Changes in glycosylated flavonoids in soybean (Glycine max (L.) Merr. cv. “Nam Dan”) leaves under aphid infestation

Abstract

Changes in contents of glycosylated flavonoids in leaves of soybean (Glycine max (L.) Merr. cv. “Nam Dan”) in the flowering stage under infestation of cowpea aphid (Aphis craccivora Koch) was investigated. A strong decrease in the level of glycosylated flavonoids, e.g., genistein 7-O-glucoside, 2’OH genistein 7-O-glucoside, 2’OH genistein malonyl glucoside, after 48-96 hours post-infestation (hpi) of aphid. Levels of these compounds in aphid-infested leaves were remarkably lower than those in controls. Whereas, genistein and total flavonoids in the aphid-infested leaves were induced to higher contents than that observed in control. Activity of important enzymes regarding biosynthesis of flavonoids such as phenylalanine ammonia-lyase (PAL, EC. 4.3.1.5), chalcone synthase (CHS, EC 2.3.1.74) and chalcone isomerase (CHI, EC 5.5.1.6) in the aphid-infested leaves strongly increased during experiemntal time. An increase in acitivity of those enzymes was proportional with the induced decrease of the glycosylated flavonoids and an accumulated increase of genistein and total flavonoids. These results indicate that, changes in the glycosylated flavonoids occured in soybean “Nam Dan” leaves infested by cowpea aphid may connect to a protective mechanism in this soybean cultivar in the flowering stage.