Plant Sensing Touch and Leaf Movement
Plant cells have specialized structures called mechanoreceptors that detect touch and pressure. These mechanoreceptors are located in the cell walls of certain plant cells, especially in the stems and leaves. When these cells are mechanically stimulated by touch, they trigger a series of biochemical signals within the plant.

Signal Transduction Pathway
When a plant cell is touched, mechanoreceptors activate ion channels in the cell membrane, allowing ions like calcium to enter the cell. This influx of calcium ions initiates a cascade of signaling events that ultimately lead to changes in gene expression and protein production.

Leaf Movement Response
In response to touch, the plant may exhibit various types of leaf movements. For example, in the sensitive plant (Mimosa pudica), a touch to its leaves causes rapid leaf folding in a matter of seconds. This rapid movement is due to changes in turgor pressure within specialized cells called pulvini at the base of each leaflet.
In other plants, touch may induce slower responses such as leaf reorientation or curling. These movements are often controlled by changes in cell elongation and growth, which are regulated by the signal transduction pathways activated by touch.

Conclusion
In summary, plants detect touch through mechanoreceptors in their cells, which trigger a signal transduction pathway involving ion fluxes and gene expression changes. The specific response of the plant, such as leaf folding or reorientation, is determined by the type of plant and the mechanisms it has evolved to respond to touch stimuli.