In touch: plant responses to mechanical stimuli

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Abstract
Summary: Perception and response to mechanical stimuli are likely essential at the cellular and organismal levels. Elaborate and impressive touch responses of plants capture the imagination as such behaviors are unexpected in otherwise often quiescent creatures. Touch responses can turn plants into aggressors against animals, trapping and devouring them, and enable flowers to be active in ensuring crosspollination and shoots to climb to sunlit heights. Morphogenesis is also influenced by mechanical perturbations, including both dynamic environmental stimuli, such as wind, and constant forces, such as gravity. Even individual cells must sense turgor and wall integrity, and subcellular organelles can translocate in response to mechanical perturbations. Signaling molecules and hormones, including intracellular calcium, reactive oxygen species, octadecanoids and ethylene, have been implicated in touch responses. Remarkably, touch‐induced gene expression is widespread; more than 2.5% of Arabidopsis genes are rapidly up‐regulated in touch‐stimulated plants. Many of these genes encode calcium‐binding, cell wall modifying, defense, transcription factor and kinase proteins. With these genes as tools, molecular genetic methods may enable elucidation of mechanisms of touch perception, signal transduction and response regulation. Contents Summary 373 I. Introduction 374 II. Fast and fascinating – thigmonasty and thigmotropism 374 III. Subcellular touch‐induced movements 382 IV. Thigmomorphogenesis 382 V. Discovery of the Arabidopsis TCH genes 384 VI. Microarray identification of touch‐inducible genes 384 VII. Regulation of TCH gene expression 385 Acknowledgements 386 References 386