Association between water and carbon dioxide transport in leaf plasma membranes: assessing the role of aquaporins.
The role of some aquaporins as CO2permeable channels has been controversial. Low CO2permeability of plant membranes has been criticized because of unstirred layers and other limitations. Here we measured both water and CO2permeability (Pos, PCO2) using stopped flow on plasma membrane vesicles (pmv) isolated from Pisum sativum (pea) and Arabidopsis thaliana leaves. We excluded the chemical limitation of carbonic anhydrase (CA) in the vesicle acidification technique for PCO2using different temperatures and CA concentrations. Unstirred layers were excluded based on small vesicle size and the positive correlation between vesicle diameter and PCO2. We observed high aquaporin activity (Pos0.06 to 0.22 cm s-1) for pea pmv based on all the criteria for their function using inhibitors and temperature dependence. Inhibitors of Posdid not alter PCO2. PCO2ranged from 0.001 to 0.012 cm s-1(mean 0.0079 + 0.0007 cm s-1) with activation energy of 30.2 kJ mol-1. Intrinsic variation between pmv batches from normally grown or stressed plants revealed a weak (R2= 0.27) positive linear correlation between Posand PCO2. Despite the low PCO2, aquaporins may facilitate CO2transport across plasma membranes, but probably via a different pathway than for water.
Australian Research Council Centre of Excellence in Plant Energy Biology, School of Agriculture, Food and Wine, Waite Research Institute, University of Adelaide, Glen Osmond, South Australia, 5064, Australia.
Manchun
M
Zhao
Australian Research Council Centre of Excellence in Plant Energy Biology, School of Agriculture, Food and Wine, Waite Research Institute, University of Adelaide, Glen Osmond, South Australia, 5064, Australia.
Hwei-Ting
HT
Tan
Australian Research Council Centre of Excellence in Plant Energy Biology, School of Agriculture, Food and Wine, Waite Research Institute, University of Adelaide, Glen Osmond, South Australia, 5064, Australia.
Johannes
J
Scharwies
Australian Research Council Centre of Excellence in Plant Energy Biology, School of Agriculture, Food and Wine, Waite Research Institute, University of Adelaide, Glen Osmond, South Australia, 5064, Australia.
Kara
K
Levin
Division of Plant Sciences, Research School of Biology, The Australian National University, Canberra, Australian Capital Territory, 0200, Australia.
John R
JR
Evans
Australian Research Council Centre of Excellence in Plant Energy Biology, School of Agriculture, Food and Wine, Waite Research Institute, University of Adelaide, Glen Osmond, South Australia, 5064, Australia.
Stephen D
SD
Tyerman
D000086:Acetazolamide / Q000494:pharmacology; D020346:Aquaporins / Q000378:metabolism*; D017360:Arabidopsis / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000378:metabolism; D002245:Carbon Dioxide / Q000378:metabolism*; D002257:Carbonic Anhydrase Inhibitors / Q000494:pharmacology; D002462:Cell Membrane / Q000378:metabolism*; D018532:Pisum sativum / Q000378:metabolism; D018515:Plant Leaves / Q000187:drug effects / Q000378:metabolism*; D010940:Plant Proteins / Q000378:metabolism; D013411:Sulfadiazine / Q000494:pharmacology; D014867:Water / Q000378:metabolism*
D020346:Aquaporins; D029681:Arabidopsis Proteins; D002257:Carbonic Anhydrase Inhibitors; D010940:Plant Proteins; C491680:plasma membrane intrinsic protein 2 Arabidopsis; D014867:Water; D013411:Sulfadiazine; D002245:Carbon Dioxide; D000086:Acetazolamide