Protein and nucleic acid synthesis during imbibition of dormant and after-ripened Vaccaria pyramidata seeds

Abstract

The regulation of nucleic acid and protein synthesis in dormant, thermodormant, and after-ripened embryos of Vaccaria pyramidata (Caryophyllaceae) has been studied. Germination of after-ripened V. pyramidata seeds is prevented by inhibitors of protein, RNA, and DNA synthesis. The synthesis of both protein and RNA is activated at the beginning of imbibition, whereas [ 3H]thymidine incorporation does not start until the second period of the imbibition phase. [ 3H]Thymidine incorporation is greatly reduced in embryos treated with cycloheximide or 6-methylpurine. There is no correlation between the level of [ 3H]uracil and l-[ 14C]leucine incorporation into macromolecules and the physiological state of the seeds: tRNA, ribosomal RNA, and poly(A)-containing RNA (probably mRNA) as well as proteins are synthesized at the same rate in both dormant and thermodormant embryos as in after-ripened embryos. The protein patterns of dormant and after-ripened embryos are similar, as shown by electrophoresis and electrofocusing of double-labeled proteins. The level of DNA synthesis, measured as [ 3H]thymidine incorporation, may, on the other hand, indicate the physiological activity of the seeds: [ 3H]Thymidine is incorporated at a high rate in after-ripened embryos only and remains at a low level in dormant or thermodormant embryos. This correlation is, however, observed only in the axes. DNA synthesis in the cotyledons does not show any relation to the developmental stage of the seeds. These results are discussed in relation to the regulation of dormancy and after-ripening of seeds.