Abstract
The effect of a low-molecular weight, water-extractable fraction of humic substances (WEHS) derived from sphagnum peat on post-embryonic plant development has been studied using Arabidopsis roots. Application of humic substances caused an array of changes in root morphology, such as an increase in root hair length and density, formation of ectopic root hairs, and an increase in cell proliferation in the root ground tissue. Application of WEHS affected genes involved in epidermal cell fate specification, suggesting that humic substances can alter developmental programs at an early stage of root cell differentiation. The WEREWOLF and GLABRA2 genes, encoding negative regulators of the root hair cell fate, were significantly down-regulated in the presence of WEHS. Thus, the presence of humic substances caused an ordered remodeling of the root morphology, leading to an increased absorptive surface of the root. Growth in the presence of WEHS did not rescue the phenotype of the root hair defective rhd6 mutant. Analyzing BA3:uidA and DR5:uidA transgenic plants, carrying auxin response elements, and monitoring the expression of the auxin-responsive GH3 gene by real-time RT-PCR did not provide evidence for a WEHS-induced expression of auxin-related genes. It is concluded that WEHS do not exert their effects in an auxin-like manner.
Similar content being viewed by others
References
Aiken GR, Thurman EM, Malcolm RL (1979) Comparison of XAD macroporous resins for the concentration of fulvic acid from aqueous solution. Anal Chem 51:1799–1803
Altschul SF, Madden TL, Schaffer AA, Zhang J, Zhang Z, Miller W, Lipman DJ (1997) Gapped BLAST and PSI-BLAST: a new generation of protein database search programs. Nucleic Acids Res 25:3389–3402
Bernhardt C, Zhao M, Gonzalez A, Lloyd A, Schiefelbein J (2005) The bHLH genes GL3 and EGL3 participate in an intercellular regulatory circuit that controls cell patterning in the Arabidopsis root epidermis. Dev 132:291–298
Canellas LP, Olivares FL, Okorokova-Façanha AL, Rocha Façanha AR (2002) Humic acids isolated from earthworm compost enhance root elongation, lateral root emergence, and plasma membrane H+-ATPase activity in maize roots. Plant Physiol 130:1951–1957
Chen Y, Magen H, Riov J (1994) Humic substances originating from rapidly decomposing organic matter: properties and effects on plant growth. In: Senesi N, Miano TM (eds) Humic substances in the global environment and implication on human health. Elsevier, Amsterdam, The Netherlands, pp 427–443
Concheri G, Nardi S, Reniero F, Dell’Agnola G (1996) The effects of humic substances within the Ah horizon of a calcic luvisol on morphological changes related to invertase and peroxidases activities in wheat roots. Plant Soil 179:65–73
Dolan L (2006) Positional information and mobile transcriptional regulators determine cell pattern in the Arabidopsis root epidermis. J Exp Bot 57:51–54
Estelle MA, Somerville C (1987) Auxin-resistant mutants of Arabidopsis thaliana with an altered morphology. Mol Gen Genet 206:200–206
Gerke J (1997) Aluminium and iron (III) species in the soil solution including organic complexes with citrate and humic substances. Z Pflanzenernär Bodenk 160:427–432
Hagen G, Guilfoyle TJ (1985) Rapid induction of selective transcription by auxins. Mol Cell Biol 5:1197–1203
Kurata T, Ishida T, Kawabata-Awai C, Noguchi M, Hattori S, Sano R, Nagasaka R, Tominaga R, Koshino-Kimura Y, Kato T, Sato S, Tabata S, Okada K, Wada T (2005) Cell-to-cell movement of the CAPRICE protein in Arabidopsis root epidermal cell differentiation. Dev 132:5387–5398
Kwak SH, Shen R, Schiefelbein J (2005) Positional signaling mediated by a receptor-like kinase in Arabidopsis. Science 307:1111–1113
Ma Z, Bielenberg DG, Brown KM, Lynch JP (2001) Regulation of root hair density by phosphorus availability in Arabidopsis thaliana. Plant Cell Envir 24:459–467
Masucci JD, Schiefelbein JW (1996) Hormones act downstream of TTG and GL2 to promote root hair outgrowth during epidermis development in the Arabidopsis root. Plant Cell 8:1505–1517
Menand B, Yi K, Jouannic S, Hoffmann L, Ryan E, Linstead P, Schaefer DG, Dolan L (2007) An ancient mechanism controls the development of cells with a rooting function in land plants. Science 316:1477–1480
Müller M, Schmidt W (2004) Environmentally induced plasticity of root hair development in Arabidopsis. Plant Physiol 134:409–419
Muscolo A, Cutrupi S, Nardi S (1998) IAA detection in humic substances. Soil Biol Biochem 30:199–201
Narang RA, Bruene A, Altmann T (2000) Analysis of phosphate acquisition efficiency in different Arabidopsis accessions. Plant Physiol 124:1786–1799
Nardi S, Pizzeghello D, Muscolo A, Vianello A (2002) Physiological effects of humic substances on higher plants. Soil Biol Biochem 34:1527–1536
Oono Y, Chen QG, Overvoorde PJ, Köhler C, Theologis A (1998) Age mutants of Arabidopsis exhibit altered auxin-regulated gene expression. Plant Cell 10:1649–1662
Pfaffl MW (2001) A new mathematical model for relative quantification in real-time RT-PCR. Nucleic Acids Res 29:2002–2007
Pinton R, Cesco S, De Nobili M, Santi S, Varanini Z (1998) Water and pyrophosphate-extractable humic substances fractions as a source of iron for Fe-deficient cucumber plants. Biol Fertil Soils 26:23–27
Pinton R, Cesco S, Iacolettig G, Astolfi S, Varanini Z (1999a) Modulation of NO3 uptake by water-extractable humic substances: involvement of root plasma membrane H+ATPase. Plant Soil 215:155–161
Pinton R, Cesco S, Santi S, Agnolon F, Varanini Z (1999b) Water-extractable humic substances enhance iron deficiency responses by Fe-deficient cucumber plants. Plant Soil 210:145–157
Pizzeghello D, Nicolini G, Nardi S (2000) Hormone-like activity of humic substances in Fagus sylvaticae forests. New Phytol 151:647–657
Quaggiotti S, Ruperti B, Pizzeghello D, Francioso O, Tugnoli V, Nardi S (2004) Effect of low molecular size humic substances on nitrate uptake and expression of genes involved in nitrate transport in maize. J Exp Bot 55:803–813
Rozen S, Skaletsky HJ (2000) Primer3 on the WWW for general users and for biologist programmers. In: Krawetz S, Misener S (eds) Bioinformatics methods and protocols: methods in molecular biology. Humana, Totowa, NJ, pp 365–386
Ryu KH, Kang YH, Park YH, Hwang I, Schiefelbein J, Lee MM (2005) The WEREWOLF MYB protein directly regulates CAPRICE transcription during cell fate specification in the Arabidopsis root epidermis. Dev 132:4765–4775
Schmidt W, Schikora A (2001) Different pathways are involved in phosphate and iron stress-induced alterations of root epidermal cell development. Plant Physiol 125:2078–2084
Ulmasov T, Murfett J, Hagen G, Guilfoyle T (1997) Aux/IAA proteins repress expression of reporter genes containing natural and highly active synthetic auxin response elements. Plant Cell 9:1963–1971
Varanini Z, Pinton R (2000) Direct versus indirect effects of soil humic substances on plant growth and nutrition. In: Pinton R, Varanini Z, Nannipieri P (eds) The Rhizosphere. Marcel Dekker, New York, pp 141–157
Vaughan D, Malcolm RE (1985) Influence of humic substances on growth and physiological process. In: Vaughan D, Malcolm RE (eds) Soil organic matter and biological activity. Kluwer Academic Publishers, Dordrecht, The Netherlands, pp 37–75
Acknowledgments
We thank Dr. Paula Perry for professional help in minor (plant) surgery.
Author information
Authors and Affiliations
Corresponding author
Additional information
Responsible Editor: Jian Feng Ma.
Rights and permissions
About this article
Cite this article
Schmidt, W., Santi, S., Pinton, R. et al. Water-extractable humic substances alter root development and epidermal cell pattern in Arabidopsis . Plant Soil 300, 259–267 (2007). https://doi.org/10.1007/s11104-007-9411-5
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s11104-007-9411-5