Plasma membrane expansion

The resulting increased turgor in the periplasm is thought to buffer the cytoplasm against the loss of external osmolarity and to protect the periplasmic space from being eliminated by expansion of the plasma membrane. Related cyclic glucans, which are attached to sn-1 -phosphoglycerol or O-succinyl ester residues, are accumulated by rhizobia.s... 

The plasma membranes of growing plant cells select to incorporate sugars, amino adds, ions and other low molecular weight compounds from the apoplastic space, and then, the cells have a certain level of osmotic pressure. The difference between their osmotic pressure and their wall pressure (=turgor pressure) is due to motive power (suction force) to suck water from the apoplastic space (Figure 1). The plant hormone auxin, which decreases the wall pressure in a growing plant cell, therefore induces cell elongation or expansion. 

Fig. 7. Reversible trapping of synaptic vesicle membrane in the plasma membrane in reticulospinal synapses. (A) Electron micrograph of a lamprey reticulospinal synapse stimulated with action potentials at 20 Hz for 20 min and then incubated for 90 min in Ca " -free solution with 10 mM EGTA. Note the reduction in the number of synaptic vesicles and the presence of large membrane expansions compared to an unstimulated synapse (inset). (B) Activation of clathrin-mediated endocytosis in reticulospinal synapses by addition of Ca +-containing extracellular solution. Spinal cord preparations were stimulated at 20 Hz for 20 min, incubated for 90 min in Ca -free solution, and then incubated in Ca -containing solution (2.6 mM) for 120 s. Electron micrograph of a synapse shows the appearance of coated pits (arrows) lateral to the active zone. Designations as in Fig. 1. Scale bar, 0.2 p.m. Modified from Gad et al. (1998) Neuron 21 601-616, with permission copyright is held by Cell Press.

Auxin has been implicated in a bewildering array of growth responses. At the level of the cell, these responses involve rapid changes in cell expansion, effects on cell division and meristem activity, as well as differentiation of specific cell types [1]. In an effort to understand molecular aspects of auxin signaling, many researchers have focused on rapid biochemical responses associated with auxin-induced cell elongation. These include activation of a plasma membrane H -ATPase [2], changes in the behavior of ion channels... 

Pagant S., Bichet A., Sughnoto K., Lerouxel O., Desprez X, McCan M., Lerouge R, Vernhetles S., and Hofte H. (2002). KOBIXOl encodes a novel plasma membrane protein necessary for normal synthesis of cellulose during cell expansion in Arabidopsis. Plant Cell 14 2001-2013. 

Maeda, M., and G.A. Thompson, Jr., J. Cell Biol. 102 289-297 (1986). On the mechanism of rapid plasma membrane and chloroplast expansion in Dunaliella salina exposed to hypoosmotic shock. 

A plant cell may have to accommodate a 1,000-10,000-fold increase in volume and in length from its size at the time it is formed until the time it is fully expanded. The wall remains more or less the same thickness during expansion of the cell. Thus cell expansion requires the synthesis of new wall material. The expansion itself is driven by the cell turgor pressure, typieally 0.3-1 MPa, and results in wall stresses of 10-100 MPa [16]. The loosening of wall structure required to accommodate the expanding protoplast involves insertion of new wall material that must be strictly regulated to avoid stress-induced blebbing or rupture of the plasma membrane and... 

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