Electrical perception of "death message" in Chara: involvement of turgor pressure.

Plants show various defense responses upon wounding. Surviving cells must perceive a "death message" from killed cells in order to start the signal processing that results in defense responses. The initial step in perception of the death message by a surviving cell was studied by taking advantage of the filamentous morphology of characean algae. A specimen comprising two adjoining internodal cells was prepared. One cell (the victim cell) was killed by cutting and any changes in the membrane potential of the neighboring cell (the receptor cell) were analyzed. Upon cutting the victim cell, at least one of three kinds of response were induced in the receptor cell: (1) slow depolarization lasting more than 10 min, (2) action potentials and (3) small spikes. The first of these response types, slow depolarization, was ubiquitous and is the focus of the present study. Two cell properties were essential for generation of this depolarization. (1) Presence of high cell turgor pressure was necessary. (2) The depolarization was generated only at the nodal end of the receptor cell, not at the flank. I concluded that the death message from the killed cell contains the information that turgor pressure has been lost. The mechanism by which this is translated into the slow depolarization of the receptor cell was discussed.