The signaling role of extracellular ATP and its dependence on Ca2+ flux in elicitation of Salvia miltiorrhiza hairy root cultures

The application of a polysaccharide elicitor from yeast extract,YE, to Salvia miltiorrhiza hairy root cultures induced transientrelease of ATP from the roots to the medium, leading to a dose-dependentincrease in the extracellular ATP (eATP) level. The eATP levelrose to a peak (about 6.5 nM with 100 mg l^–1 YE) at about10 h after YE treatment, but dropped to the control level 6h later. The elicitor-induced ATP release was dependent on membraneCa²⁺ influx, and abolished by the Ca²⁺ chelator EGTA or thechannel blocker La³⁺. The YE-induced H₂O₂ production was stronglyinhibited by reactive blue (RB), a specific inhibitor of membranepurinoceptors. On the other hand, the application of exogenousATP at 10–100 µM to the cultures also induced rapidand dose-dependent increases in H₂O₂ production and medium pH,both of which were effectively blocked by RB and EGTA. The non-hydrolyzableATP analog ATPS was as effective as ATP, but the hydrolyzedderivatives ADP or AMP were not so effective in inducing thepH and H₂O₂ increases. Our results suggest that ATP releaseis an early event and that eATP plays a signaling role in theelicitation of plant cell responses; Ca²⁺ is required for activationof the elicitor-induced ATP release and the eATP signal transduction.This is the first report on ATP release induced by a fungalelicitor and its involvement in the elicitor-induced responsesin plant cells.