WALL EXTENSIBILITY - ITS NATURE, MEASUREMENT AND RELATIONSHIP TO PLANT-CELL GROWTH

Expansive growth of plant cells is controlled principally by processes that loosen the wall and enable it to expand irreversibly. The centra l role of wall relaxation for cell expansion is reviewed. The most com mon methods for assessing the extension properties of plant cell walls ('wall extensibility') are described, categorized and assessed critic ally. What emerges are three fundamentally different approaches which test growing cells for their ability (a) to enlarge at different value s of turgor, (b) to induce wall relaxation, and (c) to deform elastica lly or plastically in response to an applied tensile force. Analogous methods with isolated walls are similarly reviewed. The results of the se different assays are related to the nature of plant cell growth and pertinent biophysical theory. I argue that the 'extensibilities' meas ured by these assays are fundamentally different from one another and that some are more pertinent to growth than others.