Extracellular ATP Signaling Is Mediated by H(2)O(2) and Cytosolic Ca(2+) in the Salt Response of Populus euphratica Cells

Extracellular ATP (eATP) has been implicated in mediating plant growth and antioxidant defense; however, it is largely unknown whether eATP might mediate salinity tolerance. We used confocal microscopy, a non-invasive vibrating ion-selective microelectrode, and quantitative real time PCR analysis to evaluate the physiological significance of eATP in the salt resistance of cell cultures derived from a salt-tolerant woody species, Populus euphratica. Application of NaCl (200 mM) shock induced a transient elevation in [eATP]. We investigated the effects of eATP by blocking P2 receptors with suramin and PPADS and applying an ATP trap system of hexokinase-glucose. We found that eATP regulated a wide range of cellular processes required for salt adaptation, including vacuolar Na(+) compartmentation, Na(+)/H(+) exchange across the plasma membrane (PM), K(+) homeostasis, reactive oxygen species regulation, and salt-responsive expression of genes related to K(+)/Na(+) homeostasis and PM repair. Furthermore, we found that the eATP signaling was mediated by H(2)O(2) and cytosolic Ca(2+) released in response to high salt in P. euphratica cells. We concluded that salt-induced eATP was sensed by purinoceptors in the PM, and this led to the induction of downstream signals, like H(2)O(2) and cytosolic Ca(2+), which are required for the up-regulation of genes linked to K(+)/Na(+) homeostasis and PM repair. Consequently, the viability of P. euphratica cells was maintained during a prolonged period of salt stress.