Antimicrobial compounds phytoalexins

In this section, based on the methodology presented in the previous section, we describe multidimensional fluorescence imaging and its application to tracking cell responses. We developed the time- and spectrally-resolved fluorescence imaging system based on line illumination, which is capable of rapid acquisition of fluorescence intensities as a function of Em, x, and xy-positions. We applied it to the analysis of an induced plant defense response, that is, the accumulation of antimicrobial compounds or phytoalexins, in oat (Avena sativa). 

Phytoalexins are low-molecular-mass antimicrobial compounds that are formed de novo after microbial infection (ii). They provide one strategy of the multi-component pathogen defence program. Many of the over 200,000 plant secondary metabolites are either constitutive or inducible antimicrobial agents. 

The concept of plants being able to produce defensive substances, called phytoalexins, in response to infection was first proposed by Muller and Borger (1). Phytoalexins are presently defined as low molecular weight antimicrobial compounds that are synthesized by and accumulate in plants after their exposure to microorganisms. 

Upon attack by pathogenic micro-organisms, higher plants are known to produce antimicrobial compounds as defense substances. These allelochemicals are called phytoalexins. I chose several phytoalexins as my synthetic targets. Synthesis of some of the phytoalexins will be discussed in this section. 

It is envisioned that the defensive systems of plants include preformed physical and chemical barriers as well as inducible defenses that also can be either physical or chemical. An example of an inducible defense is the synthesis of specific antimicrobial compounds such as phytoalexins or phytoanticipins. However, in other instances plants react to pests by developing long-lasting, broad-spectrum systemic resistance to later attacks by pathogens. This type of resistance is referred to as systemic acquired resistance, and was discovered in tobacco by Ross (1961). This form of resistance is almost universally... 

Mansfield, J.W., Antimicrobial compounds and resistance The role of phytoalexins and phytoanticipins, in Mechanisms of Resistance to Plant Diseases, Slusarenko, A.J., Fraser, R.S.S., and Van Loon, L.C., Eds., Kluwer Academic Publishers, Dordrecht, The Netherlands, 2000, pp. 325-370. 

Phytoalexins are low molecular weight, antimicrobial compounds that are both synthesized by and accumulated in plants after exposure to microorganisms [1.]. Several lines of evidence suggest that these compounds have an important role in plant disease and pest resistance [12.]. ... 

The best documented evidence for an extractive (pinosylvins) functioning as a phytoalexin (an antimicrobial compound produced as an active response of the plant to the pathogen) is the reaction zones produced in pine in response to invasion by Heterobasidion annosum, the Sirex-Amylostereum complex, and the Den-droctonus- idin fungi complex (20). As with other phytoalexins, the accumulation of sitilbenes in pine sapwood is a nonspecific response to injury. In some cases the wounding agent causes rapid death of the invaded tissue and no stilbene... 

Bajsa, J. et al. (2007) A survey of symthetic and natural phytotoxic compounds and phytoalexins as potential antimicrobial compounds. Biol. Pharm. Bull. 30, 1740-1744... 

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