Plants cell wall loosening

Family of plant proteins essential for acid-induced cell wall loosening. See Cosgrove, D.J., Relaxation in a high-stress enviromnent the molecular basis of extensible cell walls and cell enlargement, Plant Cell 9, 1031-1041, 1997. 

The phenomenon is called cell wall loosening [2], in which the wall controls plant cell growth. The cell enlargement (elongation and/or expansion) substantially associates cellulose deposition during development. 

The structural xyloglucan molecules in the plant cell wall are subject to partial degradation in vivo [39-42]. This degradation, which may loosen the cell wall and thus favour cell expansion [6,43], was widely assumed to be due to hydrolysis, catalysed by cellulases. Recently, however, xyloglucan has been found to undergo a novel reaction in vivo — catalysed by XET [25,26,31,38,44-46]. The action of XET is proposed to occur in two steps -... 

D.J. Cosgrove. Cell wall loosening by expansins. Plant Physiol, 1998,118, 333-339 A.J. Fleming, S. McQueen-Mason, T. Mandel, C. Kuhlemeier. Induction of leaf primordia by the cell-wall protein expansin. Science, 1997, 276, 1415-1418... 

An open question is whether auxin stimulates wall loosening by acting at the level of gene transcription. Auxin certainly stimulates the rate of RNA synthesis in plant section,454-456 isolated nuclei,457-459 and chromatin,457,460 and new protein species appear after treatment of intact tissues with the hormone.461-463 However, the findings of Haschemeyer464 and Evans and Ray465 strongly indicated that the induction of cell-wall exten-... 

Loosening of the Cell Wall Permits Elongation of Plant Cells... 

The cell wall defines the shapes of plant cells and restricts their elongation. Auxin-Induced loosening of the cell wall permits elongation. 

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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