The plant activator acibenzolar-S-methyl (BTH) undergoes phototransformation when exposed to solar radiation. Here we investigated the changes in its elicitation properties on BY-2 tobacco cells at different stages of the photochemical reaction. Both pure BTH and formulated BTH were irradiated in controlled conditions to achieve different extents of conversion. Both pure BTH (900 mu,M) and Bion (R) (0.4 g.L-1) induced BY-2 cell death, but BTH photoconverted to an extent of 25 +/- 3% lowered the cell death rate. A kinetic study of beta-1,3-glucanase and chitinase activities was conducted on BY-2 extracellular medium. Exposure of tobacco cells to either pure BTH or Bion (R) resulted in a significant increase in the activities of both defense enzymes, which peaked 48 h after the treatment. The pathogenesis-related (PR) protein activities were quantified 48 h after elicitation for a range of phototransformed BTH solutions. The enzyme activities were reduced when BY-2 cells were treated with solutions in which BTH conversion was 22 +/- 3%, 42 +/- 3% and 100 +/- 3%, but were not affected by the solution in which BTH was photo transformed at 60%, suggesting that some of the secondary photoproducts also exhibit eliciting properties. Solar irradiation of BTH thus impairs its elicitation properties, but this impairment depends strongly on the extent of phototransformation. (C) 2017 Elsevier Masson SAS. All rights reserved.