Multivesicular bodies in developing tobacco seed and mung bean are functionally equivalent

Protein storage vacuoles (PSVs) are the primarily storage organelles in cotyledon cells for protein preservation in seeds. Storage proteins are transported from the endoplasmic reticulum (ER) to the Golgi apparatus for subsequent delivery to PSVs via presumably Golgi-derived dense vesicles (DVs). However, recent studies demonstrated that storage proteins in early stage of developing cotyledon of mung beans reached the multivesicular bodies (MVBs) prior to the detection of DVs, indicating the possible involvement of MVBs in mediating transport of storage proteins during the early stage of seed development. Here, we further show that the MVBs in developing tobacco seeds are functionally and biochemically equivalent to those in developing mung beans. Thus, MVBs in developing tobacco seeds are structurally distinct from DVs, contain both vacuolar sorting receptors (VSRs) and storage proteins, and they are insensitive to treatments of wortmannin and brefeldin A (BFA).