Lysosomal Compartmentation: Ultrastructural Aspects of the Origin, Development, and Function of Vacuoles in Root Cells of Lepidium sativum

The origin and development of vacuoles in root and root capcells of Lepidium sativum was investigated at the ultrastructurallevel. The vacuoles originated as vesiculations of the ER, andacid phosphatase activity was found associated with the membranesbounding developing vacuoles. As development proceeded activityof acid phosphatase became associated with the accumulated vacuolarcontent, but was confined within these bodies in all cells exceptsome of those in the outermost layer of the cap, which werein various stages of senescence. In these cells activity ofthis enzyme appeared in the cytoplasm, associated with apparenttonoplast dissolution. These findings are discussed in the context of current hypothesesconcerning the origin and relationship of vacuoles and lysosomalcompartmentation in plant cells.