Bioactivity of chemically transformed humic matter from vermicompost on plant root growth.
Chemical reactions (hydrolysis, oxidation, reduction, methylation, alkyl compounds detachment) were applied to modify the structure of humic substances (HS) isolated from vermicompost. Structural and conformational changes of these humic derivatives were assessed by elemental analyses, size exclusion chromatography (HPSEC), solid-state nuclear magnetic resonance ((13)C CPMAS-NMR), and diffusion ordered spectroscopy (DOSY-NMR), whereas their bioactivity was evaluated by changes in root architecture and proton pump activation of tomato and maize. All humic derivatives exhibited a large bioactivity compared to original HS, both KMnO(4)-oxidized and methylated materials being the most effective. Whereas no general relationship was found between bioactivity and humic molecular sizes, the hydrophobicity index was significantly related with proton pump stimulation. It is suggested that the hydrophobic domain can preserve bioactive molecules such as auxins in the humic matter. In contact with root-exuded organic acids the hydrophobic weak forces could be disrupted, releasing bioactive compounds from humic aggregates. These findings were further supported by the fact that HS and all derivatives used in this study activated the auxin synthetic reporter DR5::GUS.
Núcleo de Desenvolvimento de Insumos Biológicos para Agricultura (NUDIBA), Universidade Estadual do Norte Fluminense Darcy Ribeiro (UENF), Av. Alberto Lamego 2000, Campos dos Goytacazes, Rio de Janeiro, Brazil.
Leonardo Barros
LB
Dobbss
Luciano
L
Pasqualoto Canellas
Fábio
F
Lopes Olivares
Natália
N
Oliveira Aguiar
Lázaro Eustáquio Pereira
LE
Peres
Mariana
M
Azevedo
Riccardo
R
Spaccini
Alessandro
A
Piccolo
Arnoldo R
AR
Façanha
D006812:Humic Substances / Q000032:analysis*; D063245:Plant Development; D018517:Plant Roots / Q000254:growth & development*; D012987:Soil / Q000032:analysis*
D006812:Humic Substances; D012987:Soil