Investigation of the mechanism of phytoalexin accumulation in soybean induced by glucan or mercuric chloride

Soybean cotyledons which had been treated with glucan from Phytophthora megasperma f.sp. glycinea or with mercuric chloride were pulse-labeled with ¹⁴CO₂ and then the ¹⁴C-incorporation into the phytoalexins was determined. The kinetics of ¹⁴C-incorporation into phytoalexins (glyceollin isomers and 3,6α,9-trihydroxypterocarpan) was very similar with the two types of elicitors. Metabolic rates of phytoalexins were determined by pulse-chase experiments. The apparent half-life of metabolism was about 100 h for glyceollin with either glucan or HgCl₂. The half-lives for trihydroxypterocarpan were 39 h with glucan and 14 h with HgCl₂. According to our results levels of glyceollins in soybean cotyledons are mainly controlled by their rates of synthesis. Biotic (glucan) and abiotic (HgCl₂) elicitors have similar induction effects. Both types of elicitors could act by effecting the release of endogenous elicitors.