Stress Responses in Alfalfa (Medicago sativa L.) : V. Constitutive and Elicitor-Induced Accumulation of Isoflavonoid Conjugates in Cell Suspension Cultures.

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 [(14)C]phenylalanine indicated that afrormosin conjugates were the major de novo synthesized isoflavonoid products in unelicited cells. During elicitation, [(14)C]phenylalanine was incorporated predominantly into medicarpin, although a significant proportion of the newly synthesized medicarpin was also conjugated. Treatment of (14)C-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.

[1]  Shinji Yata,et al.  A β-Hydroxychalcone and Flavonoids from Alfalfa Callus Stimulated by a Fungal Naphthoquinone, PO-1 , 1988 .

[2]  H. Kessmann,et al.  Elicitation of Pterocarpan Phytoalexins in Cell Suspension Cultures of Different Chickpea (Cicer arietinum L.) Cultivars by an Elicitor from the Fungus Ascochyta rabiéi , 1988 .

[3]  F. Fronczek,et al.  Isoflavones from an Insect-Resistant Variety of Soybean and the Molecular Structure of Afrormosin , 1986 .

[4]  R. Dixon,et al.  Differential biochemical effects of elicitor preparations from Colletotrichum lindemuthianum , 1986 .

[5]  L. Merlini,et al.  Analogs of phytoalexins. Synthesis of some 3-phenylcoumarins and their fungicidal activity , 1986 .

[6]  U. Matern,et al.  Conformational changes of apigenin 7-O-(6-O-malonylglucoside), a vacuolar pigment from parsley, with solvent composition and proton concentration. , 1983, European journal of biochemistry.

[7]  N. Farnsworth,et al.  Stevia rebaudiana: I. Use of p-bromophenacyl bromide to enhance ultraviolet detection of water-soluble organic acids (steviolbioside and rebaudioside B) in high-performance liquid chromatographic analysis , 1980 .

[8]  C. Pankhurst,et al.  Sensitivity of Rhizobium to selected isoflavonoids. , 1980, Canadian journal of microbiology.

[9]  C. Lamb.  trans‐Cinnamic acid as a mediator of the light‐stimulated increase in hydroxycinnamoyl‐CoA: Quinate hydroxycinnamoyl transferase , 1977, FEBS letters.

[10]  T. Mabry,et al.  The Systematic Identification of Flavonoids , 1970, Springer Berlin Heidelberg.

[11]  D. Dornbos,et al.  Medicarpin Delays Alfalfa Seed Germination and Seedling Growth , 1990 .

[12]  T. L. Graham,et al.  Role of constitutive isoflavone conjugates in the accumulation of glyceollin in soybean infected with Phytophthora megasperma. , 1990 .

[13]  R. Dixon,et al.  Metabolic fate of cinnamic acid in elicitor treated cell suspension cultures of Phaseolus vulgaris. , 1990 .

[14]  Wolfgang G. W. Kurz,et al.  Primary and Secondary Metabolism of Plant Cell Cultures II , 1989, Springer Berlin Heidelberg.

[15]  H. Kessmann,et al.  Elicitation and Suppression of Isoflavones and Pterocarpan Phytoalexins in Chickpea (Cicer arietinum L.) Cell Cultures , 1989 .

[16]  G. Bringmann,et al.  In vivo characterization of NADPH: 2'-hydroxyisoflavone oxidoreductase in elicitor treated chickpea cell cultures and stereochemical aspects of the phytoalexins medicarpin and maackiain , 1988 .

[17]  W. Barz,et al.  Differential turnover of isoflavone 7-O-glucoside-6″-O-malonates in Cicer arietinum roots , 1985 .

[18]  P. Dewick,et al.  Biosynthesis of pterocarpan and isoflavan phytoalexins in Medicago sativa: the biochemical interconversion of pterocarpans and 2′-hydroxyisoflavans , 1979 .