Light‐ and phytochrome‐mediated gene expression in Douglas‐fir seedlings

Abstract

In dark‐grown Douglas‐fir [Pseudotsuga menziesii (Mirb.) Franco] seedlings, the steady‐state level of the major light‐harvesting chlorophyll a/b binding proteins mRNA (cab mRNA) was about 25% of the level that accumulated in light‐grown seedlings. A single, 5‐min irradiance with red light up‐regulated expression transiently, so that cab mRNAs accumulated to a Jevel approaching that determined for light‐grown seedlings. The response was reversible by far‐red light to the dark level, indicating that the up‐regulation was a phytochrome‐mediated response. Phytochrome action also up‐regulated genes that encode ribulose bisphosphate carboxylase/oxygenase (EC 4.1.1.39) (rbcS) in Douglas‐fir seedlings, but the maximal rbcS mRNA level that was attained after the red light treatment was several‐fold lower than the expression level deternined for light‐grown seedlings. Genes that produce ubiquitin and ubiquitin‐fusion transcripts were differentially expressed in dark‐ and light‐grown seedlings, but the genes did not appear to be phytochrome regulated.