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CO2 and Ion Transport Via Plant Aquaporins

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CO2 and Ion Transport Via Plant Aquaporins CO2 and Ion Transport via Plant Aquaporins Zhao Manchun School of Agriculture, Food and Wine The University of Adelaide This thesis is submitted to the University of Adelaide in accordance with the requirements of the degree of PhD September 2013 Table of Contents Chapter 1 General Introduction ................................................................................................................ 1 1.1 CO2 transport ................................................................................................................................. 2 1.1.1 Resistance along the CO2 pathway inside leaves .................................................................... 2 1.1.2 CO2 diffusion through biological membranes ......................................................................... 4 1.2 General features of Aquaporins ................................................................................................... 12 1.2.1 Aquaporin classification, and sub-cellular and tissue localization ........................................ 13 1.2.2 Structural characteristics of aquaporins ................................................................................ 15 1.3 Aquaporin functions ..................................................................................................................... 16 1.3.1 Water uptake ......................................................................................................................... 16 1.3.2 Non-charged small neutral solute transport .......................................................................... 19 1.3.3 Gas transport ......................................................................................................................... 21 1.3.4 Ion transport via aquaporins .................................................................................................. 23 1.4 Aquaporins blockers .................................................................................................................... 24 1.5 Interaction between aquaporins ................................................................................................... 26 1.6 Conclusion and project aims ........................................................................................................ 28 Chapter 2 Water and CO2 transport across leaf plasma membranes ...................................................... 31 2.1 Introduction .................................................................................................................................. 31 2.2 Materials and Methods ................................................................................................................ 34 2.2.1 Plant material and growth conditions .................................................................................... 34 2.2.2 Stomatal conductance measurement ..................................................................................... 34 2.2.3 Vesicle isolation .................................................................................................................... 35 2.2.4 Vesicle size determination .................................................................................................... 37 2.2.5 Water permeability (Pos) determination ................................................................................ 38 2.2.6 CO2 uptake experiments ........................................................................................................ 40 2.2.7 Final intracellular pH calculation .......................................................................................... 42 2.2.8 Inhibitors ............................................................................................................................... 43 2.2.9 Arabidopsis vesicles .............................................................................................................. 43 2.3 Results .......................................................................................................................................... 44 2.3.1 Water permeability (Pos) determination ................................................................................ 44 2.3.2 CO2 Permeability .................................................................................................................. 46 2.3.3 Stomatal conductance measurement ..................................................................................... 57 2.3.4 Water permeability of dark and drought treated peas ........................................................... 58 2.3.5 Arabidopsis vesicles .............................................................................................................. 61 2.3.6 The relationship between water permeability and CO2 permeability .................................... 63 2.4 Discussion .................................................................................................................................... 65 I 2.4.1 CO2 pathway in plants and mesophyll conductance ............................................................. 65 2.4.2 Do aquaporins facilitate CO2 transport ................................................................................. 65 2.4.3 High water permeability indicating high aquaporins activity ............................................... 67 2.4.4 The acidification rate inside vesicles .................................................................................... 67 2.4.5 Carbonic anhydrase .............................................................................................................. 68 2.4.6 Pure biophysical point of view ............................................................................................. 69 2.4.7 Aquaporin inhibitor effects ................................................................................................... 71 2.4.8 Selecting the most appropriate temperature to measure CO2 permeability .......................... 72 2.4.9 Correlation of water permeability and CO2 permeability and conclusion ............................ 72 Chapter 3 Functional Characterisation of Arabidopsis aquaporins ....................................................... 75 3.1 Introduction ................................................................................................................................. 75 3.2. Materials and Methods ............................................................................................................... 81 3.2.1 Solutions, media and bacterial transformation ..................................................................... 81 3.2.2 Cloning Arabidopsis PIP1s and PIP2s into pEntry TOPO® vector .................................... 82 3.2.3 Cloning Arabidopsis PIP1s and PIP2s into oocyte expression vector ................................. 85 3.2.4 Site-directed mutagenesis of AtPIP2;1 (G100W) ................................................................ 87 3.2.5 cRNA transcription ............................................................................................................... 88 3.2.6 cRNA purity check and concentration quantification ........................................................... 90 3.2.7 Harvesting oocytes ............................................................................................................... 91 3.2.8 Expression of Arabidopsis aquaporins in Xenopus oocytes ................................................. 92 3.2.9 Oocytes swelling assay ......................................................................................................... 92 3.3 Results .......................................................................................................................................... 94 3.3.1 Transcription of cRNA and cRNA concentration quantification ......................................... 94 3.3.2 Aquaporin activity—the swelling assay ............................................................................... 96 3.3.3 Expression of PIPs alone or in PIP1-PIP2 combinations in Xenopus oocytes ...................... 99 3.3.4 Mutant Atpip2;1 .................................................................................................................. 101 3.3.5 Effect of silver-sulfadiazine on aquaporin water permeability ........................................... 103 3.4 Discussion .................................................................................................................................. 104 3.4.1 Water permeability of AtPIP1s and AtPIP2s ...................................................................... 104 3.4.2 Interaction between AtPIP1s and AtPIP2s ......................................................................... 106 3.4.3 Aquaporin inhibition ........................................................................................................... 108 Chapter 4 Ion Currents Induced by AtPIP2;1 in Xenopus Oocytes ..................................................... 111 4.1 Introduction ............................................................................................................................... 111 4.2 Materials and Methods .............................................................................................................. 114 4.2.1 Oocytes harvesting and cRNA injection ............................................................................. 114 4.2.2 cRNA synthesis .................................................................................................................
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