Phytoalexins formation

Hinderer W, Flentje U, Barz W. 1987. Microsomal isoflavone 2- and 3-hydroxylases from chickpea (Cicer arietinum L.) cell suspensions induced for pterocarpan phytoalexin formation. FEBS Lett 214 101-106. 

Yamada, A., Shibuya, N., Kodama, O. and Akatsuka, T. 1993. Induction of phytoalexin formation in suspension-cultured rice cells by A/-acetylchito-oligosaccharides. Biosci. Biotech. Biochem. 57, 405-409... 

Secondly, the deacetylated form of chitin, chitosan, does not induce phytoalexin formation in the rice system but is active in other plant culture systems [99]. Glucan elicitors induce phytoalexins in legumes (soybean, chickpea, bean, alfalfa, pea) and solanaceous sp. (potato, sweet pepper) [100]. However, anthraquinone biosynthesis was stimulated in Morinda citrifolia by both chitin and chitosan. The degree of acetylation was found to be important in inducing defense responses. During the first few days of incubation after adding elicitor,... 

The resistance of plants towards disease may well be related to phytoalexin formation, but whatever be the precise function of these compounds, they can only represent one of the complex of factors which operate in disease resistance and immunity. Any protective substances present in the healthy plant must also be important in this connection. A good example of such a substance is provided by our discovery that healthy seedlings of broad bean (Vlcla faba) contain a potent antifungal chemical to which we have given the name Wyerone. 

The importance of terpenoid phytoalexins in resistance to wilts was further demonstrated in studies of temperature effects on resistance and in studies of induced resistance. Increase in temperature from 25 to 30 C causes a marked increase in resistance. This temperature change also slows the rate of sporulation of the fungus and increases the rate of phytoalexin formation by cotton (56). Likewise, treatments that induce resistance also induce pEy toalexin synthesis (57). Phytoalexin synthesis, therefore, is also important to explain environmental effects on disease resistance. 

Ref. 6) established that potato-cell suspension cultures synthesize and accumulate sesqulterpenold phytoalexins. This ability to elicit terpenoid phytoalexin formation In cell suspension culture should speed the exploitation of tissue culture techniques In the studies of terpenoid phytoalexin biosynthesis. 

The reaction of wasabi phytoalexin (109) with excess 15% aqueous NaSMe gives methyl 2-methylthioindole-3-carboxylate (184,70%) and 140 (20%). In this reaction, formation of 2-methylthioindole-3-carboxylic acid (185) is not observed under various reaction conditions. The fact indicates that once 140 is formed, it does not undergo nucleophilic substitution reaction. In addition, hydrolysis of the... 

The formation of phytoalexins such as glyceollins and phaseollins requires C-prenylation by a range of pterocarpan prenyltransferase (PTP) activities, with dimethylallyl pyrophosphate (DMAPP) as the prenyl donor. For glyceollins and phaseollins, prenylation occurs at position C-2 or C-4 of glycinol or C-10 of 3,9-dihydroxypterocarpan. ° ° However, there are differing activities in other species. For example, in Lupinus albus (white lupin) a prenyltransferase acting at the C-6, -8, and -3 positions of isoflavones has been identified.PTPs have also been characterized in detail for the formation of prenylated flavanones in Sophora flavescens (see, e.g., Ref. 207). However, no cDNA clones for flavonoid-related prenyltransferases have been published to date. 

Liu, C.J. and Dixon, R.A., Elicitor-induced association of isofiavone 0-methyltransferase with endomembranes prevents the formation and 7-0-methylation of daidzein during isofiavonoid phytoalexin biosynthesis. Plant Cell, 13, 2643, 2001. 

In the publication by Nielsen et al. (2004) images of the pigmented inclusions that contain the phytoalexins were prepared by confocal microscopy. This provided a three-dimensional perspective of inclusion body formation and visualization of the phytoalexins. A representation of deoxyanthocyanidin accumulation is shown in Figure 6-3 where inclusions begin to form by 5 to 8 hours after a fungal appressorium was formed by a hypha. 

In either of the proposed pathways, salicylic acid is synthesised from tram-cinnamic acid. This is an intriguing observation and may provide a clue as to how and why the induction of SAR is tightly linked to the formation of a necrotic lesion. When plants react hypersensitively to pathogen attack, many biochemical changes occur, including the induction of phenylpropanoid biosynthesis. In bean, as well as other plants, this induction seems to be at least partly caused by an increase in the synthesis of phenylalanine ammonium lyase and other enzymes involved in the biosynthesis of isoflavonoid phytoalexins, flavonoid pigments and... 

Despite the act that the new compounds have been known and available for years, relatively little is known about their mode of action. Table VI reflects the state of the art. The lack of information is particularly surprising in the case of fosetyl and metalaxyl as far as their indirect effect is concerned, that is, the stimulation of the host plant s defense reactions (e.g. formation of phytoalexins). It is for the first time in the history of fungicides that such effects have been reported. 

Biotic Agents. It is well-established that treatment of plants with virulent or avirulent forms of a pathogen, or with a non-pathogen, may induce the formation of fungitoxic compounds (phytoalexins) which prevent or retard subsequent infection by a pathogen. The phytoalexins are formed at the site of inoculation and are not transported to other plant parts. 

Furstner and coworkers have continued to explore the titanium-mediated formation of indoles from o-V-diacylanilines. The use of a sodium-aluminum oxide mixture prepared from alumina and molten sodium was developed. This material has the advantage over potassium-graphite of being non-pyrophoric. <95S63> Additional specific applications of the reaction were also reported, for example the synthesis of the phytoalexin camalexin, 21b. <95T773>... 

A further example of the effectiveness of these reagents is demonstrated in the synthesis of the complex spiroventivane phytoalexin-lubiminol 3 (Scheme 1.2).4 Generation in situ of a zinc homoenolate, Et02C(CH2)2ZnCl,3 allows formation of the functionalized cyclopentenone intermediate, essential for the synthesis. 

When plants undergo various stresses, certain secondary metabolites, including defense compounds, accumulate. Several secondary metabolites such as terpenoid indole alkaloids, indole glucosinolate, nicotine alkaloids, and polyamines are known to accumulate through the induction of biosynthetic genes by jasmonates.898-900 MeJA also induces genes involved in the formation of tryptophan derivatives, terpenoid indole alkaloids.901 These compounds are known to be involved in defense response to pathogen attack as phytoalexins. 

The addition of a second, reducing end acceptor and a thiophilic promoter (NIS) resulted in trisaccharide formation. Yields as high as 84% for the overall process were reahzed, showcasing the efficiency of this strategy as well as the promoter compatibility, which can be a problem (Fig. 3). The method has been extended to branched structures as well (34). Takahashi has advanced the orthogonal OPG strategy in an impressive synthesis of the heptasaccharide phytoalexin elicitor (HPE) in 24% overall yield (35). 

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