Sequence complexity of messenger RNA in cotyledons of developing pea ( Pisum sativum) seeds

Abstract

The hybridization kinetics of poly(A) +-RNA preparations from the cotyledons of developing pea ( Pisum sativum seeds to complementary DNAs have shown that the number of distinct sequences in poly(A) + -RNA decreases from ca 20 000 at the early stage of cotyledon development to ca 200 at a late stage of cotyledon development. The decrease in sequences is accounted for entirely by the disappearance of ‘rare’ poly(A) + -RNAs (< 10 3 copies/cell) as seed development proceeds. There is an increase (1–6) in very abundant poly(A) +-RNA sequences (⪢ 5 × 10 5 copies/cell) from early- to mid-developmental stages, concomitantly with the increase in the synthesis of seed-specific storage protein polypeptides. In agreement with the continuing synthesis of most of these polypeptides to the end of seed development, the number of very abundant poly(A) +-RNAs is maintained to the late cotyledon development stage. Abundant poly(A) +-RNA sequences ( ca 10 4 sequences/cell) increase from 80 to 180 during development, possibly corresponding to the polypeptides which are not storage proteins but are known to be accumulated in pea seeds. Hybridization of single-copy pea genomic DNA sequences to poly(A) +-RNA from developing seeds showed that ca 5 % of the single-copy sequences were present in mRNA from mid-development cotyledons. In addition, hybridization of cDNA prepared against poly(A) +-RNA from nuclei of early development cotyledons to the corresponding cytoplasmic polysomal poly(A) +-RNA showed that the cytoplasmic poly(A) +-RNA contained ca 50 % of the sequences present in the nuclei. These results are discussed and interpreted in the light of existing results from similar systems.