Oomycetes cell wall synthesis

The phenylamide fungicides affect especially hyphal growth and the formation of haustoria and spores in oomycetes [22]. Since spores contain many ribosomes to support early growth stages, RNA synthesis is fully operational only after spore germination therefore, later development stages are most sensitive [19]. As a consequence of RNA inhibition, the precursors of RNA synthesis (i.e., nucleoside triphosphates) are accumulated. They activate j8-l,3-glucan synthetases, which are involved in cell wall formation [19] with the result that metalaxyl-treated hyphae often produce thicker cell walls than untreated ones. 

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