Expression of Arabidopsis CAX1 in tobacco: altered calcium homeostasis and increased stress sensitivity.
Calcium (Ca(2)+) efflux from the cytosol modulates Ca(2+) concentrations in the cytosol, loads Ca(2+) into intracellular compartments, and supplies Ca(2+) to organelles to support biochemical functions. The Ca(2+)/H(+) antiporter CAX1 (for CALCIUM EXCHANGER 1) of Arabidopsis is thought to be a key mediator of these processes. To clarify the regulation of CAX1, we examined CAX1 RNA expression in response to various stimuli. CAX1 was highly expressed in response to exogenous Ca(2+). Transgenic tobacco plants expressing CAX1 displayed symptoms of Ca(2+) deficiencies, including hypersensitivity to ion imbalances, such as increased magnesium and potassium concentrations, and to cold shock, but increasing the Ca(2+) in the media abrogated these sensitivities. Tobacco plants expressing CAX1 also demonstrated increased Ca(2+) accumulation and altered activity of the tonoplast-enriched Ca(2+)/H(+) antiporter. These results emphasize that regulated expression of Ca(2+)/H(+) antiport activity is critical for normal growth and adaptation to certain stresses.
Hirschi
K D
KD
Baylor College of Medicine, Department of Pediatrics, U.S. Department of Agriculture, Agricultural Research Service, Children's Nutrition Research Center, Houston, Texas 77030, USA. kendalh@bcm.tmc.edu
D017920:Antiporters / Q000235:genetics* / Q000378:metabolism*; D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000235:genetics* / Q000378:metabolism*; D027682:Cation Transport Proteins; D006706:Homeostasis; D015388:Organelles / Q000378:metabolism; D018517:Plant Roots / Q000378:metabolism; D030821:Plants, Genetically Modified; D010947:Plants, Toxic; D014026:Nicotiana / Q000235:genetics / Q000502:physiology*
D017920:Antiporters; D002135:Calcium-Binding Proteins; D027682:Cation Transport Proteins; C027614:calcium-hydrogen antiporters; D002118:Calcium