Figure 1.

Sketch depiction of the different modes of deformation possible in a flexible membrane under the action of a constriction force (F_c) (representative of the constriction deformations in cellular plasma membranes at the site of cell division), and of external stress fields applied either transversally, as a hydrostatic osmotic pressure (Δp), or longitudinally, as a lateral membrane tension (Σ). Positive osmotic pressure (Δp > 0), represents a cell at the inflated state of turgor, whereas negative osmotic pressure (Δp < 0) is identified with a flaccid cellular membrane in a hypertonic medium. Regarding lateral membrane tensions, positive surface tension (Σ > 0) represents biological situations of membrane tension underlateral extensional stresses induced by cortical tensions induced by either the eukaryote cytoskeleton, or the peptidoglycan layer in bacteria; negative surface tension (Σ < 0) represents situations of regulated creation of membrane area under in situ membrane biogenesis, or membrane uptake from membrane shuttles coming from the metabolic route of lipid synthesis (lipid trafficking).