Allelochemicals Biologica... - Name

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ANA LUISA ANAYA
phytochelatines, various pest-control effects, and poisoning. Complex biological-biochemical
interactions among roots, rhizosphere organisms, and the rhizosphere solution
determine the overall biogeochemical processes in the wetland rhizosphere and
in the vegetated wetlands. In order to comprehend how wetlands really function and
to understand these interactions it is necessary to implement long-term collaborative
research (Neori et al., 2000). We can find promising allelochemicals and useful interactions
in the rich biodiversity of these particular ecoystems, but without doubt, in all
type of ecosystems.
3. CHEMISTRY OF ALLELOPATHY
As we know, plant and microbial compounds are continuously analyzed as potential
sources of herbicides, pesticides, and pharmaceuticals because they provide a diversity
of carbon skeletons and there has been success in that a number of compounds
have shown biological activity. The same bioassays and techniques to reveal mechanisms
of action apply to the search for herbicides as in the study of allelopathy. Certainly
there is overlap in goals and compounds studied, but there also is a difference
in that the starting point in the ‘herbicide search’ might be any natural product, as
opposed to one identified with allelopathy. Most inhibitors of plants are secondary
compounds that have their origin in either the shikimate or acetate pathways, or they
are compounds having skeletal components from both of these origins (Einhellig,
2002). Waller et al. (1999) listed over twenty classes of secondary metabolites that are
produced, stored, and released into the rhizosphere where they have biological activity
as well as undergo microbial transformation and degradation. Einhellig (2002)
concluded that the 14 categories suggested by Rice (1984) are sufficiently broad to
still retain validity: water-soluble organic acids, straight-chain alcohols, aliphatic
aldehydes and ketones, unsatured lactones, long-chain fatty acids and polyacetylenes,
naphthoquinones, anthraquinones and complex quinones, gallic acids and
polyphloroglucinols, cinnamic acids, coumarins, flavonoids, tannins, terpenoids, and
steroids, amino acids, and purines and nucleosides.
In this chapter some of the main compounds and studies associated with allelopathy
will be mentioned.
Terpenoids and phenolics are the most common compounds involved in allelopathic
interactions. Terpenoids are the largest group of plant chemicals (15,000-20,000)
with a common biosynthethic origin. The terpenoid pathway generates great structural
diversity and complexity of compounds, thus generating enormous potential for
mediating ecological interactions (Duke, 1991; Langenheim, 1994). Terpenoids may
produce effects on seeds and soil microbiota through volatilization, leaching from
plants, or decomposition of plant debris. These interactions can significantly affect
community and ecosystem properties, although studies of plant-plant chemical interactions
have often been controversial because of difficulty in unambiguously demonstrating
interference by chemical inhibition rather than through resource competition
or other mechanisms (Harper, 1977).