Developmental Regulation of the Synthesis of Proteins Encoded by Stored mRNA in Radish Embryos

Major radish (Raphanus sativus L. cv National) proteins synthesized at the beginning of germination have been characterized by their migration in two-dimensional electrophoresis.The use of 15-minute labelings shows that these proteins are encoded by stored mRNA. They undergo little or no posttranslational modification. Other proteins become detectable only after 1 hour of imbibition, and are probably encoded by newly synthesized mRNA. Comparison with proteins synthesized during embryogenesis, late germination, or with those present in dry embryos allows the classification of the proteins encoded by stored mRNA into two sets:The first set is synthesized also during late embryogenesis and is present in dry embryos. Some of these polypeptides are no longer synthesized later in germination while the others continue to be synthesized. The corresponding stored mRNAs can be considered as remnants of mRNA actively translated during embryogenesis.The second set is synthesized only during early germination. Their messengers appear during late embryogenesis although they are apparently not translated at this stage, but translation can be induced by a desiccation treatment. These polypeptides may play a particular role during early germination.