Effect of caspase inhibitors and a cysteine protease inhibitor on TE formation in Zinnia cell cultures. A. Effect of inhibitor concentrations on the percent of formed TEs; H - hormone induced culture; B. Effect of inhibitors on cell viability. The cells were treated with 1 mg/L NAA and 1 mg/L BA and combinations of these hormones with the broad spectrum caspase inhibitor Z-Asp-CH2-DCB, the irreversible caspase-1- inhibitor Ac-YVAD-CMK, the reversible caspase 3 inhibitor Ac-DEVD-CHO and the cysteine protease inhibitor E-64 at indicated concentrations. Control cell cultures were left untreated. Cell viability was scored 120 h after addition of the chemicals as a percentage of living cells to the total number of cells and the number of TEs was calculated as a percentage of formed TEs to the initial number of living cells. 0.002% FDA was used to stain the living cells and 0.0005% CFW was used to stain the secondary cell walls of the differentiated cells. Cell counting of three non overlapping microscopic fields per each sample was performed with a fluorescence microscope (Axiovert, Carl Zeiss, Darmstadt, Germany) at 100× magnification. Presented data are averages of at least three independent experiments. Error bars indicate SEM (n-1).