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Phytoalexin synthesis by the sorghum mesocotyl in …
Oligosaccharins, which can result from normal development or pathogen attack, serve a variety of functions including: (a) stimulate ethylene synthesis; (b) induce phytoalexin (defense chemicals produced in response to a fungal/bacterial infection) synthesis; (c) induce chitinase and other enzymes; (d) increase cytoplasmic calcium levels and (d) cause an "oxidative burst". This burst produces hydrogen peroxide, superoxide and other active oxygen species that attack the pathogen directly or cause increased cross-links in the wall making the wall harder to penetrate.
Let's look at how this system works. Consider a pathogenic fungus like . In contact with the host plant the fungus releases enzymes such as pectinase that break down plant wall components into oligosaccharins. The oligosaccharins stimulate the oxidative burst and phytoalexin synthesis, both which will deter the advance of the fungus. In addition, the oligosaccharins stimulate chitinase and glucanase production in the plant. These are released and begin to digest the fungal wall. Fragments of fungal wall also act as oligosaccharins in the plant to further induce phytoalexin synthesis. Cool!
Phytoalexins have been defined as antiÂ microbial compounds of low-molecular weight that both are synthesized by and accumulate in plants after the exposure of the plant to microorganisms (113).
Sucrose: A Constitutive Elicitor of Phytoalexin Synthesis
OsKOL4 and OsKOL5 are likely to take part in phytoalexin biosynthesis, because their expression was promoted by UV irradiation and/or elicitor treatment.
One particularly interesting aspect of these compounds originates from the fact that, in many systems, phytoalexin synthesis is strongly enhanced not only upon challenge of plant tissues by parasites but also following treatment with substances called elicitors.
Signal transduction in elicitation of phytoalexin synthesis
Changes in the rates of synthesis of three enzymes of phenyl-propanoid biosynthesis in Phaseolus vulgaris L. (dwarf French bean) have been investigated by immunoprecipitation of [35S]methionine-labeled enzyme subunits with mono-specific antisera. Elicitor causes marked, rapid but transient co-ordinated increases in the rate of synthesis of phenyl-alanine ammonia-lyase, chalcone synthase and chalcone isomerase concomitant with the phase of rapid increase in enzyme activity at the onset of accumulation of phenyl-propanoid-derived phytoalexin antibiotics in suspension cultures of P. vulgaris. Co-ordinate induction of enzyme synthesis is also observed in hypocotyl tissue during race:cultivar-specific interactions with Colletotrichum lindemuthianum, causal agent of anthracnose. In an incompatible interaction (host resistant) there are early increases apparently localized to the initial site of infection prior to the onset of phytoalexin accumulation and expression of hypersensitive resistance. In contrast, in a compatible interaction (host susceptible) there is no induction of synthesis in the early stages of infection, but a delayed widespread response at the onset of lesion formation associated with attempted lesion limitation. It is concluded that expression of the phytoalexin defense response in biologically stressed cells of P. vulgaris characteristically involves co-ordinate induction of synthesis of phytoalexin biosynthetic enzymes.
AB - The total synthesis of the phytoalexin (±)-lubiminol 1 has been accomplished. The synthesis relies on a conjugate addition-cyclization reaction to prepare a photosubstrate for a stereoselective intramolecular photoaddition reaction. The photoadduct is and formed into the required spiro [5.4] decane through a radical fragmentation-rearrangement reaction.
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Co-ordinated synthesis of phytoalexin biosynthetic …
The total synthesis of the phytoalexin (±)-lubiminol 1 has been accomplished. The synthesis relies on a conjugate addition-cyclization reaction to prepare a photosubstrate for a stereoselective intramolecular photoaddition reaction. The photoadduct is and formed into the required spiro [5.4] decane through a radical fragmentation-rearrangement reaction.
CHEMICAL INDUCTION OF PHYTOALEXIN SYNTHESIS …
N2 - The total synthesis of the phytoalexin (±)-lubiminol 1 has been accomplished. The synthesis relies on a conjugate addition-cyclization reaction to prepare a photosubstrate for a stereoselective intramolecular photoaddition reaction. The photoadduct is and formed into the required spiro [5.4] decane through a radical fragmentation-rearrangement reaction.
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