Stress responses in alfalfa (Medicago sativa L.). V. Constitutive and elicitor-induced accumulation of isoflavonoid conjugates in cell suspension cultures

• Published in: Plant physiology (Bethesda) Vol. 94; no. 1; pp. 227 - 232
• Main Authors: Kessmann, H. (Samuel Roberts Noble Foundation, Ardmore, OK), Edwards, R, Geno, P.W, Dixon, R.A
• Format: Journal Article
• Language: English
• Published: United States American Society of Plant Physiologists 01.09.1990
• Subjects: Alfalfa; BIOSINTESIS; BIOSYNTHESE; Biosynthesis; Cell culture techniques; Cellular metabolism; Chemical suspensions; Chickpeas; COLLETOTRICHUM; COMPOSICION QUIMICA; COMPOSITION CHIMIQUE; CULTIVO DE CELULAS; CULTURE DE CELLULE; Cultured cells; Enzymes; FITOALEXINA; Isoflavones; MEDICAGO SATIVA; METABOLITE; METABOLITOS; PHYTOALEXINE; Plants
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.94.1.227

The isoflavonoid conjugates medicarpin-3-O-glucoside-6"-O-malonate (MGM), afrormosin-7-O-glucoside (AG), and afrormosin-7-O-glucoside-6"-O-malonate (AGM) were isolated and characterized from cell suspension cultures of alfalfa (Medicago sativa L.), where they were the major constitutive secondary metabolites. They were also found in alfalfa roots but not in other parts of the plant. The phytoalexin medicarpin accumulated rapidly in suspension cultured cells treated with elicitor from Colletotrichum lindemuthianum, and this was subsequently accompanied by an increase in the levels of MGM. In contrast, net accumulation of afrormosin conjugates was not affected by elicitor treatment. Labeling studies with [14C]phenylalanine indicated that afrormosin conjugates were the major de novo synthesized isoflavonoid products in unelicited cells. During elicitation, [14C]phenylalanine was incorporated predominantly into medicarpin, although a significant proportion of the newly synthesized medicarpin was also conjugated. Treatment of 14C-labeled, elicited cells with L-alpha-aminooxy-beta-phenylpropionic acid, a potent inhibitor of PAL activity in vivo, resulted in the initial appearance of labeled medicarpin of very low specific activity, suggesting that the phytoalexin could be released from a preformed conjugate under these conditions. Our data draw attention to the involvement of isoflavone hydroxylases during the constitutive and elicitor-induced accumulation of isoflavonoids and their conjugates in alfalfa cell cultures