QUINCLORAC-INDUCED ELECTROLYTE LEAKAGE IN SEEDLING GRASSES

The mode of action of quinclorac was investigated in broadleaf and gra ss species. Quinclorac induced characteristic auxin-like symptoms in b roadleaf species but not in susceptible grasses. In susceptible grasse s, quinclorac caused necrotic bands near the zones of elongation in sh oots and roots. Electrolyte leakage was induced by quinclorac in smoot h crabgrass and other susceptible grasses but not in tolerant grass or susceptible broadleaf species. In smooth crabgrass, increased electro lyte leakage and reduced fresh weight were rate dependent, and initial ly specific to young tissues. An inhibitory effect on elongation in th e youngest leaf of smooth crabgrass and in primary roots of corn was d etected 6 and 3 h after quinclorac treatment, respectively. Electrolyt e leakage required more than 12 and 6 h in the leaf and root, respecti vely. Depolarization of corn root cell membrane potential was not obse rved in a 6-h treatment period. Results presented here provide additio nal evidence that quinclorac activity differs between susceptible broa dleaf and grass species. In addition, the action of quinclorac appears to be similar in both shoot and root tissues of susceptible grasses. It is proposed that quinclorac-induced electrolyte leakage in suscepti ble grasses is a secondary response and that the primary mechanism of action involves inhibition of an as yet unknown metabolic process asso ciated with cell expansion.