Figure 6.

Effects of light fluence and spectral quality on SHM1 expression. A, Light fluence response of SHM1 mRNA accumulation. Total RNA was isolated from seedlings grown in constant darkness for 4 d and subjected to constant illumination for 24 h with white light at varying light intensities. Light intensities were, from left to right: 0, 2, 8, 15, 30, and 80 μE m⁻² s⁻¹. The panel was probed sequentially (see Fig. 1 legend) with SHM1 or rDNA as indicated. The induction relative to the SHM1 mRNA abundance in etiolated seedlings, arbitrarily defined as 1, was 24-, 32-, 85-, 109-, and 244-fold, respectively. B, Spectral quality response of SHM1 mRNA accumulation. RNA was isolated from seedlings grown in constant darkness (Dk) and subsequently transferred to 80 μE m⁻² s⁻¹ white light. Dk-->W, to 18 μE m⁻² s⁻¹ blue light; Dk-- >B, to 34 μE m⁻² s⁻¹ red light; Dk-->R, to 34 μE m⁻² s⁻¹ far-red light; Dk-->FR; Dk-->R+B, 34 μE m⁻² s⁻¹ red plus 18 μE m⁻² s⁻¹ blue light for 24 h. Additional etiolated seedlings were transferred to red light for 24 h followed by blue light for 24 h (Dk-->R-->B) or to blue light for 24 h followed by red light for 24 h (Dk-->B-->R). The panel was probed sequentially (see Fig. 1 legend) with SHM1 or rDNA.