FIGURE 11.

Effect of cytokinin preincubation on freezing tolerance of ahk2, ahk3, and cre1 single mutants compared with the wild-type plants. A, ahk single mutants preincubated with or without cytokinin for 24 h. The ahk2-1, ahk3-1, cre1-12 mutants and the wild-type plants (Col-0) were grown for 9 days in the light, transferred to MS plate or MS plate containing 10 μm kinetin, and grown for an additional 24 h. These 10-day-old plants preincubated with or without cytokinin were subjected to freezing treatment at −5 °C for 6 h. The plants that survived after incubation at 23 °C for 2 days for recovery were counted. Experiments were conducted in triplicate, and the means ± S.E. were plotted. n ≥30. Statistically significant change with p < 0.01 (Student's t test) compared with the samples without cytokinin treatment is indicated by **. †† denotes statistically significant changes with p < 0.01 among ahk single mutants indicated. B, example plates showing the ahk2-1, ahk3-1, cre1-12 mutants, and the wild-type plants preincubated with or without cytokinin for 24 h, subjected to freezing treatment (A). C, ahk single mutants preincubated with or without cytokinin for 7 days. Plants were treated and analyzed as described in A except for 3 days growth followed by 7 days of incubation with cytokinin. D, example plates showing the ahk2-1, ahk3-1, cre1-12 mutants and the wild type plants preincubated with or without cytokinin for 7 days and then subjected to freezing treatment. Plant growth and cytokinin preincubation were conducted as described in C.