Frans J Maathuis

5.1 Introduction 75

5.1.1 Plant solutes 76

5.1.2 Definitions and terminology 76

5.1.3 Some formalisms 79

5.2 Passive transport 81

5.2.1 Diffusion through membranes 81

5.2.2 Facilitated diffusion through carriers 82

5.2.3 Transport through ion channels 83

5.2.3.1 Potassium channels 84

5.2.3.2 Calcium channels 85

5.2.3.3 Non-selective ion channels 85

5.2.3.4 Chloride channels 85

5.2.4 Transport through water channels 85

5.3 Primary active transport 87

5.3.1 Primary proton pumps 87

5.3.1.1 P-type ATPases 88

5.3.1.2 V-type ATPases 89

5.3.1.3 The pyrophosphatase 90

5.3.2 Primary pumps involved in metal transport 90

5.3.2.2 Heavy metal ATPases 91

5.3.3 ABC transporters 92

5.4 Secondary active transport 92

5.4.1 Potassium uptake 93

5.4.2 Nitrate transport 94

5.4.3 Sodium efflux 95

5.4.4 Non H+-coupled secondary transport 95

5.5 Concluding remarks 96

References 96

6 Regulation of ion transporters 99

ANNA AMTMANN and MICHAEL R. BLATT

6.1 Introduction 99

6.2 Physiological situations requiring the regulation of ion transport 99

6.2.1 Change of cell volume 99

6.2.2 Nutrient acquisition 102

6.2.3 Stress responses 106

6.3 Molecular mechanism of regulation 107

6.3.1 Transcriptional regulation 108

6.3.2 Post-translational regulation 109

6.3.2.1 Autoinhibition 109

6.3.2.2 14-3-3 proteins 111

6.3.2.3 Calmodulin 113

6.3.2.4 Cyclic nucleotides 114

6.3.2.5 Heteromerisation 116

6.4 Traffic of ion transporters 117

6.5 Conclusions and outlook 120 References 120

7 Intracellular transport: solute transport in chloroplasts, mitochondria, peroxisomes and vacuoles, and between organelles 133

KATRIN PHILIPPAR and J√úRGEN SOLL

7.1 Introduction 133 7.1.1 Research to identify solute transport proteins in plant organelles 133 7.1.1.1 Benefits of a model plant: Arabidopsis thaliana 134

7.2 Chloroplasts 136

7.2.1 The function of plastids 137

7.2.2 Transport across the outer envelope: general diffusion or regulated channels? 137

7.2.2.1 A porin in the outer envelope of plastids? 138

7.2.2.2 OEPs, a family of channels with substrate specificity 138

7.2.2.3 Outer membrane channels and porins: evolutionary aspects in chloroplasts and mitochondria 142

7.2.3 Transport across the inner envelope: phosphate translocators, major facilitators and carriers 142 7.2.3.1 The phosphate translocator family 142

7.2.3.2 Major-facilitator-mediated transport 144

7.2.3.3 Carriers in the inner envelope of plastids 146 7.2.4 Transport across the inner envelope: ABC transporters and ion transport 147

7.2.4.1 ABC transporters 147

7.2.4.2 Ion transport 149

7.2.4.3 Transport of metal ions 150

7.3 Mitochondria 153

7.3.1 The function of plant mitochondria 153

7.3.2 Transport across the outer membrane: the porin VDAC 154

7.3.3 Transport across the inner membrane: carriers 156

7.3.3.1 Transporters involved in ATP production 156

7.3.3.2 Carriers for transport of TCA cycle intermediates 158

7.3.3.3 Amino acid transport across mitochondrial membranes 159

7.3.3.4 Carriers involved in j-oxidation of fatty acids 160

7.3.4 Transport across the inner membrane: ABC

transporters and ion channels 160

7.3.4.1 ABC transporters 160

7.3.4.2 Ion channels 161

7.4 Peroxisomes 162

7.4.1 Function of peroxisomes in plant metabolism 163

7.4.2 Solute transport across the peroxisomal membrane 163

7.4.2.1 A porin in the peroxisomal membrane 163

7.4.2.2 Specific transport proteins in the peroxisomal membrane 165

7.5 Photorespiration: transport between plastids, mitochondria and peroxisomes 166

7.6 Vacuoles 167

7.6.1 Generating a pH gradient across the tonoplast:

H+-ATPase and H+-pyrophosphatase 168

7.6.2 Transport of malate and sucrose across the tonoplast 170

7.6.2.1 Malate 170

7.6.2.2 Sucrose 171

7.6.3 Aquaporins and ABC transporter in the tonoplast 171

7.6.3.1 Aquaporins in the vacuole are tonoplast-intrinsic proteins 171

7.6.3.2 ABC transporters in the tonoplast 172

7.6.4 Ion transport 173

7.6.4.1 Ion channels 173

7.6.4.2 Calcium, sodium and magnesium uptake involves active transport 175

7.6.4.3 Transport of transition metals 177 References 178

8 Ion uptake by plant roots 193

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