Disruption of inward K⁺ channel activity affects stomatal circadian rhythm and renders stomatal opening sensitive to the duration of the preceding photoperiods. (A and B) Effect on stomatal circadian rhythm. (A) Continuous recording of the transpiration rate in a single WT or kincless plant during 7 days. Black and white boxes under the curves indicate dark and light periods, respectively. Two photoperiods were suppressed, on days 4 and 5. (B) Enlargement from A (dotted boxed regions) highlighting stomatal preopening in darkness in the WT plant. (C and D) Sensitivity to the duration of the preceding photoperiods. (C) Transpiration rates recorded in 5-week-old WT or kincless plants exposed to an 8-h photoperiod since sowing. (D) Transpiration rates recorded in the same plants after exposure to a 3-h photoperiod during 2 days. Data are means ± SE; n = 15 plants per genotype.