Figure 1.

The ost2 mutations inhibit ABA-induced stomatal closure. (A) ost2-1D is stunted in development and prone to wilt relative to the wild-type Ler, even when well watered. (B) The kinetics of weight loss of detached leaves were compared between Ler and ost2-1D (mean value±s.d.; n=5). (C) ABA-induced stomatal closure. Epidermal peels with stomata pre-opened by light were incubated for 3 h with the indicated concentrations of ABA. ABA at 100 μM induces stomatal closure by 52% in Ler and 7% (^*) in ost2-1D. (D) Ca²⁺- and H₂O₂-induced stomatal closure. Epidermal peels with pre-opened stomata were incubated for 2 h with CaCl₂ or H₂O₂ at the indicated concentrations. (E) Stomatal opening in response to CO₂-free air was measured by using epidermal peels with pre-closed stomata incubated for 3 h in the dark with either normal or CO₂-depleted air. CO₂ (∼350 p.p.m.) inhibits stomatal opening by 72% in Ler and by 57% in ost2-1D. To measure stomatal closure stimulated by light to darkness transition, epidermal peels with stomata pre-opened by light were incubated for 2.5 h in darkness. Darkness induces stomatal closure by 61% in Ler and by 33% in ost2-1D. (F) ABA- and darkness-induced stomatal closure in the ost2-2D mutant and Col wild type. ABA at 100 μM induced stomatal closure by 66% in Col and by 5% (^*) in ost2-2D. Darkness induced stomatal closure by 58% in Col and by 24% in ost2-2D. Each experiment was repeated four times. Data from one representative experiment are shown as the mean value±s.e.m. (n=60 stomata). The asterisk (^*) indicates no statistical difference from 0 μM ABA (P⩽0.05).