Abstract
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-α-aminooxy-β-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.
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Selected References
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- Dalkin K., Edwards R., Edington B., Dixon R. A. Stress Responses in Alfalfa (Medicago sativa L.): I. Induction of Phenylpropanoid Biosynthesis and Hydrolytic Enzymes in Elicitor-Treated Cell Suspension Cultures. Plant Physiol. 1990 Feb;92(2):440–446. doi: 10.1104/pp.92.2.440. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Lamb C. J. trans-Cinnamic acid as a mediator of the light-stimulated increase in hydroxycinnamoyl-CoA: quinate hydroxycinnamoyl transferase. FEBS Lett. 1977 Mar 15;75(1):37–40. doi: 10.1016/0014-5793(77)80047-1. [DOI] [PubMed] [Google Scholar]
- Matern U., Heller W., Himmelspach K. Conformational changes of apigenin 7-O-(6-O-malonylglucoside), a vacuolar pigment from parsley, with solvent composition and proton concentration. Eur J Biochem. 1983 Jun 15;133(2):439–448. doi: 10.1111/j.1432-1033.1983.tb07483.x. [DOI] [PubMed] [Google Scholar]
- Pankhurst C. E., Biggs D. R. Sensitivity of Rhizobium to selected isoflavonoids. Can J Microbiol. 1980 Apr;26(4):542–545. doi: 10.1139/m80-092. [DOI] [PubMed] [Google Scholar]
- Spencer B. The non-academic environment. Biochem Soc Trans. 1990 Apr;18(2):162–166. doi: 10.1042/bst0180162. [DOI] [PubMed] [Google Scholar]