Long-distance signaling within Coleus x hybridus leaves; mediated by changes in intra-leaf CO2?
Rapid long-distance signaling in plants can occur via several mechanisms, including symplastic electric coupling and pressure waves. We show here in variegated Coleus leaves a rapid propagation of electrical signals that appears to be caused by changes in intra-leaf CO2 concentrations. Green leaf cells, when illuminated, undergo a rapid depolarization of their membrane potential (Vm) and an increase in their apoplastic pH (pHa) by a process that requires photosynthesis. This is followed by a slower hyperpolarization of Vm and apoplastic acidification, which do not require photosynthesis. White (chlorophyll-lacking) leaf cells, when in isolated white leaf segments, show only the slow response, but when in mixed (i.e. green and white) segments, the rapid Vm depolarization and increase in pHa propagate over more than 10 mm from the green to the white cells. Similarly, these responses propagate 12-20 mm from illuminated to unilluminated green cells. The fact that the propagation of these responses is eliminated when the leaf air spaces are infiltrated with solution indicates that the signal moves in the apoplast rather than the symplast. A depolarization of the mesophyll cells is induced in the dark by a decrease in apoplastic CO2 but not by an increase in pHa. These results support the hypothesis that the propagating signal for the depolarization of the white mesophyll cells is a photosynthetically induced decrease in the CO2 level of the air spaces throughout the leaf.
Stahlberg
R
R
Department of Botany, University of Washington, Seattle 98195, USA. raista@u.washington.edu
Van Volkenburgh
E
E
Cleland
R E
RE
D002245:Carbon Dioxide / Q000378:metabolism*; D002473:Cell Wall / Q000378:metabolism; D002734:Chlorophyll / Q000378:metabolism / Q000528:radiation effects; D003624:Darkness; D006863:Hydrogen-Ion Concentration / Q000528:radiation effects; D019686:Lamiaceae / Q000378:metabolism* / Q000528:radiation effects; D008027:Light; D045342:Light-Harvesting Protein Complexes; D008564:Membrane Potentials / Q000502:physiology* / Q000528:radiation effects; D010788:Photosynthesis / Q000528:radiation effects; D045322:Photosynthetic Reaction Center Complex Proteins / Q000528:radiation effects; D018515:Plant Leaves / Q000378:metabolism* / Q000528:radiation effects; D006180:Proton-Translocating ATPases / Q000502:physiology / Q000528:radiation effects; D015398:Signal Transduction
D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D002734:Chlorophyll; D002245:Carbon Dioxide; D006180:Proton-Translocating ATPases