Diversity of abundant mRNA sequences and patterns of protein synthesis in etiolated and greened pea seedlings

The diversity of abundant mRNA sequences in various parts of 4-d etiolated pea seedlings (Pisum sativum L. var. Rondo CB) was compared by a cell-free translation of the mRNAs in the presence of ³⁵S]methionine and by an analysis of the products by two-dimensional electrofocussing/ electrophoresis (2D separation). The various parts of the seedlings were also examined for the pattern of protein synthesis in vivo. Proteins were labeled by injection of ³⁵S]methionine into the cotyledons, followed by 2D separation of the products. Over 95% of the abundant mRNA sequences and newly synthesized abundant polypeptides were shared by all parts of etiolated seedlings, including the cotyledons. However, a few distinct differences were observed when comparing mRNAs of roots and shoots; the most prominent among these were a group of six abundant mRNA sequences found exclusively in shoots. Only about 30% of the polypeptides synthesized on isolated RNA could be traced in equivalent positions on the gels as the polypeptides synthesized in vivo. Analysis of total RNA from light-grown pea seedlings showed the appearance of some twenty-five translation products not found with total RNA from etiolated seedlings, while about nine other translation products disappeared. At least ten of the light-induced RNA sequences were also present after growth in low-intensity red light (>600 nm) and are therefore thought to be controlled by the phytochrome system. Comparison of 11-d light-grown pea plants with 4-d light-grown seedlings did not reveal additional translatable RNA sequences, indicating that the major morphogenetic changes that occur after 4 d are not accompanied by significant changes in the pattern of abundant RNA sequences.