Stress Responses in Alfalfa (Medicago sativa L.)

Abstract

The isoflavonoid conjugates medicarpin-3-0-glucoside-6"-Omalonate (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 [14CJphenylalanine 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-a-aminooxy-,#-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.

Stress Responses in Alfalfa (Medicago sativa L.) (XIV. Changes in the Levels of Phenylpropanoid Pathway Intermediates in Relation to Regulation of L-Phenylalanine Ammonia-Lyase in Elicitor-Treated Cell-Suspension Cultures)

“…Previous studies have shown that treatment of elicited bean cultures with AOPP, a potent and specific inhibitor of PAL activity, and, therefore, CA production in vivo, results in increased accumulation of PAL transcripts and enzyme activity (Bolwell et al, 1988;Mavandad et al, 1990). However, levels of phenylpropanoid pathway intermediates were not measured in these studies, and no data are available conceming the effects of AOPP on PAL transcripts in alfalfa cultures, although the inhibitor has been shown to decrease the accumulation of medicarpin in these cells (Kessmann et al, 1990).…”

Comprehensive evaluation of phytoestrogen accumulation in plants and in vitro cultures of Medicago sativa L. ‘Elçi’ and natural tetraploid Trifolium pratense L.

“…Medicarpin, afrormosin glucoside, and afrormosin glucoside malonate were determined in cell suspension cultures of M. sativa L. 'Calwest 475' (Kessmann et al, 1990c). Twenty-seven isoflavones, flavone glucosides, and/ or glucoside malonates were determined in cell suspension cultures of M. truncatula L. (Farag et al, 2007).…”

“…These leguminous plants accumulate a wide range of phenolic secondary compounds, including isoflavonoid conjugates (Kessmann et al, 1990b). An important group of legume natural products, isoflavones, have been better understood at the molecular genetic level (Dixon et al, 1995;Dixon 1999;Dixon et al, 2004).…”

Metabolomics Reveals Novel Pathways and Differential Mechanistic and Elicitor-Specific Responses in Phenylpropanoid and Isoflavonoid Biosynthesis in Medicago truncatula Cell Cultures

“…Previous studies used targeted metabolite profiling to demonstrate that MeJA elicits the accumulation of triterpene saponins (Suzuki et al, 2002(Suzuki et al, , 2005Achnine et al, 2005), whereas YE, a pathogen mimic, induces the accumulation of both free and glycosylated isoflavonoids (Kessmann et al, 1990;Suzuki et al, 2005). The changes in primary metabolism in these elicited cell cultures have been described earlier (Broeckling et al, 2005), and a detailed analysis of transcript profiles will appear in a parallel article (Naoumkina et al, 2007).…”