Modulation of Gene Activity During Photomorphogenesis of Gametophytes of the Fern, Onoclea sensibilis

Gametophytes of the sensitive fern, Onoclea sensibilis grow as filaments in the dark and in red light and assume planar morphology in blue light. RNA content and the synthesis of different RNA fractions as monitored by [ 3 H]‐uridine incorporation and chromatography on oligo(dT)‐cellulose column, were consistently low in the dark‐grown gametophytes, high in blue light and intermediate in red light. No new mRNAs were detected in the translation products primed by poly(A)+ RNA isolated from gametophytes grown under any conditions. Of the nearly 30 polypeptide bands identified in the in vitro profile, some increased in intensity in blue light, while most continued to decay in the dark and in red light. An increase in the intensity of the polypeptide bands was detected when dark‐ or red light‐grown gametophytes were returned to blue light. Abundance of mRNA of the gene for the large subunit of maize ribulose‐1,5‐bis‐phosphate carboxylase/oxygenase ( rbc L) remained more or less unchanged during growth of gametophytes in blue light but declined to very low or undetectable levels in red light and in the dark. Transfer of gametophytes from the dark or red light to blue light led to the reappearance of rbc L mRNA. Within the limits of detectability, these observations indicate that light quality or dark condition does not affect the expression of the genome, but modifies its relative transcriptional activity. Overall, the results support the hypothesis that changes in the rate of synthesis or degradation of certain mRNAs are associated with the growth patterns of gametophytes of O. sensibilis in the different environments.