Reversible inactivation of K+ channels of Vicia stomatal guard cells following the photolysis of caged inositol 1,4,5-trisphosphate.
RECENT investigations suggest that cytoplasmic D-myo-inositol 1,4,5-trisphosphate (InsP3) functions as a second messenger in plants, as in animals, coupling environmental and other stimuli to intracellular Ca2+ release. Cytoplasmic levels of InsP3 and the turnover of several probable precursors in plants are affected by physiological stimuli--including light, osmotic stress and the phytohormone indoleacetic acid--and InsP3 activates Ca2+ channels and Ca2+ flux across plant vacuolar and microsomal membranes. Complementary data also link changes in cytoplasmic free Ca2+ to several physiological responses, notably in guard cells which regulate gas exchange through the stomatal pores of higher plant leaves. Recent evidence indicates that guard cell K+ channels and, hence, K+ flux for stomatal movements may be controlled by cytoplasmic Ca2+. So far, however, direct evidence of a role for InsP3 in signalling in plants has remained elusive. Here we report that InsP3 released from an inactive, photolabile precursor, the P5-1-(2-nitrophenyl)ethyl ester of InsP3 (caged InsP3) reversibly inactivates K+ channels thought to mediate K+ uptake by guard cells from Vicia faba L. while simultaneously activating an apparently time-independent, inward current to depolarize the membrane potential and promote K+ efflux through a second class of K+ channels. The data are consistent with a transient rise in cytoplasmic free Ca2+ and demonstrate that intact guard cells are competent to use InsP3 in signal cascades controlling ion flux through K+ channels.
Blatt
M R
MR
Botany School, University of Cambridge, UK.
Thiel
G
G
Trentham
D R
DR
D002118:Calcium / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism; D004594:Electrophysiology / Q000379:methods; D015544:Inositol 1,4,5-Trisphosphate / Q000031:analogs & derivatives* / Q000378:metabolism; D007700:Kinetics; D008839:Microelectrodes; D010782:Photolysis; D018521:Plant Physiological Phenomena; D011188:Potassium / Q000378:metabolism; D015221:Potassium Channels / Q000502:physiology*; D015290:Second Messenger Systems
D015221:Potassium Channels; C061868:inositol 1,4,5-trisphosphate 1-(2-nitrophenyl)ethyl ester; D015544:Inositol 1,4,5-Trisphosphate; D011188:Potassium; D002118:Calcium