Physics of Root Growth

THE elongation of a plant cell involves the yielding of the cell wall under the action of tensile stresses in the wall¹. The rate of elongation, R, can be expressed simply as R=mW, where m is the extensibility of thé cell wall material and W is the wall pressure. Changes in either m or W have been used to explain the effect of biochemical factors on the growth rate of plant cells^2,3. Cell growth is also affected by the physical environment and this becomes particularly important in the case of plant roots where soil water potential and the mechanical resistance of the soil to deformation can become rate controlling. Working with 3-5 day old radicles of Pisum sativum, growing in soil cores, we have obtained values of wall pressure in terms of these two properties and we find that the rate of root elongation can be described by a simple extensibility equation.