Effect of some soybean and bean phytoalexins and related isoflavonoids on growth of Candida albicans.
The influence of a series of related isoflavonoids on growth of the zoopathogenic yeast, Candida albicans, in liquid media was studied. The order of effectiveness was identical with that previously found for a range of phytopathogenic fungi. Minimum inhibitory concentration of phaseollinisoflavan, the most active test compound, was 250 microM for 3 days after inoculation. However, C. albicans resumed growth thereafter. Phaseollinisoflavan, 500 microM, did not inhibit but only delayed growth of the yeast. Tolerance of C. albicans to phaseollin and phaseollinisoflavan was based on nondegradative mechanism(s), while tolerance to glyceollin appeared to be based on detoxification.
Differential sensitivity of Phytophthora megasperma f.sp. glycinea isolates to glyceollin isomers
Abstract Glyceollin isomers I, II and III were extracted from soybean cotyledons (cv. Harosoy 63) inoculated with Phytophthora megasperma f.sp. glycinea race 1, and separated and purified by column, high performance and thin layer chromatography and quantitated by spectrophotometry. The extinction coefficient of glyceollin I was 10 800, that of glyceollin II and III conformed to published values. Glyceollin I (ED50 approx. 33 μg ml−1) was almost twice as inhibitory as glyceollin II and III to growth of P. megasperma f.sp. glycinea race 1 on V8 juice agar. All three isomers were less active in soybean hypocotyl extract agar. Glyceollin II (ED50 7 μg ml−1) was the most active against zoospore germination, and caused zoospores to burst; ED50 values for glyceollin I and III were 12·2 and 13·9 μg ml−1 respectively. Three isolates (1·1, 1·2, 1·3) were obtained from sectors in colonies on agar medium amended with glyceollin I, II or III respectively. Isolates 1·1 and 1·3 grew more rapidly on medium amended with glyceollin I, III or a natural glyceollin mixture than did wild type P. megasperma fsp. glycinea race I. All isolates and wild type had similar growth rates on medium amended with glyceollin II. The isolates did not lose their tolerance when grown on control medium and are presumably genetically controlled variants. Tolerance of glyceollin did not increase the aggressiveness of the isolates on soybeans.
Biosynthesis of glyceollins I, II and III in soybean
Abstract In a series of feeding experiments using CuCl 2 -treated soybean ( Glycine max ) seedlings and pods, 14 C-labelled phenylalanine, daidzein, 7,2′,4′-trihydroxyisoflavone, 3,9-dihydroxypterocarpan and glycinol (3,6a,9-trihydroxypterocarpan) were all good biosynthetic precursors of the phytoalexins glyceollins I, II and III. The results confirm that the prenylation step occurs after the 6a-hydroxypterocarpan skeleton of glycinol has been synthesized. The proportions of the individual glyceollins isolated from seedlings or pods dittered markedly, being ca 2: 1: 2 for glyceollins I, II and III, respectively, in seedlings, and 5: 3: 1, respectively, in pods.