Fig. 3: FT1 and GA mediate the variable cold response of buds.

a Relative expression of FT1 in wild-type buds after 11 weeks of short-day (SD), followed by 4 weeks of constant cold and variable cold temperatures. Expression values shown are normalized to the reference gene UBQ and are averages of three biological replicates. Each biological replicate consists of three buds. Error bars indicate standard error mean ( ± SEM). Statistical significance was determined using one-way ANOVA and multiple comparison by the Holm–Sidak method (P < 0.05). Letters above the bars indicate significant differences. b, d High-resolution TEM images of PD ultrastructure and anti-callose labeling (10 nm gold particles) in aspen buds. b WT and FT1crispr (ft1) after 11 weeks of SD and 4 weeks of cold. d WT and FT1 inducible line (XVE::FT1-GFP-HA) under mock and estradiol treatment. Scale bars = 0.1 µm. Plants were shifted to SD conditions for 11 weeks to induce bud formation. Estradiol treatment was done in the SD condition and samples were collected after 2 weeks for TEM analysis. c, e Callose quantification based on the number of gold particles in PDs. Different letters indicate significant differences based on a one-way ANOVA (p < 0.0001) followed by Tukey’s test. f Bud break analysis in WT and XVE::FT1-GFP-HA line treated with mock or estradiol. g Response of WT, ft1, abi1-1 and abi1-1/ft1 buds exposed to constant vs. variable cold temperatures. Plants were grown under short-day (SD) conditions for 11 weeks, followed by either 4 weeks of constant cold or variable cold temperatures (as described in Fig. 1a) then transferred to warm, long-days, and bud break was recorded. h Relative expression of GA20ox in wild-type buds after 11 weeks of SD, followed by 4 weeks of constant cold and variable cold temperatures. Expression values shown are normalized to the reference gene UBQ and are averages of three biological replicates, each consisting of three buds. Error bars indicate standard error mean ( ± SEM). Statistical significance was determined as indicated in Fig. 3a. i Response of WT and GA20oxOE buds exposed to constant vs. variable cold temperatures. Plants were grown constant and variable cold conditions as described in Fig. 3g.