title: The root application of a purified leonardite humic acid modifies the transcriptional regulation of the main physiological root responses to Fe deficiency in Fe-sufficient cucumber plants.
abstract: The aim of this study is to investigate the effect of a well-characterized purified humic acid (non-measurable concentrations of the main plant hormones were detected) on the transcriptional regulation of the principal molecular agents involved in iron assimilation. To this end, non-deficient cucumber plants were treated with different concentrations of a purified humic acid (PHA) (2, 5, 100 and 250 mg of organic carbonL(-1)) and harvested 4, 24, 48, 76 and 92 h from the onset of the treatment. At harvest times, the mRNA transcript accumulation of CsFRO1 encoding for Fe(III) chelate-reductase (EC 1.16.1.7); CsHa1 and CsHa2 encoding for plasma membrane H+-ATPase (EC 3.6.3.6); and CsIRT1 encoding for Fe(II) high-affinity transporter, was quantified by real-time RT-PCR. Meanwhile, the respective enzyme activity of the Fe(III) chelate-reductase and plasma membrane H+-ATPase was also investigated. The results obtained indicated that PHA root treatments affected the regulation of the expression of the studied genes, but this effect was transient and differed (up-regulation or down-regulation) depending on the genes studied. Thus, principally the higher doses of PHA caused a transient increase in the expression of the CsHa2 isoform for 24 and 48 h whereas the CsHa1 isoform was unaffected or down-regulated. These effects were accompanied by an increase in the plasma membrane H+-ATPase activity for 4, 48 and 96 h. Likewise, PHA root treatments (principally the higher doses) up-regulated CsFRO1 and CsIRT1 expression for 48 and 72 h; whereas these genes were down-regulated by PHA for 96 h. These effects were associated with an increase in the Fe(III) chelate-reductase activity for 72 h. These effects were not associated with a significant decrease in the Fe root or leaf concentrations, although an eventual effect on the Fe root assimilation pattern cannot be ruled out. These results stress the close relationships between the effects of humic substances on plant development and iron nutrition. However, further studies are needed in order to elucidate if these effects at molecular level are caused by mechanisms involving hormone-like actions and/or nutritional factors.
authors.affiliation: CIPAV (Centro de Investigación en Producción Animal y Vegetal), Timac Agro Int-Roullier Group, Polígono Arazuri-Orcoyen, Calle C n Degrees 32, 31160 Orcoyen, Spain.
authors.forename: Elena
authors.initials: E
authors.lastname: Aguirre
authors.forename: Aguirre
authors.initials: A
authors.lastname: Elena
authors.forename: Diane
authors.initials: D
authors.lastname: Leménager
authors.forename: Leménager
authors.initials: L
authors.lastname: Diane
authors.forename: Eva
authors.initials: E
authors.lastname: Bacaicoa
authors.forename: Bacaicoa
authors.initials: B
authors.lastname: Eva
authors.forename: Marta
authors.initials: M
authors.lastname: Fuentes
authors.forename: Fuentes
authors.initials: F
authors.lastname: Marta
authors.forename: Roberto
authors.initials: R
authors.lastname: Baigorri
authors.forename: Baigorri
authors.initials: B
authors.lastname: Roberto
authors.forename: Angel Ma
authors.initials: AM
authors.lastname: Zamarreño
authors.forename: José Ma
authors.initials: JM
authors.lastname: García-Mina
mesh_terms: D001483:Base Sequence; D002851:Chromatography, High Pressure Liquid; D018553:Cucumis sativus / Q000235:genetics / Q000502:physiology*; D017931:DNA Primers; D018506:Gene Expression Regulation, Plant / Q000187:drug effects*; D017343:Genes, Plant; D006812:Humic Substances; D007501:Iron / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy; D018517:Plant Roots / Q000502:physiology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D053719:Tandem Mass Spectrometry; D014158:Transcription, Genetic / Q000187:drug effects*
chemical_list: D017931:DNA Primers; D006812:Humic Substances; D007501:Iron