Figure 1.

Pre-irradiation with red light enhances phototropic responsiveness of etiolated seedlings in a phyA-dependent manner. Three-day-old etiolated WT (A) and phyA (B), phyB (C) and phyA phyB (D) mutant seedlings were maintained in darkness (Control) or irradiated with 20 μmol m⁻² s⁻¹ of over-head red light for 15 min (Red) before being placed into 0.5 μmol m⁻² s⁻¹ of unilateral blue light for 3 h. Hypocotyl curvatures were measured every 10 min and each value is the mean ± S.E. of 18–20 seedlings. Asterisks indicate significant differences between red light treated and control seedlings (P < 0.001, Student's t-test).