Regulation of Phytoalexin Synthesis in Jackbean Callus Cultures

Abstract

Jackbean, Canavalia ensiformis (L.), calls tsues synthesized the phytoalexin, medicarpin (3-hydroxy-9-methoxypterocarpan), when treated with spore suspensions of Pithomyces chartarum (Berk. and Curt.) M. B. EEs, a nonpathogen ofjackbean. Medicarpin was isolated from treated calu tissue and identfied by its ultraviolet and mass spectra. The minimm spore concentration found to elicit me synthesis after 26 hours was 1 x 105 spores/mI; levels of medicwpin in calls tissue increased linearly up to 1 x 107 spores/ml, indiatg that the recognition sites for presumed elitors were not atn ted. Medicar-pin was first detected in calls treated with 1 x 107 spores/ml, 6 to 12 hours after applction, and the concentration reached a maximm at 48 hours, dowly dedining thereafter to 72 hours. In callos treated with 3.15 mM HgCa,, medicarpin concentrations were also maximum by 48 hours. Phenybaaine ammonia-lyase (EC 4.3.1.5) activity increased 2-fold in spore-treated callus after 36 hours. Isoliquiritigenin, daidzein, and genistein o-methyltrusferase (EC 2.1.1.6) actvities were increased 3-to 4-fold in treated callus. Caffeic acid and naringenin were more effIcient substrtes for o-methyltrasfere activity than the other favo-noids or apigenin, but there was no increase in these o-methyltrnsferase activities in spore-treated callus. The phytoalexin response in this calls tissue culture system compares well with natWal plant systeum and should be an excellent system for investiting regulation of phytoalexin synthesis.