How Do the Cells on the Opposite Side of the Tendril Sense the Stimulus?
The question of how the touch stimulus is transduced from the site of contact to the sites of differential growth is quite complicated. First of all, it is believed that different species of plants transduce this signal in different ways. Secondly, numerous possible mechanisms exist by which this signal could be transduced. However, we know that the signal must orignate from the epidermal cells, because these are the cells which are in direct contact with the touch stimulus. The epidermal cells of most tendril tips have a very dense distribution of “hairs”, or tactile papillae, as well as plasmodesmata. When these hairs are touched, the membrane of the cell is temporarily deformed. This membrane deformation causes a change in the cell’s ionic permeability, which results in a regulatory action potential. This action potential causes turgor movements which drive the initial curving response. In addition, the high concentration of plasmodesmata on the epidermal cells of tendrils suggests
