Figure 3. Ultrastructure of immature sunflower cotyledons and immunolocalization of storage proteins and vacuolar sorting receptors in the transport vesicles. Formation of electron-dense aggregates containing storage proteins began to be observed in the ER (part a, arrows). Further aggregation is observed in the trans-Golgi where dense vesicles (DV) bud off (part b). Immunogold labeling with serum specific to sunflower 11S globulin shows that electron-dense aggregates are composed by storage proteins (part c). Membranes in both DV and mutivesicular bodies are recognized by PV72-pumpkin- specific serum (part d).