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

Peats are an important reserve of humified carbon in terrestrial ecosystems. The interest in the use of humic substances as plant growth promoters is continuously increasing. The objective of this study was to evaluate the bioactivity of alkaline soluble humic substances (HS), humic (HA) and fulvic acids (FA) isolated from peats with different decomposition stages of organic matter (sapric, fibric and hemic) in the Serra do Espinhaço Meridional, state of Minas Gerais. Dose-response curves were established for the number of lateral roots growing from the main plant axis of tomato seedlings. The bioactivity of HA was greatest (highest response in lateral roots at lowest concentration) while FA did not intensify root growth. Both HS and HA stimulated root hair formation. At low concentrations, HS and HA induced root hair formation near the root cap, a typical hormonal imbalance effect in plants. Transgenic tomato with reporter gene DR5::GUS allowed the observation that the auxin-related signalling pathway was involved in root growth promotion by HA

Humic substances isolated from residues of sugar cane industry as root growth promoter Substâncias húmicas isoladas de resíduos da indústria da cana-de-açúcar como promotoras de crescimento radicular

Plant growth promoting substances are widely used in modern agriculture. Several products in the market are humic substances isolated from different sources. The filter cake, a residue of sugar production, is a rich and renewable source of organic matter and these characteristics place the filter cake as a possible source of plant growth promoting substances. Humic acids (HA) from filter cake were characterized, and their effects as root growth promoters were evaluated. Chemical features of the HA were evaluated through elemental composition, acidic functional groups, E4/E6 ratio and infrared spectroscopy analyzes. The biological activity of the HA was assessed using root architecture parameters and the P-type H+-ATPase activity. The lateral root development was directly related to the stimulation of plasma membrane ATPase activity. The ability of HA to promote root development indicate that HA from filter cake can be used as environmental plant growth stimulators.<br>Substâncias promotoras do crescimento vegetal são amplamente utilizadas na agricultura moderna. Existem vários produtos no mercado, muitos dos quais são substâncias húmicas isoladas de diferentes fontes. A torta de filtro, um resíduo da produção do açúcar, é uma fonte rica e renovável de matéria orgânica e essas características a tornam uma possível fonte de substâncias promotoras do crescimento vegetal. Ácidos húmicos (AH) da torta de filtro foram caracterizados, e foi avaliado seu efeito como promotor de crescimento radicular. As características químicas dos AH foram avaliadas por meio da composição elementar, grupos funcionais ácidos, relação E4/E6 e espectroscopia de infravermelho. A atividade biológica dos AH foi acessada avaliando-se a arquitetura radicular e a atividade da H+-ATPase de membrana plasmática. O desenvolvimento de raízes laterais foi diretamente relacionado ao estímulo da atividade da H+-ATPase. A habilidade dos AH em promover o desenvolvimento radicular indica que AH extraídos da torta de filtro podem ser utilizados como estimuladores do crescimento de plantas