Cell wall‐associated isoflavonoids andβ‐glucosidase activity inLupinus albusplants responding to environmental stimuli

Abstract

Plants respond to various biotic or abiotic stimuli with different mechanisms and the mobilization of phenolic compounds is one of them. In white lupin ( Lupinus albus L.) plants, isoflavones and their glucosides were localized in cell walls where the high constitutive activity of β β β β -glucosidase (EC 3·2·1·21) was also identified. The enzyme was partially purified from root cell walls. Its polymeric active form has 180 or 200 kDa as determined by non-denaturing electrophoresis and gel filtration, respectively, and the isoelectric point is at pH 6·9. The enzyme is an exoglucosidase, preferentially hydrolysing conjugates of phenolic compounds with β β β β anomers of glucose. It is not active against purified lupin cell walls. The specific β β β β -glucosidase activity varies in different tissues with the highest one in roots, and always higher in cell walls than in protoplast. The cell wall location of the enzyme was confirmed biochemically by its activity in intercellular washing fluids. Both aglycones and glycosides were also present in these fluids. The specific β β β β -glucosidase activity correlated well with the isoflavonoid aglycone/glycoside ratios in various tissues: the higher β β β β -glucosidase activity, the higher relative aglycone content. β β β β -glucosidase activity was found to be inducible under conditions of yeast elicitor treatment. Induction of the enzyme was accompanied by changes in the isoflavone secretion and accumulation, suggesting the regulatory role of β β β β -glucosidase activity in root exudation of isoflavonoids. No correlation however, was found between changes in β β β β -glucosidase activity and the presence of isoflavonoids in root exudates of plants grown under various nitrogen nutrition regimes.

Influence of abiotic stress during soybean germination followed by recovery on the phenolic compounds of radicles and their antioxidant capacity

“…The content of all identified isoflavones increased in all stress-treated samples, which confirms previously published data [26,33,37,38]. Wu [39] demonstrated that soybean isoflavones show free radical scavenging potential, with aglycones (daidzein and genistein) being stronger scavengers than their glycoside conjugates (daizdin and genistin).…”

Changes in rutin concentration and flavonol-3-glucosidase activity during seedling growth in tartary buckwheat (Fagopyrum tataricum Gaertn.)

“…To date, there are several reports of studies of flavonoid-glucoside in the root (Shibuya et al 1991). In addition, conjugated flavonoid-glucosidase activity was reported in lupin root (Pislewska et al 2002). However, these reports are of root nodule plants.…”

Different mechanisms for phytoalexin induction by pathogen and wound signals in Medicago truncatula

“…G2 preferred isoflavonoid over flavonoid glucosides, and G4, with a broad substrate preference, was down-regulated by YE. Other ␤-glucosidases have been shown to exhibit preference for specific (iso)flavonoid compounds, such as a set of chickpea isoenzymes possessing K m values for isoflavones of at least 100-fold lower than for other phenolic glycosides (34), enzymes from white lupin roots that, like the Medicago enzymes, can cleave isoflavone glucosides but not kaempferol 3-O-␤-glucoside (35), and an enzyme from soybean roots (GmICHG) that has very high specificity and turnover for gensitein and daidzein malonyl glucosides (36). This enzyme is found in the cell wall fraction in soybean roots, and, of the Medicago enzymes reported here, is most closely related to G2 (70% at the amino acid level) (SI Fig.…”