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EnvReg213-page4 - Mimosa pudica turgor changes are caused...

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Plant Environmental Regulators - 4 Thigmotropism Thigmotropic responses are those to pressure or touch. A tendril will coil around any object it touches. Cells of the tendril opposite where the tendril touches elongate more rapidly than cells touching the support, which shrink a bit. You can observe tendrils coiling. It takes about an hour to make one turn. Thigmotropic twining Thigmonastic Movement Nastic movements are movements in which the direction of the movement is unrelated to the position of the original stimulus. Many plants have sudden responses to touch. All of these involve turgor changes in specialized cells. The trigger for the loss of turgor varies from electrical charges to rapid expansion of different tissue areas of the plant. In the sensitive plant,
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Unformatted text preview: Mimosa pudica , turgor changes are caused by water potential changes. • The water potential of the apoplast surrounding the pulvinus joint in the petiole of the leaf drops dramatically when sucrose is “dumped” by phloem in response to the pressure signal. (A pulvinus is a special "motor organ" comprised of parenchyma cells surrounding a vascular trace, usually found at the base of the petiole, capable of rapid turgor changes, hence collapsing the tissue.) • K + ions in the pulvinus cells move into the surrounding apoplast in response to the changed water potential. Water follows the solute gradient. • When the pulvinus cells lose turgor, the leaf collapses. This takes just a few seconds at most. Pulvinus structure...
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