title: Effects of deuterium oxide on growth, proton extrusion, potassium influx, and in vitro plasma membrane activities in maize root segments.
abstract: Elongation of subapical segments of maize (Zea mays) roots was greatly inhibited by (2)H(2)O in the incubation medium. Short-term exposure (30 min) to (2)H(2)O slightly reduced O(2) uptake and significantly increased ATP levels. (2)H(2)O inhibited H(+) extrusion in the presence of both low (0.05 mm) and high (5 mm) external concentrations of K(+) (about 30 and 53%, respectively at 50% [v/v] (2)H(2)O). Experiments on plasma membrane vesicles showed that H(+)-pumping and ATPase activities were greatly inhibited by (2)H(2)O (about 35% at 50% [v/v] (2)H(2)O); NADH-ferricyanide reductase and 1,3-beta-glucan synthase activities were inhibited to a lesser extent (less than 15%). ATPase activities present in both the tonoplast-enriched and submitochondrial particle preparations were not affected by (2)H(2)O. Therefore, the effect of short incubation time and low concentration of (2)H(2)O is not due to a general action on overall cell metabolism but involves a specific inhibition of the plasma membrane H(+) -ATPase. K(+) uptake was inhibited by (2)H(2)O only when K(+) was present at a low (0.05 mm) external concentration where absorption is against its electrochemical potential. The transmembrane electric potential difference (E(m)) was slightly hyperpolarized by (2)H(2)O at low K(+), but was not affected at the higher K(+) concentrations. These results suggest a relationship between H(+) extrusion and K(+) uptake at low K(+) external concentration.
authors.affiliation: Dipartimento di Fisiologia delle Piante Coltivate e Chimica Agraria, Università di Milano, via Celoria 2, 20133 Milan, Italy.
authors.forename: G A
authors.initials: GA
authors.lastname: Sacchi
authors.forename: M
authors.initials: M
authors.lastname: Cocucci