Abstract
Humic substances have been widely used as plant growth promoters to improve the yield of agricultural crops. However, the mechanisms underlying this effect remain unclear. Root soluble protein profiles in plants 11 days after planting and cultivated with and without humic acids (HA, 50 mg CL−1), were analyzed using the label-free quantitative proteomic approach. Cultivation of maize with HA resulted in higher fresh weight of roots than in untreated plants (control). Plants treated with HA showed increased number, diameter and length of roots. In the proteomics analysis, differences were detected in the following categories: energy metabolism, cytoskeleton, cellular transport, conformation and degradation of proteins, and DNA replication. Thirty-four proteins were significantly more abundant in the seedlings treated with HA, whereas only nine proteins were abundant in the control. The effects on root architecture, such as the induction of lateral roots and biomass increase were accompanied by changes in the energy metabolism-associated proteins. The results show that the main effect of HA is protective, mainly associated with increased expression of the 2-cys peroxidase, putative VHS/GAT, and glutathione proteins. Indeed, these proteins had the highest fold-difference. Overall, these results improve our understanding of the molecular mechanisms of HA-promoted plant growth.
Highlights
Humic substances (HS) are a major component of soil organic matter, acting as an essential link between various chemical, physical, and biological properties of soil
HS can be characterized as relatively small organic molecules that are loosely bound by intermolecular hydrophobic interactions[4] that are disrupted by organic acids
Proteins in some categories were found only in maize roots treated with Humic acids (HA), including those involved in cell proliferation and signal transduction
Summary
Humic substances (HS) are a major component of soil organic matter, acting as an essential link between various chemical, physical, and biological properties of soil. Humic acids (HA) are the components of HS that are formed by associations of predominantly hydrophobic compounds (polymethylene chains, fatty acids, phenolic and steroid compounds) that are stabilized at neutral pH by hydrophobic dispersive forces (van der Waals, π-π bonding, and CH–π bonding)[4] The conformations of these compounds increase in size as intermolecular hydrogen bonds form at lower pH values, until the point of flocculation[4]. A label-free quantitative proteomic approach was used to understand the molecular mechanisms underlying the effects of HA on total protein expression in the root. This methodology is a large-scale strategy for protein identification in complex mixtures that involves the pre-digestion of intact proteins followed by peptide separation, fragmentation in a mass spectrometer and database search
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