Isoflavonoid production by adventitious-root cultures of Iris germanica (Iridaceae)

We established the adventitious-root cultures of Iris germanica, a monocotyledonous plant known for isoflavonoid production. Irigenin (5,7,3 -trihydroxy-6,4 ,5 -trimethoxyisoflavone) and iristectorigenin A (5,7,3 -trihydroxy6,4 -dimethoxyisoflavone) along with their 7-O-b-D-glucosides, iridin and iristectorin A, respectively, were found as the major components in adventitious roots in the liquid medium, and the total isoflavone content was about 3.6 mmol per g fresh weight in 3-week-old cultures, which was much higher than the 0.7 mmol per g dry weight in the rhizome previously reported (Ali et al. 1983 Phytochemistry 22: 2061). Abiotic stress was applied by addition of 3 mM cupric chloride (CuCl2) to the liquid medium. The isoflavone glucoside content was increased during the initial 6 h of CuCl2 treatment, which was followed by a decrease; the aglycone level continued to increase throughout the 48 h of treatment. The decrease in glucoside content was negatively correlated with the increase in aglycone content between 6 and 48 h. The total isoflavone content (glucosides aglycones) at 6 h after the start of CuCl2 treatment was 1.4-fold the initial value, and nearly the same content was maintained for 48 h. Thus, the main effect of CuCl2 treatment appeared to be the induction of hydrolysis of isoflavone glucosides. A cDNA of chalcone synthase was cloned, and the mRNA was expressed in the culture producing isoflavones.