Ultrastructural Studies Plasma Membrane Related Secondary Vacuoles in Cultured Cells

Abstract

The plasma membrane of cultured cells of several plant species was observed to possess invaginations, or secondary vacuoles, of variable size in the adjacent cytoplasm. These structures, which occurred in cells at different phases in vacuolation, were very numerous in thin sections of some cells but fewer in others. In vacuolated cells enlarged secondary vacuoles protrude into the primary vacuole but are delimited from the tonoplast by an intermembrane zone of variable width. The plasma membrane at the orifice of an invagination may fuse and detach the secondary vacuole from the membrane to form in the cytoplasm a structure bounded by a single membrane. Complex accumulations of membranes consisting of spherical, tubular, and laminar structures, possibly containing cytoplasm, may develop within secondary vacuoles. Contents of many of these vacuoles arise from folds along its limiting membrane which pinch off into the interior of the secondary vacuole. A fibrous substance, possibly derived from the wall, is present in some secondary vacuoles. Observed folding of the plasma membrane and measurements of membrane width of various organelles and cytomembranes support an interpretation that endocytosis occurs in cultured cells.

Leaf‐shape remodeling: programmed cell death in fistular leaves of Allium fistulosum

“…Complex accumulations of membranes consisting of vesicles, tubular structures or fibrous substances may develop within secondary vacuoles. Mahlberg et al () investigated the folding of the plasma membrane and measured the membrane width of various organelles and cytomembranes; the results supported an interpretation that the contents of these accumulations pinch off into the interior of the secondary vacuole by endocytosis (Walkinshaw et al , Mahlberg et al ). Secondary vacuoles were also detected in the development of A. fistulosum leaves.…”