Wall extensibility: its nature, measurement and relationship to plant cell growth

SUMMARY Expansive growth of plant cells is controlled principally by processes that loosen the wall and enable it to expand irreversibly. The central role of wall relaxation for cell expansion is reviewed. The most common methods for assessing the extension properties of plant cell walls (‘wall extensibility’) are described, categorized and assessed critically. What emerges are three fundamentally different approaches which test growing cells for their ability ( a ) to enlarge at different values of turgor, ( b ) to induce wall relaxation, and ( c ) to deform elastically or plastically in response to an applied tensile force. Analogous methods with isolated walls are similarly reviewed. The results of these different assays are related to the nature of plant cell growth and pertinent biophysical theory. I argue that the ‘extensibilities’ measured by these assays are fundamentally different from one another and that some are more pertinent to growth than others. ‘That's a great deal to make one word mean,’ Alice said in a thoughtful tone. ‘When I make a word do a lot of work like that’ said Humpty Dumpty,‘I always pay it extra’. ‘Oh!’ said Alice. She was too much puzzled to make any other remark. Lewis Carroll, Through the Looking‐glass CONTENTS Summary 1 I. Introduction 1 II. The nature of wall expansive growth 2 III. Techniques for measuring wall extensibility 4 IV. Concluding remarks and prospectus 20 Acknowledgements 20 References 20