Transitory development of rough endoplasmic reticulum aggregates during embryo maturation in seeds of mustard (Sinapis alba L.).

During the final period of maturation of mustard (Sinapis alba L.) seeds conspicuous aggregates of rough endoplasmic reticulum are found specifically in some tissues of the differentiation zone of the radicle. The appearance of these structures is temporally correlated with the disappearance of single-stranded reticulum and the onset of seed dehydration. These aggregates can be demonstrated also in the dry, mature seed and during the first few hours after imbibition with water; they disappear however during germination. In germinated root tips reformation of the aggregates can be induced by severe water stress. It is concluded that the observed membrane aggregates represent a storage form of rough endoplasmic reticulum during periods of low protoplasmic hydration.