TRANSIENT LIGHT-INDUCED-CHANGES IN ION-CHANNEL AND PROTON PUMP ACTIVITIES IN THE PLASMA-MEMBRANE OF TOBACCO MESOPHYLL PROTOPLASTS

Rapid, transient changes of the membrane potential upon light transiti ons are generally observed in microelectrode studies, In a patch-clamp study similar responses to light transitions were found in current cl amp, Corresponding with the changes of membrane potential, light-induc ed current changes in voltage clamp were observed, This paper evaluate s the involvement of outward rectifying conductances and plasma membra ne bound H+-ATPases (proton pump) to these light responses in mesophyl l protoplasts of Nicotiana tabacum L. The contribution of K+-channels to these responses, could be minimized by variation of the holding pot ential or addition of the K+-channel blocker verapamil, It was conclud ed that light transitions modulate both proton pump and K+-channel act ivity, Effects of light on membrane current were not observed in root cells and chlorophyll-deficient cells, suggesting that the response re quires photosynthetic activity, However, blockers of photosystems and II did not affect current changes.