Plants are unable to escape from harsh environments and perhaps as a consequence have evolved the ability to undergo adaptive changes in physiology and development. The mechanisms by which plants sense environmental stresses, transduce signals into cells and Braam Research regulate cellular and organismal alterations are largely unknown. We have taken a molecular approach to investigating these aspects of plant biology. The TCH genes of Arabidopsis are rapidly and strongly upregulated in expression in response to various environmental stimuli, including the seemingly innocuous stimulus of touch. These genes are powerful molecular tools for investigating how plants perceive environmental conditions and how they mount responses. We are investigating the cellular and genetic elements that control TCH expression and the biochemical and physiological functions of the TCH products. The TCH genes encode calmodulin, calmodulin-related proteins and a xyloglucan endotransglucosylase/hydrolase (XTH) predicted to act in modifying the plant cell wall. Current data support a hypothesis that the TCH proteins collaborate in the fundamental process of plant cell expansion.