Ionic homeostasis disturbance is involved in tomato cell death induced by NaCl and salicylic acid

The ability of salicylic acid and NaCl to induce programmed cell death by disturbing ionic homeostasis was investigated using tomato suspension culture cells. NaCl (300 mM) and salicylic acid (1 mM) inhibited cell growth and caused cell death within 1 wk of exposure. Treatment with NaCl increased the production of reactive oxygen species and the permeability of plasma membrane, but it also led to a reduction in the pH of the culture medium and resulted in a disturbance in ionic homeostasis of the cells. Salicylic acid-induced cell death in tomato suspension culture was also accompanied by production of reactive oxygen species and increases in both electrolyte leakage and pH of the culture media. However, reactive oxygen species production was not significantly different in cultures treated with a lethal salicylic acid concentration and 100 mM NaCl, in which most of the cells survived. A decrease in the K+/Na+ ratio was observed only in those cell cultures in which the salicylic acid treatment induced the death of cells. These results suggest that the decrease of the intracellular K+ concentration and K+/Na+ ratio is a common phenomenon in triggering programmed cell death by lethal concentrations of salicylic acid and NaCl.