Role of Nitrogen and Plant Growth Regulators in the Exudation and Accumulation of lsoflavonoids by Roots of Intact White (Lupin ( Lupinus albus L.) Plants

Abstract

Summary Two isoflavonoid glycosides (7-O-β-glucopyranosides of 2′-hydroxygenistein and genistein) and up to six aglycones (2′-hydroxygenistein, genistein, wighteone, luteone, lupinisoflavone A, parvisoflavone B) were identified in root exudates and/or root extracts from white lupin ( Lupinus albus L. cv. Bac) plants. Three-d-old seedlings were cultivated for 14d on 1/2 Knop's nutrient solutions. Various treatments, differing in the form (No 3 − , NH 4 + , NH 4 N0 3 , urea) and concentration of nitrogen, and the presence of plant growth regulators in the medium were tested. Nitrogen, in all forms applied, affects both the exudation and accumulation of phenolics with the inhibitory activites arranged in the order: N0 3 − > NH 4 N0 3 > urea > NH 4 + . With higher concentration of N in the medium, the exudation of phenolics decreases. Processes of isoflavone exudation and accumulation respond differentially to nitrogen status. Exogenously applied plant growth regulators modify inhibitory effects of nitrate on the exudation and accumulation of isoflavones. Their activity depend on the type of growth regulator used (NAA, BAP, GA 3 ), its chemical structure (IAA, IBA, NAA) and concentration in the medium. Lupin isoflavones might be potential signals in legume — Rhizobium interactions. These data show a correlation between plant nutrient status and the accumulation and exudation of putative phenolic signal molecules, thus indicating the existence of possible additional controls in the regulation of nodulation process.