Reduced maize leaf growth under salinity is associated with decreased reactive oxygen species concentration in the elongation zone

ANDRES RODRIGUEZ; HERNAN RAMIRO LASCANO; ALICIA CORDOBA; EDITH TALEISNIK

Lake Buena Vista, Florida USA.

Congreso; Plant Biology 2004; 2004

American Society of Plant Biologists

Reactive oxygen species (ROS) in the apoplast of cells in the growing zone of grass leaves are required for elongation growth. This work evaluates whether salinity-induced reductions in leaf elongation are related to altered ROS production. Studies were performed in actively growing segments (SEZ) obtained from leaf three of 14-days old maize seedlings gradually salinized to 150 mM NaCl. Salinity reduced elongation rates and the length of the leaf growth zone. When SEZ obtained from the elongation zone of salinized plants (SEZs) were incubated in 100 mM NaCl, concentration where growth inhibition was approximately 50%, O2- production, measured as NBT formazan staining, was lower in these than in similar segments obtained from control plants. The NaCl effect was salt-specific, and not osmotic, as incubation in 200 mM sorbitol did not reduce formazan staining intensity. SEZs elongation rates were higher in 200 mM sorbitol than in 100 mM NaCl, but the difference could be cancelled by scavenging or inhibiting O2-production (with 10 mM MgCl2 or 200 µM diphenyleneiodonium, respectively). SEZs elongation in 100 mM NaCl could be stimulated by a ·OH-generating medium. Fusicoccin, an ATPase stimulant, and acetate buffer pH 4, could also enhance elongation in these segments, though both failed to increase ROS activity. These results show that decreased ROS production contributes to the salinity-associated reduction in grass leaf elongation, acting through a mechanism not associated to pH changes.O2- production by plasma membrane fractions that required NADPH was also inhibited by the presence of NaCl and by Ca2+ scavengers, suggesting that plasmalemma NADPH oxidase activity may be responsible for apoplastic O2- presence, and that NaCl could negatively affect it.