Regulation of cabbage (Brassica oleracea capitata) hypocotyl elongation, and infection by Peronospora parasitica, with B-indolylacetonitrile and chloramphenicol

Untreated excised segments of the hypocotyls of dark grown cabbage seedlings are always systemically infected when inoculated with the conidia of the obligate parasite Peronospora parasitica (Downy mildew). Cabbage hypocotyl elongation is promoted by 10^–4M indolylacetonitrile (IAN) and this elongation is inhibited by 100 g mL^–1 chloramphenicol (CAM). The fungus remains localized in 5–8 day old hypocotyl segments exposed to CAM, but this inhibition is reversed by IAN. Indol-3-acetic acid (IAA) has the same effect as IAN. Both gibberellic acid and kinetin inhibit systemic infection. Conidial spore germination is not reduced by the CAM concentration used in these experiments. The success of the pathogen in the host is not correlated with host elongation, but is probably related to a common metabolic site in either host or pathogen affected by both CAM and IAN.Abbreviations IAN indolylacetonitrile - CAM chloramphenicol - IAA indol-3-acetic acid - G gibberellic acid - K kinetin