Vacuolar storage proteins are sorted in the cis-cisternae of the pea cotyledon Golgi apparatus

Developing pea cotyledons contain functionally different vacuoles, a protei n storage vacuole and a lytic vacuole. Lumenal as well as membrane proteins of the protein storage vacuole exit the Golgi apparatus in dense vesicles rather than in clathrin-coated vesicles (CCVs). Although the sorting recept or for vacuolar hydrolases BP-80 is present in CCVs, it is not detectable i n dense vesicles. To localize these different vacuolar sorting events in th e Golgi, we have compared the distribution of vacuolar storage proteins and of or-TIP, a membrane protein of the protein storage vacuole, with the dis tribution of the vacuolar sorting receptor BP-80 across the Golgi stack. An alysis of immunogold labeling from-cryosections and from high pressure froz ensamples has revealed a steep gradient in the distribution of the storage proteins within the Golgi stack. Intense labeling for storage proteins was registered for the cis-cisternae, contrasting with very low labeling for th ese antigens in the trans-cisternae. The distribution of BP-80 was the reve rse, showing a peak in the trans-Golgi network with very low labeling of th e cis-cisternae. These results indicate a spatial separation of different v acuolar sorting events in the Golgi apparatus of developing pea cotyledons.