title: Action of humic acid on promotion of cucumber shoot growth involves nitrate-related changes associated with the root-to-shoot distribution of cytokinins, polyamines and mineral nutrients.
abstract: Numerous studies have reported the ability of humic substances to increase shoot growth in different plant species cultivated under diverse growth conditions. However, the mechanism responsible for this effect of humic substances is poorly understood. It is possible that the shoot promoting effect of humic substances involves a primary effect on root H(+)-ATPase activity and nitrate root-shoot distribution that, in turn, causes changes in the root-shoot distribution of certain cytokinins, polyamines and abscisic acid, thus affecting shoot growth. We investigated this hypothesis in the present study. The results showed that the root application of a purified humic acid causes a significant increase in shoot growth that is associated with an enhancement in root H(+)-ATPase activity, an increase in nitrate shoot concentration, and a decrease in roots. These effects were associated with significant increases in the shoot concentration of several cytokinins and polyamines (principally putrescine), concomitant with decreases in roots. Likewise, these changes in the root-shoot distribution of diverse active cytokinins correlated well to significant changes in the root-shoot distribution of several mineral nutrients. These results, taken together, indicate that the beneficial effects of humic substances on shoot development in cucumber could be directly associated with nitrate-related effects on the shoot concentration of several active cytokinins and polyamines (principally putrescine).
authors.affiliation: Department of Chemistry and Soil Chemistry, Faculty of Sciences, University of Navarra, P.O. Box 273, 31080 Pamplona (Navarra), Spain.
authors.forename: Verónica
authors.initials: V
authors.lastname: Mora
authors.forename: Eva
authors.initials: E
authors.lastname: Bacaicoa
authors.forename: Angel-Maria
authors.initials: AM
authors.lastname: Zamarreño
authors.forename: Elena
authors.initials: E
authors.lastname: Aguirre
authors.forename: Maria
authors.initials: M
authors.lastname: Garnica
authors.forename: Marta
authors.initials: M
authors.lastname: Fuentes
authors.forename: José-Maria
authors.initials: JM
authors.lastname: García-Mina
mesh_terms: D000040:Abscisic Acid / Q000378:metabolism; D018533:Biomass; D002462:Cell Membrane / Q000201:enzymology; D018553:Cucumis sativus / Q000254:growth & development* / Q000378:metabolism; D003583:Cytokinins / Q000378:metabolism*; D004602:Elements; D006812:Humic Substances / Q000032:analysis*; D009682:Magnetic Resonance Spectroscopy; D008903:Minerals / Q000378:metabolism*; D008970:Molecular Weight; D050901:Nitrate Reductase / Q000378:metabolism; D009566:Nitrates / Q000378:metabolism; D018515:Plant Leaves / Q000378:metabolism; D018517:Plant Roots / Q000201:enzymology / Q000378:metabolism*; D018520:Plant Shoots / Q000201:enzymology / Q000254:growth & development* / Q000378:metabolism; D011073:Polyamines / Q000378:metabolism*; D006180:Proton-Translocating ATPases / Q000378:metabolism
chemical_list: D003583:Cytokinins; D004602:Elements; D006812:Humic Substances; D008903:Minerals; D009566:Nitrates; D011073:Polyamines; D000040:Abscisic Acid; D050901:Nitrate Reductase; D006180:Proton-Translocating ATPases