title: Organelle-localized potassium transport systems in plants.
abstract: Some intracellular organelles found in eukaryotes such as plants have arisen through the endocytotic engulfment of prokaryotic cells. This accounts for the presence of plant membrane intrinsic proteins that have homologs in prokaryotic cells. Other organelles, such as those of the endomembrane system, are thought to have evolved through infolding of the plasma membrane. Acquisition of intracellular components (organelles) in the cells supplied additional functions for survival in various natural environments. The organelles are surrounded by biological membranes, which contain membrane-embedded K(+) transport systems allowing K(+) to move across the membrane. K(+) transport systems in plant organelles act coordinately with the plasma membrane intrinsic K(+) transport systems to maintain cytosolic K(+) concentrations. Since it is sometimes difficult to perform direct studies of organellar membrane proteins in plant cells, heterologous expression in yeast and Escherichia coli has been used to elucidate the function of plant vacuole K(+) channels and other membrane transporters. The vacuole is the largest organelle in plant cells; it has an important task in the K(+) homeostasis of the cytoplasm. The initial electrophysiological measurements of K(+) transport have categorized three classes of plant vacuolar cation channels, and since then molecular cloning approaches have led to the isolation of genes for a number of K(+) transport systems. Plants contain chloroplasts, derived from photoautotrophic cyanobacteria. A novel K(+) transport system has been isolated from cyanobacteria, which may add to our understanding of K(+) flux across the thylakoid membrane and the inner membrane of the chloroplast. This chapter will provide an overview of recent findings regarding plant organellar K(+) transport proteins.
authors.affiliation: Department of Biomolecular Engineering, Graduate School of Engineering, Tohoku University, Aobayama 6-6-07, Sendai 980-8579, Japan.
authors.forename: Shin
authors.initials: S
authors.lastname: Hamamoto
authors.affiliation: Department of Biomolecular Engineering, Graduate School of Engineering, Tohoku University, Aobayama 6-6-07, Sendai 980-8579, Japan. Electronic address: uozumi@biophy.che.tohoku.ac.jp.
authors.forename: Nobuyuki
authors.initials: N
authors.lastname: Uozumi
mesh_terms: D001692:Biological Transport; D002736:Chloroplasts / Q000378:metabolism; D000458:Cyanobacteria / Q000378:metabolism*; D008954:Models, Biological; D015388:Organelles / Q000378:metabolism*; D010937:Plant Growth Regulators / Q000378:metabolism; D010940:Plant Proteins / Q000378:metabolism; D010944:Plants / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism*; D015221:Potassium Channels / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D014617:Vacuoles / Q000378:metabolism
chemical_list: D010937:Plant Growth Regulators; D010940:Plant Proteins; D015221:Potassium Channels; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium
keywords: Cyanobacteria; Organelle potassium channels; TPK; Vacuolar channels