Cell Oomycetes

Mikes V (1997) The fungal ehcitor cryptogein is a sterol carrier protein. FEES Lett 416 190 Ponchet M et al (1999) Are ehcitins cryptograms in plant-Oomycete communications Cell Mol Life Sci 56 1020... 

Cell wall 0.1-0.25 Zygomycetes, Ascomycetes and Basidiomycetes contain chitin (2-26% dry wt) Oomycetes contain cellulose, not chitin yeast cells contain glucan (29%), mannan (31%), protein (13%) and lipid (8.5%)... 

Among the fungi, the class Oomycetes is by number the smallest of the five classes, comprising some 70 genera with 500 species. However, in many respects, they are a unique and important class 1) their cell walls differ from those of all other fungi, inasmuch as they contain cellulose instead of chitin 2) they do not synthesize sterols 3) their life cycle is diploid (in contrast to all other fungi) and 4) they form motile spores (zoospores). 

Until about ten years ago, protectant foliar fungicides (such as ethylene bis-dithiocarbamates and phthalimides) and soil sterilants (such as vapam or methylbromide) were the only chemical means of controlling diseases caused by Oomycetes. These compounds are nonspecific biocides affecting many vital cell processes of both the pathogen and the host plant. This means that they are non-selective,... 

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. 

The best examples of adhesion resulting from the stimulus of contact are found among the Oomycetes where zoospore encystment occurs upon contact with the host. Zoospores are motile propagules that lack cell walls. These cells often require specific sites on a host root for attachment and eventual penetration. 

The oomycetes, hyphochytrids, labyrinthuloids, and thraustochytrids are included in the kingdom Heterokontobionta or pseudofungi [54] based on the presence of cellulose in their cell walls, a tubular mitochondrial crista, hetero-kont flagella, one decorated with tripartite hairs, and the a, (3-diaminopimelic acid lysine biosynthetic pathway. The slime molds were classified into the kingdom Protozoa [38]. 

Brian (1949) presumed that griseofulvin affected the morphogenesis of the chitinous cell walls in fungi, and thus explained the nonsensitivity of fungi with cellulose cell walls (Oomycetes, yeast fungi) and of bacteria to this antibiotic. 

F4 28 Cell membrane permeability, fatty acids (prop.) Carbamates Propamocarb Specific for Oomycetes... 

The covalent binding property of benzamides has been exploited in the development of cell-based competitive binding assays that measure the ability of other antitubulin agents to inhibit binding of radiolabeled benzamides to j -tubulin in whole cells. The tritiated S-enantiomer of zoxamide has been used to study the zoxamide binding site in the Oomycete Phytophthora capsid [7]. Tritiated analogs 2 and 3 (RH-4032 and RH-5854, Fig. 16.1.2) have been used in similar assays in plant [4] and mammalian cells [6], respectively. 

Fig. 19.6. I mmunofluorescent localization of spectrin-like protein(s) in hyphae of P. infestans treated with fluopicolide and known anti-oomycetes. Control cell (a) or treated with 10 ppm of fluopicolide (b), 10 ppm of iprovalicarb (c), 10 ppm of fenamidone (d), 10 ppm of dimethomorph (e), 10 ppm of metalaxyl (f) and 10 ppm of zoxamide (g), 2 h post-treatment.

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