Plasma membrane NADH oxidase of maize roots responds to gravity and imposed centrifugal forces

NADH oxidase activities measured with excised roots of dark-grown maize (Ze a mays) seedlings and with isolated plasma membrane vesicles from roots of dark-grown maize oscillated with a regular period length of 24 min and were inhibited by the synthetic auxin 2,4-dichorophenoxyacetic acid. The activi ties also responded to orientation with respect to gravity and to imposed c entrifugal forces. Turning the roots upside down resulted in stimulation of the activity with a lag of about 10 min. Returning the sections to the nor mal upright position resulted in a return to initial rates. The activity wa s stimulated reversibly to a maximum of about 2-fold with isolated plasma m embrane vesicles, when subjected to centrifugal forces of 25 to 250 x g for 1 to 4 min duration. These findings are the first report of a gravity-resp onsive enzymatic activity of plant roots inhibited by auxin and potentially related to the gravity-induced growth response. (C) 2001 Editions scientif iques et medicales Elsevier SAS.