The Stages of Cell Elongation

We seem to have digressed somewhat from our discussion of elongation. However the connection becomes clear immediately when we mention the fact that in elongation the vacuoles or the single central space for cell sap are expanded quite considerably by water uptake. Water uptake implies an increase in the suction pressure of the cell. According to the suction pressure equation Sc=Sj-W, this increase can be attained by either a rise in the osmotic pressure of the cell sap SfOX a decrease in the wall pressure W. 

Sometimes, but certainly not always, a correlation can be found between intensity of cell elongation and concentration of osmotically effective substances in the vacuole. Thus, we are left with the alternative decrease of wall pressure. This lowering of wall pressure is achieved by an enhancement of the plastic flexibility of the cell wall. Crosslinks between the macromolecules of the components of the cell wall are broken, the wall is plastically extended and after elongation has occurrred new crosslinks are formed. In the cell walls of the elongation zones of the oat coleoptile different kinds of macromolecules are found (Table 8). They can all be linked to each other through functional groups in the different molecules, i.e. they can form crosslinks. 

The suction pressure of the cell is increased by the enhancement of plasticity of the cell wall. This leads to the inflow of water into the vacuole and to cell elongation. 

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