The effect of plant age and nodulation on the isoflavonoid content of red clover (Trifolium pratense)

The effect of age and inoculation with nodulating bacteria on the isoflavonoid content of red clover (Trifolium pratense L.) has been determined. Both roots and foliage contained a complex range of conjugated isoflavonoids with formononetin-7-O-glucoside-6 ''-malonate (FGM), maackian 3-O-glucoside-6 ''-O-malonate (MKGM), four acidic (presumed malonylated) 7-O-glycosides of biochanin A (BGMs), and an acidic (presumed malonylated) glycoside of an unknown 5,7-dihydroxy-containing isoflavonoid metabolite termed UN 1GM being the major metabolites in all plant parts. In contrast, the concentrations of the corresponding isoflavonoid aglycones always remained low In the foliage, the order of abundance of the conjugates was FGM > BGM > UN 1GM > MKGM, while in the roots of plants up to 15 days old the order was FGM > BGM = MKGM > UN1GM, changing to MKGM > FGM > BGM > UN1GM in the older roots. In all plant parts the concentrations of these various conjugates were affected differently by plant growth and nodulation. In the foliage, BGM, FGM and UN1GM increased with age and this accumulation was partially suppressed by nodulation. In uninoculated roots MKGM accumulated steadily with age, while overall the concentrations of FGM, BGM and UN1GM remained unchanged. Nodulation suppressed the accumulation of MKGM and resulted in a decline in FGM content. These results suggest that nodulation not only affects isoflavonoid accumulation in the roots but can also systemically regulate isoflavonoid metabolism in the foliage.