Cytoplasmic drops covered with the tonoplast were prepared from internodal cells of Nitellopsis grown in fresh water. Applying the patch-clamp technique and the microinjection technique to such drops, we characterized the ion channels in the tonoplast. Both in cell-free patches and in the cytoplasmic-drop-attached patches, the tonoplast K+ channel was identified. The permeability ratio between Na+ and K+ was calculated to be 0.2. This channel would provide a molecular basis for the Na+/K+ exchange at the tonoplast. In cell-free patches, the K+channel was not activated by Ca2+. However, in the case of attached patches, microinjection of Ca2+ into a drop activated the K+ channel with a lag of a few seconds, suggesting that some cytoplasmic factor(s) may mediate the activation of the K+ channel by Ca2+. The conductance of this channel was not changed by cytoplasmic Ca2+, but the probability of opening increased markedly. In addition to the K+ channel, a second type of channel was also identified in cell-free patches. This channel may be the Cl- channel.
|Number of pages||6|
|Journal||Plant and Cell Physiology|
|Publication status||Published - 1991 Mar|
All Science Journal Classification (ASJC) codes
- Plant Science
- Cell Biology