Extracellular ATP, nitric oxide and superoxide act coordinately to regulate hypocotyl growth in etiolated Arabidopsis seedlings.

Etiolated Arabidopsis thaliana seedlings germinated in the presence of reducing buffers such as reduced gluthathione (GSH) and dithiothreitol (DTT) have altered morphology. GSH and DTT inhibited hypocotyl elongation in a dose-dependent manner. The GSH-mediated effect was prevented by the simultaneous addition of extracellular ATP (eATP). NADPH oxidase (NOX) activity and endogenous nitric oxide (NO) generation were required to mediate eATP action on the hypocotyl elongation. A correlation was observed between hypocotyl length, eATP concentration and NO production. The action of eATP and NO on superoxide (O(2)(-)) accumulation and peroxidase activity was investigated. The O(2)(-) distribution was regulated by eATP and NO during hypocotyl elongation. Our data suggest that a finely tuned balance of redox status and optimal levels of ATP and NO are essential to regulate the hypocotyl elongation in the dark.