A mild, 2-h cold shock treatment, from 24 to 16 °C, was applied during the different stages of Marsilea vestita embryogenesis. For each main stage (proembryo, globular embryo, and completed embryo with a bilateral symmetry), cold-induced modifications in RNA and protein synthesis were studied by autoradiography of the cells after incorporation of [5-3H]uridine and [3H]leucine. In both controls and treated specimens, proembryogenesis was characterized by a lack of transcriptional activity and no labelling was detected in the cytoplasm until the 16-cell stage. Even in the absence of de novo RNA synthesis in cooled samples, proteins necessary for the first cleavages of the embryo were being synthesized, but always at a rate lower than in the reference material. These results lead us to postulate that long-lived mRNA is stored in the cytoplasm of young embryos. Transcription, slowed down by the cold treatment, starts at the 8- to 16-cell stage and increases during the globular embryo stage. In lowered temperature conditions, transport of new RNA transcripts to the cytoplasm, which was strongly inhibited during the transition from the 16- to the 64-cell stage, appears to be less sensitive to cold shock as the embryo gets older. Our results show a difference in the response to temperature between RNA and protein synthesis. However, in both cases, sensitivity to cold temperature stress decreases with age. It is the physiological status reached by the embryo when the cold temperature stress is applied that determines the intensity of the response. [Journal translation]
Independence of 1,25-dihydroxyvitamin D3-mediated calcium transport from de novo RNA and protein synthesis.
