Gene Activity during Germination of Spores of the Fern, Onoclea sensibilis: RNA and Protein Synthesis and the Role of Stored mRNA

Pattern of ³H-uridine incorporation into RNA of spores of Onocleasensibilis imbibed in complete darkness (non-germinating conditions)and induced to germinate in red light was followed by oligo-dTcellulose chromatography, gel electrophoresis coupled with fluorographyand autoradiography. In dark-imbibed spores, RNA synthesis wasinitiated about 24 h after sowing, with most of the label accumulatingin the high mol. wt. poly(A)^–RNA fraction. There was noincorporation of the label into poly(A) ⁺ RNA until 48 h aftersowing. In contrast, photo-induced spores began to synthesizeall fractions of RNA within 12 h after sowing and by 24 h, incorporationof ³H-uridine into RNA of irradiated spores was nearly 70-foldhigher than that into dark-imbibed spores. Protein synthesis,as monitored by ³H-arginine incorporation into the acid-insolublefraction and by autoradiography, was initiated in spores within1–2 h after sowing under both conditions. Autoradiographicexperiments also showed that the onset of protein synthesisin the cytoplasm of the germinating spore is independent ofthe transport of newly synthesized nuclear RNA. One-dimensionalsodium dodecyl sulphate-polyacrylamide gel electrophoresis of³⁵S-methionine-labelled proteins revealed a good correspondencebetween proteins synthesized in a cell-free translation systemdirected by poly(A) ⁺RNA of dormant spores and those synthesizedin vivo by dark-imbibed and photo-induced spores. These resultsindicate that stored mRNAs of O. sensibilis spores are functionallycompetent and provide templates for the synthesis of proteinsduring dark-imbibition and germination. Key words: Onoclea sensibilis, fern spore germination, gene expression, protein synthesis, sensitive fern, stored mRNA