White lupin has developed a complex strategy to limit microbial degradation of secreted citrate required for phosphate acquisition.

White lupins (Lupinus albus L.) respond to phosphate deficiency by producing special root structures called cluster roots. These cluster roots secrete large amounts of carboxylates into the rhizosphere, mostly citrate and malate, which act as phosphate solubilizers and enable the plant to grow in soils with sparingly available phosphate.

Isoflavonoid exudation from white lupin roots is influenced by phosphate supply, root type and cluster-root stage.

The internal concentration of isoflavonoids in white lupin (Lupinus albus) cluster roots and the exudation of isoflavonoids by these roots were investigated with respect to the effects of phosphorus (P) supply, root type and cluster-root developmental stage. To identify and quantify the major isoflavonoids exuded by white lupin roots, we used high-pressure liquid chromatography (HPLC) coupled to electrospray ionization (ESI) in mass spectrometry (MS). The major exuded isoflavonoids were identified as genistein and hydroxygenistein and their corresponding mono- and diglucoside conjugates.

Rapid analysis of stilbenes and derivatives from downy mildew-infected grapevine leaves by liquid chromatography-atmospheric pressure photoionisation mass spectrometry.

Resveratrol, trans-epsilon-viniferin and trans-delta-viniferin are the major stilbenes induced in downy mildew infected grapevine leaves. In addition, nine minor polyphenolic compounds, described as stilbenes derivatives, have been separated and detected among known stilbenes after a methanolic microextraction of small pieces (1-2 mg) from infected grapevine leaves with a rapid, qualitative and optimized HPLC method coupled to mass spectrometry using atmospheric pressure photoionisation (APPI-MS(n)). The characterization of unknown stilbenic derivatives as six resveratrol dimers, two dimethylated resveratrol dimers and a resveratrol trimer are reported.

Delta-viniferin, a resveratrol dehydrodimer: one of the major stilbenes synthesized by stressed grapevine leaves.

Delta-viniferin is a resveratrol dehydrodimer, an isomer of epsilon-viniferin. This compound has been reported as a molecule produced in vitro by the oxidative dimerization of resveratrol by plant peroxidases or fungal laccases. It was also recently identified in wines and in grape cell cultures.

Differentiation of isomeric flavone/isoflavone aglycones by MS2 ion trap mass spectrometry and a double neutral loss of CO.

The fragmentation behaviour of seven pairs of isomeric flavone/isoflavone aglycones (solely hydroxylated and/or methoxylated) was studied using ion trap mass spectrometry with atmospheric pressure ionisation (API, both electrospray and APCI) in the positive and negative ion modes. A major difference was found in the neutral loss of 56 u, which was a common feature of all isoflavones in API(+). It was identified as a double loss of CO by accurate mass tandem mass spectrometric (MS/MS) measurements using a hybrid quadrupole time-of-flight (Q-TOF) instrument.