A comparison of the activation of ribosomal RNA synthesis during germination of isolated and non-isolated embryos of Triticum aestivum L

Increase of protein synthesis after isolation in dormant and afterripened Agrostemma githago L. embryos

Isolated embryos are more suitable for in vivo study of protein synthesis than non-isolated embryos because, after isolation, the uptake of labeled amino acids is about 1000 times higher. However, isolation also stimulates protein synthesis: Up to 4 h after isolation, the capacity to incorporate labeled amino acids increased 7 times. Therefore, data on incorporation obtained with isolated embryos cannot be extended to non-isolated embryos. The increase of protein synthesis was not due to synthesis of specific proteins, but was a general increase. Furthermore, ripening, dormant, and afterripened embryos showed the same degree of increase. Isolation therefore stimulates protein synthesis nonspecifically. When embryos were kept under anaerobic conditions after isolation, protein synthesis did not increase. Therefore, higher oxygen consumption after removal of the seedcoat is probably the cause of the higher incorporation capacity. Furthermore, the activation of protein synthesis lagged several hours behind the increase of oxygen consumption.

Ribosomal RNA synthesis in imbibing radish (Raphanus sativus) embryo axes : A biochemical and cytological study

The first hours of seed germination are characterized by an increase in the rate of RNA synthesis. Although this change is most easily accounted for by changes in the ribonucleotide pool sizes, we investigated two other aspects of rRNA synthesis which are likely to contribute to the phenomenon. Using isolated radish embryo axes, we demonstrate that processing of rRNA gene transcripts is much slower during early germination than during the growth of the seedling. We also provide evidence that rRNA gene expression is sequentially reactivated in different tissues, starting in the provascular tissue and apex cells and only later in the cortical cells of the rootlet.

Membrene turnover in imbibed and dormant embryos of the wild oat (Avena fatua L.) : I. Protein turnover and membrane replacement

A comparative study of protein synthesis has been carried out with embryos excised from dormant (D) and non-dormant (ND) caryopses of the wild oat. Although D embryos imbibed in water or ND embryos imbibed in abscisic acid do not germinate, they incorporate [(14)C]leucine into TCA-insoluble material for the first 48 h as readily as embryos that do germinate (ND embryos imbibed in water, or D embryos imbibed in gibberellic acid). Pulsechase experiments with [(14)]leucine show that in both D and ND embryos the proteins associated with the membranes undergo turnover. The rates of decay of incorporated radioactivity are similar in both dormant and germinating embryos up to 98 h following embryo excision. Fractionation of the membrane proteins in SDS-polyacrylamide gels indicates that the different polypeptides have different rates of turnover. It is concluded that membrane proteins in imbibed D embryos are in a state of constant turnover, and that this is a part of the replacement processes necessary to maintain the integrity of hydrated cells. The continuation of such synthetic events could account for long term survival of dormant Avena fatua in the imbibed state.