Fig. 1.

Role of phytochromes in germination at different temperatures. (A) Effect of temperature on germination. Ler wt seeds that had after-ripened for 3 months were pre-incubated on agar in the dark for 4 d at the indicated temperature (4, 22, 32, or 34 °C). After 4 d, seeds were transferred to 22 °C with a 12 h photoperiod, and radicle protrusion was monitored daily. Error bars represent the SE of nine replicates of 15 seeds each. The speed of germination depended on temperature (germination×temperature interaction: Wald χ²=36.46, P=0.006, df=18). (B) Effect of phytochrome mutants on germination. Ler wt seeds and phytochrome mutant seeds (after-ripened for 3 months) were pre-incubated on agar in the dark for 4 d at the indicated temperature (4, 22, or 32 °C). After 4 d, seeds were transferred to 22 °C and a 12 h photoperiod, and radicle protrusion was monitored after 10 d. Error bars represent the SE of nine replicates of 15 seeds each. Differences among genotypes depended on temperature (genotype×temperature interaction: Wald χ²=76.41, P<0.001, df=8; see Supplementary Table S1 for comparisons between Ler wt and mutant genotypes at each temperature). (C) Effect of temperature on PHY gene expression. Relative expression level of PHY genes in Ler wt seeds at different time points: dry seeds, 96 h pre-incubation (Pre-inc), and 24 h after transfer to permissive germination conditions (22 °C, 12 h photoperiod). mRNA levels were normalized to the AT4G34270 (TIP41-like) transcript. Error bars indicate the SE of three biological replicates. See Supplementary Table S2 for analysis of differences in transcript levels between temperature treatments.