Figure 4.

Characterization of callose synthase activity. (A) Experiments were performed on Col-0 cells treated with 20 μg ml^-1 of alamethicin in assay medium complemented with various amounts of Ca²⁺, Mg²⁺ and isoxaben (Isox.). Activities for each independent experiment are presented relative to the activity in the presence of 1 mM Ca²⁺. The average activity with 1 mM Ca²⁺ was 45 nmol min^-1 g^-1(FW). Values represent averages of at least three independent experiments except for the 2 mM Mg²⁺ experiment which was determined twice. (B) The effect of ethanol addition of callose synthase activity in Col-0 and BY-2 cells. Each curve represents one independent experiment. The maximum activity was 45 nmol min^-1 g^-1(FW) in Col-0 and 10 nmol min^-1 g^-1(FW) in BY-2 cells.