Plant Physiol, December 2002, Vol. 130, pp. 1951-1957

Humic Acids Isolated from Earthworm Compost Enhance Root Elongation, Lateral Root Emergence, and Plasma Membrane H⁺-ATPase Activity in Maize Roots¹

Centro de Ciências Tecnologias Agropecuárias, Laboratório de Solos (L.P.C.), Centro de Biociências Biotecnologia, Laboratório de Biologia Celular e Tecidual (F.L.O., A.R.F.), and Laboratório de Fisiologia Bioquímica de Microrganismos (A.L.O.-F.), Universidade Estadual do Norte Fluminense, Avenida Alberto Lamego, 2000, CEP 28015-620, Campos dos Goytacazes, Rio de Janeiro, Brazil

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⁺-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⁺-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.