Phytoalexin

About: Phytoalexin is a research topic. Over the lifetime, 1161 publications have been published within this topic receiving 63405 citations. The topic is also known as: phytoalexins.

Detection and cellular localization of elemental sulphur in disease-resistant genotypes of Theobroma cacao

Abstract: DISEASE-RESISTANT genotypes are the basis for controlling many major microbial pathogens of economic plants. Resistance is often linked with organic, antimicrobial phytoalexins, produced de novo in cells surrounding apoptotic or 'hypersensitive' cells that die rapidly after contact with incompatible pathogens1–3. Here we report the production by resistant genotypes of Theobroma cacaoof four phytoalexins in response to a xylem-invading fungal pathogen; these comprised two phenolics, a triterpenoid and, highly unusually in a higher eukaryote, elemental sulphur as cyclooctasulphur S8. Energy-dispersive X-ray microanalysis revealed a high accumulation of sulphur only in cells and structures in potential contact with the vascular pathogen; that is, xylem parenchyma, xylem vessel cell walls and gels occluding vessels. Our data provide a rare example of cellular localization of an antimicrobial substance and evidence for the first time for accumulation of elemental sulphur in a plant linked with a resistance response; this discovery comes centuries after man first used elemental sulphur as a potent fungicide4,5.

Comparison of proteinase inhibitor-inducing activities and phytoalexin elicitor activities of a pure fungal endopolygalacturonase, pectic fragments, and chitosans.

Abstract: Rhizopus stolonifer endopolygalacturonase, an elicitor of casbene synthetase activity in castor bean seedlings, was found to be a potent elicitor of the phytoalexin pisatin in pea pods and of proteinase Inhibitor I in tomato leaves. The enzyme was an active elicitor or inducer only in its active native state; heat-denatured enzyme was inactive in all three systems. The activities of (a) the tomato pectic polysaccharide proteinase inhibitor-inducing factor, (b) a partially acid hydrolyzed proteinase inhibitor-inducing factor, (c) citrus pectic fragments, and (d) chitosan, were also compared in the three bioassay systems. The four oligosaccharide preparations were active in all three systems, but with different degrees of potency. In tomato leaves and pea pods, chitosans were most active, whereas in castor beans, the citrus pectic fragments were the best elicitors. The data presented support the hypothesis that plant and fungal cell wall fragments are important signals in mobilizing a wide variety of biochemically different types of plant defense responses, and that endopolygalacturonases play a key role in releasing the plant cell wall fragments during pest attacks.

Resveratrol production as a part of the hypersensitive‐like response of grapevine cells to an elicitor from Trichoderma viride

Abstract: SUMMARY Suspension cell cultures of grapevine (Vitis vinifera, cv. Monastrell) treated with an elicitor (cellulase, Onozuka R-10) from Trichoderma viride showed a hypersensitive-like response. This was characterized by cell plasmolysis and was accompanied by localized cell death, which was concomitant with cell culture browning, itself probably due to an activation of oxidative phenolic metabolism driven by a large increase in endogenous levels of H2O2. In addition to these responses, the treatment of cell cultures with the elicitor produced an increase in amounts of benzoic acid and of resveratrol, the latter a potent phytoalexin of grapevines. This hypersensitive-like response was specific since none of the above responses was obtained with other cell wall-degrading enzymes from several sources, or with inocula of either mycelial extracts or culture filtrates of Botrytis cinerea. These results are discussed in the light of a disease-resistance reaction induced in grapevine cells by a product of T. viride, a fungal agent characterized by its effective biocontrol of Botrytis cinerea, the causal agent of grey mould in grapevines.

Early physiological responses of Arabidopsis thaliana cells to fusaric acid: toxic and signalling effects

Abstract: Summary • Fusaric acid (FA) is a toxin produced by Fusarium species. Most studies on FA have reported toxic effects (for example, alteration of cell growth, mitochondrial activity and membrane permeability) at concentrations greater than 10−5 m. FA participates in fungal pathogenicity by decreasing plant cell viability. However, FA is also produced by nonpathogenic Fusarii, potential biocontrol agents of vascular wilt fusaria. The aim of this study was to determine whether FA, at nontoxic concentrations, could induce plant defence responses. • Nontoxic concentrations of FA were determined from cell-growth and O2-uptake measurements on suspensions of Arabidopsis thaliana cells. Ion flux variations were analysed from electrophysiological and pH measurements. H2O2 and cytosolic calcium were quantified by luminescence techniques. • FA at nontoxic concentrations (i.e. below 10−6 m) was able to induce the synthesis of phytoalexin, a classic delayed plant response to pathogen. FA could also induce rapid responses putatively involved in signal transduction, such as the production of reactive oxygen species, and an increase in cytosolic calcium and ion channel current modulations. • FA can thus act as an elicitor at nanomolar concentrations.

Molecular cloning and characterization of a cDNA encoding ent‐cassa‐12,15‐diene synthase, a putative diterpenoid phytoalexin biosynthetic enzyme, from suspension‐cultured rice cells treated with a chitin elicitor

Abstract: Summary We have isolated and characterized a cDNA encoding a novel diterpene cyclase, OsDTC1, from suspension-cultured rice cells treated with a chitin elicitor. OsDTC1 functions as ent-cassa-12,15-diene synthase, which is considered to play a key role in the biosynthesis of (−)-phytocassanes recently isolated as rice diterpenoid phytoalexins. The expression of OsDTC1 mRNA was also confirmed in ultraviolet (UV)-irradiated rice leaves. In addition, we identified ent-cassa-12,15-diene, a putative diterpene hydrocarbon precursor of (−)-phytocassanes, as an endogenous compound in the chitin-elicited suspension-cultured rice cells and the UV-irradiated rice leaves. The OsDTC1 cDNA isolated here will be a useful tool to investigate the regulatory mechanisms of the biosyntheis of (−)-phytocassanes in rice.