Figure 7.

Determination of the [Ca²⁺] calibration curve for the plant ER‐targeted fl2‐AEQmut probe. Reconstituted protein crude extracts were obtained from Arabidopsis seedlings stably transformed with fl2‐AEQmut. Luminescence emitted at 22°C (L) upon injection of 200 µl of different Ca²⁺ concentrations to 50 µl of reconstituted extracts was measured. At the end of each experiment, the total residual luminescence (L _max) was collected by allowing full consumption of the probe via the addition of 50 μl of 1 m CaCl₂. The ratio L/L _max was plotted against actual [Ca²⁺]_free corresponding to the applied [CaCl₂], which was measured under the same conditions using the fluorescent calcium indicator Calcium Green™‐5N. Data are the mean ± SE of three different biological samples, each including three technical replicates. The continuous curve corresponds to the best fit of the experimental data, as described in the Experimental Procedures.