Ca2+-dependent excretion of salicylic acid in tobacco cell suspension culture

The radioactive C-14-Salicylic acid (SA) was used to monitor the metabolism of exogenous SA in tobacco cell suspension culture. Tobacco cells took up ca. 39.46% of the applied SA 5 min after the addition of a final 200 mu M SA mixture containing [C-14]SA to the cell suspension culture. Most of the SA absorbed by the cells was gradually lost to the culture medium, and 2.62% and 91.55% of the radioactivity were found in the cells and the culture filtrate, respectively, 5 h after treatment. Excretion of SA to the culture medium required external Ca2+ and was inhibited by EGTA pretreatment. The inhibition was reversible through the supplement of Ca2+ to the cell suspension culture. Based on the data, we conclude that SA excretion from the 200 mu M-treated cells requires external Ca2+ and likely involves a putative Ca2+-dependent pathway in tobacco suspension culture.