One Vacuole or two Vacuoles: Do Protein Storage Vacuoles Arise de novo during Pea Cotyledon Development?

Using improved fixation procedures for both conventional and immuno-electron microscopy, we have reinvestigated the problem of protein storage vacuole (PSV) biogenesis in developing pea (Pisum sativum L.) cotyledons. Our results show that PSV develop de novo and the vegetative vacuoles degenerate. The PSV appear to arise from the rough ER as judged by the presence of osmiophilic substances in the lumen of rER cisternae and by the detection of a BiP analogue in the storage protein deposits contained in the young PSV. These results are discussed in terms of the involvement of other endomembrane compartments (Golgi apparatus and clathrin coated vesicles) in the intracellular transport of storage proteins in legumes.