Phytoalexin accumulation

Lo, S.-C. et al., Phytoalexin accumulation in sorghum identification of a methyl ether of luteolinidin, Physiol Mol. Plant Pathol, 49, 21, 1996. 

Wotton, H.R. and Strange, R.N. (1987). Increased susceptibility and reduced phytoalexin accumulation in drought-stressed peanut kernels challenged with Aspergillus flavus , Applied and Environmental Microbiology, 53, 270-273. 

UV-C technology is widely used as an alternative to chemical sterilization and microorganism reduction in food products (Lamikanra 2002 Fan and others 2008). Ultraviolet light also induces biological stress in plants and defense mechanisms in plant tissues with the consequent production of phytochemical compounds (Lee and Kader 2000). Phytoalexin accumulation could be accompanied by other inducible defenses such as cell-wall modifications, defense enzymes, and antioxidant activity, which have been reported with health benefits (Gonzalez-Aguilar and others 2007). It is well documented that UV-C irradiation has an effect in secondary metabolism. 

Specific Control of Phytoalexin Accumulation by "Metabolite Shunting" of Biosynthetic Pathways. Graham and coworkers (personal communication), at the Monsanto Laboratories, St. Louis, have developed techniques to selectively shunt defensive metabolites, particularly of the shikimic acid cycle. Through various techniques, certain compounds are applied to plant aerial or root parts, and these compounds have the property of inducing specific accumulations of secondary metabolites. The directions of these accumulations are under known enzymic control (48), and the regulation of these enzymes is achieved by selecting appropriate inducers. Such inducers seem to provide a novel approach to the control of insects by magnifying the ability of plants to produce and concentrate antiherbivory compounds. 

Further support for the hypothesis that Ca2+ plays a central role in regulating phytoalexin accumulation is provided by experiments in which the turnover of phosphatidylinositol was measured in the plasma membrane of elicitor-treated carrot cells [17]. The carrot cells were first labelled with [3H]myo-inositol and, after the addition of elicitors, acid extracts of the cells were analyzed chromatographically for the production of inositol trisphosphate (IP3). In cells treated with elicitor, the release of radioactive IP3 increased with time and attained a maximum at 3 - 5 min after treatment. Phospholipase activity responsible for the degradation of phosphorylated phosphatidylinositol increased correspondingly. Several reports have shown that IP3 induces rapid release of Ca2+ from intracellular stores in animal cells [18, 19]. Studies on plant cells have also demonstrated that exogenous IP3 releases Ca2+ from microsomal preparations at micromolar concentrations, although only limited... 

Dereks W, Creasy LL. 1989. Influence of fosetyl-Al on phytoalexin accumulation in the Plasmopara viticola-grapevine interaction. Physiol Mol Plant Pathol 34 203-13. 

Kodan A, Kuroda H, Sakai F. 2002. Stilbene synthase from Japanese red pine (Pinus densiflora) implications for phytoalexin accumulation and down-regulation of flavonoid biosynthesis. Proc Natl Acad Sci USA 99 3335-3339. 

Hahlbrock, K., Kreuzaler, F., Ragg, H., Fautz, E. Kuhn, D.N. (1982). Regulation of flavonoid and phytoalexin accumulation through mRNA and enzyme induction in cultured plant cells. In Biochemistry of Differentiation and Morphogenesis, ed. L. Jaenicke, pp. 34-43. Berlin Springer-Verlag. 

When metalaxyl was used, necrotic reactions in susceptible crop cultivars similar to those of resistant ones, as well as phytoalexin accumulation, have been reported (12, 13, 21, 37, 41, 45). Here the use of metalaxyl-resistant strains could also clarify the signifi-... 

Bailey, J.A. Mechanisms of phytoalexin accumulation. In Phytoalexins. Bailey, J.A., Mansfield, J.W., eds., New York, USA John Wiley and Sons. 1982. 

Sharp, J. K., Valent, B., and Albersheim, P. 1984. Purification and partial characterization of a P-glucan fragment that elicits phytoalexin accumulation in soybean. J. Biol. Chem. 259, 11312-11320... 

Aliette (aluminum tris-0 ethylphosphonate) has been reported to enhance defense reactions and phytoalexin accumulation in grapes and tomatoes in response to infection by Plasmopara viticola and Phytophthora spp., respectively, and to trigger phenolic accumulation and hypersensitive cell death in tomatoes, peppers, and beans in response to infection while possessing little direct fungitoxicity (116,117). However, recent data cast doubt on the earlier reports of the low activity of Aliette as an inhibitor of Phytophthora sporulation mi vitro (118), and have attributed the protective properties of the compound to phosphorous acid which is formed in plant tissues or in certain buffer solutions of Aliette (119,120). Toxicity of phosphorous acid to Oomycetes is reversible by phosphate ion, and this may explain Aliette s lack of fungitoxicity in certain growth media. 

Curzate appears to stimulate hypersensitive cell death and phytoalexin accumulation in grapevines infected with P1asmopara viticola (104). 

PAL Induction and phytoalexin accumulation Is common to a wide range of host-parasite Interactions when plants are treated with ellcitors (41). Studies with several plant cell cultures also Indicated that PAL activities are readily Increased by ellcitors (11). 

Ellcitors have been widely used in studies of defense gene activation (for reviews see 3,58). Since It Is simpler to treat plant cells with ellcitors, as opposed to Intact pathogens, results are not compromised by other components of the pathogen. There has been the tendency, however, to assume that If a substance causes induction of early defense genes such as phenylalanine ammonia lyase, then It Is necessarily a phytoalexin ellcitor. Ebel et a1. (M) showed, however, that some substances which activate early defense genes do not lead to phytoalexin accumulation. Therefore, ellcitors should be carefully checked to ensure that they In fact activate phytoalexin pathways. 

In the first years of phytoalexin research, most attention was given to crop plants, which are mostly herbs, and it was not clear whether trees responded in the same way. We now know that several trees are capable of phytoalexin accumulation. 

Plant tissue culture is an extremely useful tool for investigating biochemical and hormonal aspects of plant metabolism. Such systems have been applied to studies of host-pathogen interactions and secondary metabolism. My laboratory has been investigating the biochemical regulation of phytoalexin accumulation in host-pathogen interactions of cultured legumes. 

It is clear from earlier reports (18-19-20) and the data in Tables II and III that production of medlcarpln and maacklaln in response to ellcltors is retained In cultured cells and, most Importantly, that biochemical regulation of phytoalexin accumulation Is not lost. 

The data summarized here provide preliminary evidence for regulation of phytoalexin accumulation by thiol and/or disulfide groups In the interior of the plasma membrane. A hypothesis Is proposed oxidation state of the membrane SH groups regulating the phytoalexin response Is maintained by biological thiol/ disulfide ratios in the cytoplasm and by accessibility of these compounds to the membrane SH moieties. 

P. Ossowski, A. Piloth, P. J. Garegg, and B. Lindberg, Synthesis of a glucoheptaose and a glucooc-taose that elicit phytoalexin accumulation in soybean, J. Biol. Chem., 259 (1984) 11337-11340. 

Mondolo, L.V, F.Q. Cunha, M.R. Braga, 1. Salgado (2002). Nitric oxide synthase-mediated phytoalexin accumulating in soybean cotelydons in response to the Diaporthe phaseolorum f sp. Meridionalis elic-itOT. Plant Physiol. 130, 1288-1297. 

The stem and root-infecting pathogen of soyhcdja, Phytophthora megasperma, excretes glycoproteins. They have proved to be poor, non-specific elicitors of phytoalexin accumulation. 

In one laboratory, a time-course study was carried out to determine the relationship of growth and aflatoxin production by A. flavus to phytoalexin accumulation by intact peanut kernels. Wotton and Strange (23) reported that following inoculation, A. flavus grew logarithmically for 2 days. However, by the third day when the... 

The production of phytoalexins in response to microbes requires a mechanism which enables the plant to recognize the invading organism and subsequently leads to the stimulation of phytoalexin synthesis at the site of microbial penetration. Substances of microbial origin which mediate phytoalexin accumulation in plants have been called elicitors(Ref. 2) and it has been shown in several cases that the culture medium of pathogens contained components which elicited phytoalexin accumulation in the pathogen s host (Ref. 3). Studies on the nature of elicitors have resulted in the partial purification and characterization of a number of molecules from different microbial sources. Elicitors have been reported to have a dependence for activity on a polypeptide or protein (Ref. 4), a glycoprotein (Ref. 5), or polysaccharide (Ref. 6) component. 

Most of the phytoalexins studied to date are from the Fabaceae and the Solanaceae (Kuc, 1992), a fact that probably reflects the economic importance of these families but may also reflect the stability and ease of isolation and characterization of the phytoalexins. At least 200 phytoalexins are known (Brooks and Watson, 1985). Although it is widely accepted that phytoalexins play a major role in disease resistance, their role in disease resistance is less well understood than their production and metabolism (Dixon et al., 1983 Kuc, 1992). Interestingly, in some susceptible reactions between fungi and plants, phytoalexins accumulate to higher... 

Hahn, M. G., A. G. Darvill, and P. Albersheim, Host-pathogen interactions. XIX. The endogenous elicitor, a fragment of a plant cell wall polysaccharide that elicits phytoalexin accumulation in soybeans. Plant Physiol., 68, 1161-1169 (1981). 

A number of sesquiterpene phytoalexins accumulate in potato (Solanum tuberosum) in response to attack by Monol-inia fruticola, Phytophthora infestans, mdAlternaria solani. Among these are rishitin (32), lubimin (33), phytotuberin (34), and several other sesquiterpenes (Brooks and Watson, 1985 Kuc, 1992). Cell walls of P. infestans contain an elici-tor of ph) oalexin accumulation in potato (Kuc, 1982). Similar phytoalexins are synthesized by a number of other solana-... 

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