Figure 8.

DCMU Promotes a Light-Dependent Increase of Ca²⁺ in the Stroma but Does Not Inhibit the Dark-Stimulated Ca²⁺ Flux in LD 16:8.

DCMU or MS medium was added to MAQ 6.3 seedlings at h 44 of LD 16:8. A total of 200 μL of MS medium or of 100 μM DCMU (dissolved in MS medium) was added on top of seedlings on 2 mL of agar medium. The final DCMU concentration after diffusion into the agar medium was 10 μM. (C) and (D) show magnified versions of (A) and (B) ([C] is magnified from [A] and [D] is magnified from [B]). Representative traces are shown for measurements from 18 different samples for each treatment (two separate experiments with three DCMU treatments at 2 μM, three DCMU treatments at 10 μM, and three medium treatments in each experiment). To ensure that the signal observed with DCMU was specific for stroma-targeted aequorin (and not for, e.g., delayed fluorescence [Jursinic, 1986]), we also treated nontransgenic seedlings that had been incubated with coelenterazine and treated with DCMU. In those seedlings, there was no increase in basal luminescence levels after DCMU treatment, nor was there a dark-stimulated luminescence burst.