

In animals, we can observe the analogous situation in that many insects and other invertebrates (especially those which are sessile and unprotected by armor), but also some vertebrates, store secondary metabolites for their defense which are often similar in structure to plant allelochemicals 1,4,12,16,17,28-30,494-496,503). In many instances, the animals have obtained the toxins from their host plants 4,12,15,17,27-33). Hardly any zoologist or ecologist doubts that the principal function of these secondary metabolites (which are often termed toxins in this context) in animals is that of defense against predators or microorganisms 1,17,28,494-496). 

Brattsten, L.B., Biochemical defense mechanisms in herbivores against plant allelochemicals, in Herbivores Their interaction with secondary plant metabolites, Rosenthal, G.A. and Janzen, D.H., Eds., New York Academic Press, 1979, p. 199. 

Of the compounds listed in Table II, chlorsulfuron and acifluorfen (Figure 2, VI and VII, respectively) look particularly interesting with regard to manipulation of allelochemical production. Both of these compounds can cause large increases in the phenolic titre of plant tissues (e.g. Figures 6 7). Suttle et al. (75) suggested that chlorsulfuron would be an excellent chemical for manipulation of the quality and quantity of secondary phenolic compounds in studies of the role of these potential allelochemics in ecological Interactions. 

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... 

There are numerous reports of allelopathy in the literature, but often the identity of the allelochemical(s) is unknown. There are, however, many cases where specific compounds or groups of compounds have been implicated as allelopathic agents. Table 1 summarizes some examples of sources and identities of allelochemicals that directly inhibit plant growth. These secondary compounds have been implicated as a driving force in ecological succession ( 1 ). 

If the allelochemical is hydrophylic, it cannot enter into the cell and act from outside by binding with chemoreceptors. The compounds from allelopathically active plants may serve as chemosignals and their signalling occurs via alternative pathways (i) Chemoreceptor (sensors) — transducers (G-proteins) —> secondary messengers (Ca2+, cyclic AMP or GMP, inositol triphospate, etc) —> organelles or (ii) Chemoreceptor (sensors) —> ion channels —> action potential organelles, or (iii) Chemoreceptor (sensors) —> ion channels —> cytoskeleton— organelles (Roshchina, 2005 a). What is the effect of acted allelochemical on the pathways, could be analysed to study the effects of substances on separate sites of the transduction chain. 

Allelopathy is defined as biochemical interactions between one plant or microorganism (alga, bacteria, or virus) and another plant through the production of chemical compounds - secondary metabolites (allelochemicals), which influence, direct or indirect, harmful or beneficial, plant growth and development (Rice 1984). Allelochemicals are present in almost all plants and in many tissues, like leaves, stems, flowers, fruits, seeds, roots, or pollen and may be released from plants into the environment by volatilization, leaching, root exudation, and decomposition of plant residues (Chou 1990). 

Wadleigh RW, Yu SJ (1988) Detoxification of iso thiocyanate allelochemicals by glutathione transferase in three lepidopterous species. J Chem Ecol 14 1279-1288 Werck-Reichhart D, Feyereisen R (2000) Cytochromes P450 a success story. Genome Biol 1 1-9 Williams AB, Jacobs RS (1993) A marine natural product, patellamide D, reverses multidrug resistance in a human leukemic cell line. Cancer Lett 71 97-102 Yazaki K (2006) ABC transporters involved in the transport of plant secondary metabolites. FEBS Lett 580 1183-1191... 

Rosenthal. G. A. (1991). Nonprotein amino acids as protective allelochemicals. In Herbivores Their Interaction with Secondary Plant Metabolites, vol. 1, ed. G. A. Rosenthal, and M. R. Berenbaum, pp. 1-34. San Diego, CA Academic Press. 

This does not mean that analysis of allelopathy in an arid environment should be done differently from that which is customary in a humid environment yet it is important to estimate the extent to which inorganic salts (excreted by the plant or released from its litter) are involved in the allelopathic effect. So far as secondary metabolites are concerned, it should be of interest to compare their production under humid and stressed conditions. It is suggested that for the evaluation of the allelochemical effect, species suppressed in their natural habitat should be preferred over any other standard seeds commonly used for evaluating germination inhibitors. Also, efforts to isolate allelochemicals from soils will assist in the establishment of allelopathy on a more concrete basis than is available at present. 

Waller, G.R., M.C. Feng, Y. Fujii. Biochemical analysis of allelopathic compounds plants, microorganisms, and soil secondary metabolites. In Principles and Practices in Plant Ecology Allelochemical interactions, Inderjit, Dakshini and Foy C.L. eds. CRC Press, Boca Raton, FL, US A. 1999, pp. 

Any chemical produced by a plant (donor) that stimulates or inhibits the growth of a neighbour (receiver or receptor) is broadly termed an allelochemical. Typically, allelochemicals are secondary metabolites (Whittaker and Feeney 1971 Rice, 1984 Rizvi et al., 1992), produced as by-products of the acetate and shikimic acid pathways. They may also form as degradation products from the action of microbial enzymes... 

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