XVI International Botanical Congess

Plant cells store complex secondary metabolites, pigments, and proteins in vacuoles. Plant vacuoles also may have an acidic pH with active proteases. This apparent contradiction, storage proteins in vacuoles and active proteases in vacuoles, is resolved by the emerging understanding of how plant cells organize and maintain several different, functionally distinct vacuolar compartments. At present, three separate vacuole types can be recognized: protein storage vacuoles that contain seed-type storage proteins, delta vacuoles that contain vegetative storage proteins and pigments, and lytic vacuoles. In many cases, two separate types, and in some cases three types, coexist in the same cell. Lytic vacuoles appear to be converted to delta storage vacuoles by the addition of delta tonoplast intrinsic protein to their membrane. Pathways for delivery of membrane components to these vacuoles, and vesicular transport pathways to deliver soluble proteins to each type will be discussed.