TURGOR AND CELL EXPANSION - BEYOND THE LOCKHART EQUATION

The rheology of the expanding cell wall is often analysed in terms of the Lockhart equation, which equates the expansion rate of a cell to m(P - Y), where m is the extensibility of the cell wall, P is the turgor pressure, and Y is a minimum value of P below which the cell will not grow. Many studies have shown that Y (and sometimes m) are variables which change in response to changes in P at a time scale of about 10 min. The result is that, apart from the transient responses, the expansion rate is often maintained at an approximately steady value despite changes in P. This paper describes a molecular model of the growing cell wall that accounts for how m and Y may vary to maintain a constant growth rate despite changes in turgor.