Antibodies to the CFTR modulate the turgor pressure of guard cell protoplasts via slow anion channels

The plasma membrane guard cell slow anion channel is a key element at the b asis of water loss control in plants allowing prolonged osmolite efflux nec essary for stomatal closure. This channel has been extensively studied by e lectrophysiological approaches but its molecular identification is still la cking. Recently, we described that this channel was sharing some similariti es with the mammalian ATP-binding cassette protein, cystic fibrosis transme mbrane conductance regulator (CFTR) chloride channel [Leonhardt, N. et at. (1999) Plant Cell 11, 1141-1151]. Here, using the patch-clamp technique and a bioassay, consisting in the observation of the change in guard cell prot oplasts volume, we demonstrated that a functional antibody raised against t he mammalian CFTR prevented ABA-induced guard cell protoplasts shrinking an d partially inhibited the slow anion current. Moreover, this antibody immun oprecipitated a polypeptide from guard cell protein extracts and immunolabe led stomata in Vicia faba leaf sections. These results indicate that the gu ard cell slow anion channel is, or is closely controlled by a polypeptide, exhibiting one epitope shared with the mammalian CFTR, (C) 2001 Federation of European Biochemical Societies. Published by Elsevier Science B.V. All r ights reserved.