title: Nitrogen nutrition and the accumulation of free and sinapoyl-bound malic acid in Raphanus sativus cotyledons.
abstract: Seedlings of red radish (Raphanus sativus L. var. sativus) accumulated high amounts of free malic acid and sinapoylmalate, when grown on nitrate as the sole N-source. In the presence of ammonium (NO 3 (-) : NH 4 (+) , 1:2) both metabolites failed to accumulate, and the levels of arginine, asparagine, glutamine, histidine, and serine were greatly increased. The extractable activity of 1-sinapoylglucose: L-malate sinapoyltransferase, an enzyme which plays a key role in channelling malic acid into the sinapic-acid metabolism of this plant, was positively correlated with the malic-acid level in cotyledons. The possibility is discussed that free malic acid might be the likely candidate for regulating the activity of 1-sinapoylglucose: L-malate sinapoyltransferase.
authors.affiliation: Botanisches Institut der Universität Köln, Gyrhofstrasse 15, D-5000, Köln 41, Federal Republic of Germany.
authors.forename: B
authors.initials: B
authors.lastname: Dahlbender
authors.forename: D
authors.initials: D
authors.lastname: Strack