Acceso usuarios
The mechanisms by which the active compounds of Brachiaria ruziziensis R. Germ & C.M. Evrard are phytotoxic to the weed species Euphorbia heterophylla L. were examined. The respiratory activities of root apices and isolated mitochondria, the activities of antioxidant enzymes and the morphology of roots under the influence of exogenous phytohormones were evaluated. The effects of the butanolic fraction (BF) from B. ruziziensis were tested at 250 to 1000 µg mL-1. The BF stimulated the respiratory activity of roots, partially due to an increment in the alternate oxidase pathways. In isolated mitochondria the BF inhibited the respiration coupled to ADP phosphorylation. The activity of catalase and glutathione reductase in roots were higher than in the control condition, but in contrast, the activities of superoxide dismutase, ascorbate peroxidase, glutathione peroxidase and peroxidase were reduced. The roots of E. heterophylla grown in the presence of 1000 µg mL-1 were wider and shorter than those of controls. There was also an enhanced root hair development. Exogenous application of 8 nM indole acetic acid and 8 nM naftal acetic acid did not rescue the normal characteristics of roots. Abscisic acid (ABA) at 0.1 µM concentration caused similar changes to those ones caused by the BF. Cyto-histological observations of the longitudinal sections of roots showed reduction in the root cap region and an increased in the elongation zone. The whole of the data suggested that an elevation of ABA content could be implicated in the inhibitory action of the active compounds of the B. ruziziensis in E. heterophylla seedlings.
