Humic acids crossinteractions with root and organic acids

Abstract

The apparent high molecular mass of humic acids (HAs) hardly seems compatible with their direct effects in plant physiology. However, previous evidence has indicated that HAs are non-covalent associations of relatively small molecules, which can be broken down by the action of organic acids. The aim of this work was to evaluate the effects of organic acids on the structure of HAs by spectroscopy and on their bioactivity by following the responses of maize root growth. Changes in the exudation of organic acids from maize seedlings treated with HAs at 50 mg C L 21 were evaluated by high-performance liquid chromatography. The results are in agreement with the concept that HAs are chemical aggregates that acquire characteristics typical of low-molecular-mass humic substances when exposed to organic acids exuded by the roots. Maize seedlings grown in solutions supplemented with HAs plus citric acid at 0.0005, 0.005 and 0.05 mM exhibited significant changes in their root area, primary root length, number of lateral roots and lateral root density and increases in plasma membrane H + -ATPase activity. Furthermore, the root exudation profile of plants treated with HAs exhibited an increase in the efflux of oxalic and citric acids, with a concurrent decrease in malic and succinic acids. These data reveal a crosstalk between HAs and plants where the exudation of organic acids from the roots influences and is influenced by bioactive molecules released from HAs during root development.

Root growth of tomato seedlings intensified by humic substances from peat bogs

“…Em solução, os AH podem liberar parte de seus componentes com a adição de pequenas quantidades de ácidos orgânicos (Piccolo et al, 1999;Cozzolino et al, 2001) tais como os exsudados pelas raízes. Além disso, Canellas et al (2008b) …”

Desempenho do abacaxizeiro 'Vitória' em resposta à aplicação de ácidos húmicos durante a aclimatação

“…Se, por um lado, a alteração da propriedade de permeabilidade seletiva da plasmalema em tese pode aumentar a entrada de íons, por outro pode favorecer também a saída, uma vez que a ação surfactante não preserva a seletividade das membranas (Nardi et al, 2002). Canellas et al (2008) verificaram que plântulas de milho, tratadas com AHv, modificam o seu perfil de exsudação radicular de ácidos orgânicos, aumentando, significativamente, a extrusão de ácido cítrico e oxálico. Em contato com o ambiente acidificado da rizosfera, as partículas supraestruturais dos ácidos húmicos podem se fragmentar e gerar subunidades potencialmente capazes de alterar o metabolismo celular, por meio da ativação de H + -ATPases da membrana plasmática de células de raiz (Piccolo, 2001;Façanha et al, 2002;Canellas et al, 2006).…”

Humic substances, purified MAP and hydrogel in the development and survival of Eucalyptus urograndis

“…According to Canellas et al (2008), humic substances have auxinic action. This is in agreement with Silva et al (2011), who reported, as the main physiological effect, the increase in root development, according to the species, plant age, source and concentration.…”

“…Zandonadi & Busato (2012) and Zandonadi et al (2013; cite that humic substances can activate root and leaf development, increase in the absorption of nutrients and regulation of enzymes that govern plant metabolism, such as H + -ATPase and nitrate-reductase, and protons pumps are essential for the absorption of nutrients by plants. Canellas et al (2008) also described the occurrence of an auxinic action present in the humic substance.…”