Responses of photosynthetic electron transport in stomatal guard cells and mesophyll cells in intact leaves to light, CO2, and humidity.
High-resolution images of the chlorophyll fluorescence parameter Fq'/Fm' from attached leaves of commelina (Commelina communis) and tradescantia (Tradescantia albiflora) were used to compare the responses of photosynthetic electron transport in stomatal guard cell chloroplasts and underlying mesophyll cells to key environmental variables. Fq'/Fm' estimates the quantum efficiency of photosystem II photochemistry and provides a relative measure of the quantum efficiency of non-cyclic photosynthetic electron transport. Over a range of light intensities, values of Fq'/Fm' were 20% to 30% lower in guard cell chloroplasts than in mesophyll cells, and there was a close linear relationship between the values for the two cell types. The responses of Fq'/Fm' of guard and mesophyll cells to changes of CO2 and O2 concentration were very similar. There were similar reductions of Fq'/Fm' of guard and mesophyll cells over a wide range of CO2 concentrations when the ambient oxygen concentration was decreased from 21% to 2%, suggesting that both cell types have similar proportions of photosynthetic electron transport used by Rubisco activity. When stomata closed after a pulse of dry air, Fq'/Fm' of both guard cell and mesophyll showed the same response; with a marked decline when ambient CO2 was low, but no change when ambient CO2 was high. This indicates that photosynthetic electron transport in guard cell chloroplasts responds to internal, not ambient, CO2 concentration.
Lawson
Tracy
T
Department of Biological Sciences, University of Essex, Colchester, CO4 3SQ United Kingdom.
Oxborough
Kevin
K
Morison
James I L
JI
Baker
Neil R
NR
D000465:Algorithms; D002245:Carbon Dioxide / Q000494:pharmacology*; D002734:Chlorophyll / Q000378:metabolism / Q000528:radiation effects; D002736:Chloroplasts / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D004579:Electron Transport / Q000187:drug effects / Q000528:radiation effects; D008027:Light; D045342:Light-Harvesting Protein Complexes; D019684:Magnoliopsida / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D010100:Oxygen / Q000494:pharmacology; D010788:Photosynthesis / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D045322:Photosynthetic Reaction Center Complex Proteins / Q000378:metabolism* / Q000528:radiation effects; D045332:Photosystem II Protein Complex; D018515:Plant Leaves / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D014867:Water / Q000494:pharmacology*
D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D014867:Water; D002734:Chlorophyll; D002245:Carbon Dioxide; D010100:Oxygen