Extracellular ATP released by copper stress could act as diffusible signal in alleviating the copper stress-induced cell death

In the present work, by using tobacco cell suspension and wheat seedlings, we studied that eATP (extracellular ATP) released by copper (Cu) stress could act as diffusible signal in alleviating the Cu stress-induced cell death. A semipermeable membrane was fixed in the middle of a plastic box to divide the box into two equal compartments (A and B, respectively). This semipermeable membrane can prevent direct cell-to-cell (or seedling-to-seedling) contact and the diffusion of the macromolecules [such as ATPase (adenosine 5-triphosphatase)] between these two compartments. The cell suspension directly stressed with CuCl2 was placed in compartment A and was incubated with the untreated cell suspension in compartment B. Such treatment significantly increased the levels of cell death and eATP content of the cell suspension in these two compartments. In contrast, addition of ATPase into the cell suspension directly stressed with CuCl2 decreased the eATP level in these two compartments but further increased the level of cell death in compartment B, compared to no addition of ATPase. Similar results were obtained when tobacco cell suspension was replaced by wheat seedlings. These observations indicate that when Cu stress from compartment A induced the plant cell death in compartment B, ATP transferred from compartment A could play a role in alleviating this cell death. Thus, it is suggested that eATP released by copper stress could act as diffusible signal in alleviating the Cu stress-induced cell death.