Figure 2.

Cold priming response of constantly and repetitively cold-treated Arabidopsis seedlings with intermittent recovery phases of various length. (a,d,g) Schematic illustration of the treatments. 21-d-old seedlings treated constantly (a,b,c), every night (d,e,f) or every second night (g,h,i) with 4 °C. (b,e,h) Analysis of freezing resistance by electrolyte leakage measurements (LT₅₀). (c,f,i) Induction of the cold response gene COR15A measured by qRT-PCR. Expression in non-primed control seedlings at the given sampling time (morning or evening) was set to 1. For (d,g) the cold stress response was tested after the given treatments (P1-P7) and after a 8-h or 32-h recovery phase at 22 °C (lag phase; L8h, L32h). For comparison, similar time points were chosen to monitor the response to a constitutive cold stress treatment of seven days (a). Non-cold treated plants (C; dotted line). Significance of differences between the conditions was calculated by one-way ANOVA. Identical letters indicate no significant difference (p < 0.05). Error bars represent standard deviation, n = 4. DAS, days after sowing.