Earthworms (Eisenia foetida) produce humic substances that can influence plant growth by mechanisms that are not yet clear. In this work, we investigated the effects of humic acids (HAs) isolated from cattle manure earthworm compost on the earliest stages of lateral root development and on the plasma membrane H ϩ -ATPase activity. These HAs enhance the root growth of maize (Zea mays) seedlings in conjunction with a marked proliferation of sites of lateral root emergence. They also stimulate the plasma membrane H ϩ -ATPase activity, apparently associated with an ability to promote expression of this enzyme. In addition, structural analysis reveals the presence of exchangeable auxin groups in the macrostructure of the earthworm compost HA. These results may shed light on the hormonal activity that has been postulated for these humic substances.

Increasing evidences have indicated that humic substances can induce plant growth and productivity by functioning as an environmental source of auxinic activity. Here we comparatively evaluate the effects of indole-3-acetic acid (IAA) and humic acids (HA) isolated from two different soils (Inseptsol and Ultisol) and two different organic residues (vermicompost and sewage sludge) on root development and on activities of plasmalemma and tonoplast H(+ )pumps from maize roots. The data show that HA isolated from these different sources as well as low IAA concentrations (10(-10) and 10(-15) M) improve root growth through a markedly proliferation of lateral roots along with a differential activation not only of the plasmalemma but also of vacuolar H(+)-ATPases and H(+)-pyrophosphatase. Further, the vacuolar H(+)-ATPase had a peak of stimulation in a range from 10(-8) to 10(-10) M IAA, whereas the H(+)-pyrophosphatase was sensitive to a much broader range of IAA concentrations from 10(-3) to 10(-15) M. It is proposed a complementary view of the acid growth mechanism in which a concerted activation of the plasmalemma and tonoplast H(+ )pumps plays a key role in the root cell expansion process driven by environment-derived molecules endowed with auxinic activity, such as that of humic substances.

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High-external input agriculture is one of the most disruptive human activities, which have been justified by the current economic paradigm due to high productivity and the need to feed a growing population. However, we are dangerously close to the edge of the planet resources and both hunger and food insecurity has increased. Limiting the use of non-renewable chemical fertilizers and pesticides, changing water management, enhancing diversity and considering the often-neglected social dimension of agriculture are the bases to other chemical and biological technologies to agriculture. Biological inputs can stimulate the substitution of chemical inputs without questioning the current fundaments or can be adopted as a turning point to intensify the harsh processes of transition to more environmental friendly agriculture. The debate is open and our contribution is to develop the scientific basis for biological inputs that, unlike soluble fertilizers and pesticides, depend on a number of factors for its success in promoting crop yield. In this review, we showed the results obtained with the combined use of diazotrophic endophytic bacteria and humic substances in diverse crops (sugarcane, maize, tomato, common beans and pineapple), presenting the main morphological and physiological changes induced by biological technology. A snapshot of the state of the art of the use of plant growth promoting bacteria together with humic substances was provided, showing their potential especially when plants are subjected to moderate to severe abiotic stress. The number of studies reporting the combined use of plant growth promoting bacteria and humic substances is surprisingly low. There is an open avenue for research and encouraging debate is the goal. To overcome the conventional agriculture, maintaining productivity levels is more than scientific challenge, is a humanitarian duty. The biological inputs can help in this purpose.

(6) RESUMO A aclimatação de mudas de abacaxizeiro propagadas por cultura in vitro é um processo lento. A promoção do crescimento radicular pelo uso de ácidos húmicos pode ser útil durante esse processo. O objetivo deste trabalho foi avaliar o desempenho do abacaxizeiro 'Vitória' propagado por cultura de tecidos em resposta à aplicação de diferentes doses de ácidos húmicos isolados de vermicomposto e de torta de filtro durante o período de aclimatação em casa de vegetação. Foram avaliadas as características anatômicas da lâmina foliar, o teor de pigmentos fotossintéticos, o crescimento da parte aérea e do sistema radicular, e o conteúdo de nutrientes foliares. Os resultados mostraram incrementos no crescimento e desenvolvimento da parte aérea e do sistema radicular com a aplicação de ácidos húmicos, bem como acúmulo significativo de N, P, K, Ca e Mg e aumento na relação clorofila a/clorofila b. A promoção do crescimento das mudas durante o período de aclimatação, em resposta à aplicação de ácidos húmicos, pode melhorar a adaptação do abacaxizeiro ao ambiente ex vitro. Termos de indexação:Ananas comosus, cultura de tecidos, substâncias húmicas, nutrição mineral, bioatividade.(1) Parte da Tese de Doutorado da primeira autora. Recebido para publicação em dezembro de 2008 e aprovado em maio de 2009.

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Resumo -A bioatividade de ácidos húmicos (AH) isolados de lodo da estação de tratamento de esgoto (AHL) e de vermicomposto (AHV) foi avaliada pela ação dessas substâncias sobre o transporte de prótons através da membrana plasmática de células de raízes de café e milho e sua relação com o desenvolvimento dessas espécies. Houve estímulo da área superficial radicular em ambas as espécies cultivadas com ambos AH, mostrando uma concentração ótima em torno de 40 mg L -1 . Nessa condição, os tratamentos com AHL e AHV estimularam a H + -ATPase de membrana plasmática em plântulas de café e milho. Os AHL foram mais efetivos na promoção desses efeitos do que os AHV. A modificação do perfil cromatográfico dos AH em solução antes e após o cultivo das plântulas revelou que a interação planta-AH promoveu uma redistribuição das massas moleculares dessas substâncias, sugerindo uma dinâmica de mobilização de subunidades funcionais dos AH por exsudatos das raízes. A análise estrutural dos AH detectou a presença de grupamentos de auxina. A análise comparativa da ação desses dois AH sobre as espécies representantes de plantas monocotiledôneas (milho) e dicotiledôneas (café) apontam para a ativação da H + -ATPase de plasmalema como possível marcador metabólico de bioatividade dos ácidos húmicos.Termos para indexação: Zea mays, Coffea arabica, lodo residual, ácidos orgânicos, vermicomposto. Humic acids bioactivity: effects on root development and on the plasma membrane proton pumpAbstract -The bioactivity of humic acids (HA) isolated from sludge of the station of sewer treatment (HAL) and from vermicompost (HAV) was evaluated through the action of those substances on primary transport of protons of the plasma membrane of coffee and corn root cells and its relationship with the development of those species. A stimulation in the superficial area of roots was observed for both species cultivated with both humic acids, exhibiting an optimum concentration, about 40 mg L -1 of HA. In this condition the treatment with HAL and HAV stimulated the plasma membrane H + -ATPase of corn and coffee roots. HAL were more effective to promote those effects than HAV. The modification of the chromatographic profile of the HA in solution before and after the cultivation of the seedlings revealed that the interaction plant-HA promoted a rearrangement of the average molecular weight of those substances suggesting a dynamic mobilization of bioactive subunits of the HA by plant exudates. The structural analysis of the HA has detected the presence of auxin groups. A comparative analysis of the action of those HA on the monocotyledonous (corn) and dicotyledonous (coffee) plants indicates to the activation of plasmallema H + -ATPase as a possible metabolic marker for bioactivity of humic acids.