SREL Reprint #2458

Direct measurement of aluminum uptake and distribution in single cells of Chara corallina

Gregory J. Taylor1, Julie L. McDonald-Stephens1, Douglas B. Hunter2, Paul M. Bertsch2, David Elmore3,
Zdenko Rengel4, and Robert J. Reid5

1Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada T6G 2E9
2Advanced Analytical Center for Environmental Studies, Savannah River Ecology Laboratory,
The University of Georgia, Aiken, South Carolina 29801
3Purdue Rare Isotope Measurement Laboratory, Purdue University, West Lafayette, Indiana 47907-1396
4Soil Science and Plant Nutrition Faculty of Agriculture, University of Western Australia,
Perth, Western Australia 6907, Australia
5Department of Botany, University of Adelaide, Adelaide, South Australia 5005, Australia

Abstract: Quantitative information on the uptake and distribution of Al at the cellular level is required to understand mechanisms of Al toxicity, but direct measurement of uptake across the plasma membrane has remained elusive. We measured rates of Al transport across membranes in single cells of Chara corallina using the rare 26Al isotope, an emerging technology (accelerator mass spectrometry), and a surgical technique for isolating subcellular compartments. Accumulation of Al in the cell wall dominated total uptake (71-318 µg m-2 min-1), although transport across the plasma membrane was detectable (71-540 ng m-2 min-1) within 30 min of exposure. Transport across the tonoplast was initially negligible, but accelerated to rates approximating uptake across the plasma membrane. The avacuolate protoplasm showed signs of saturation after 60 min, but continued movement across the plasma membrane was supported by sequestration in the vacuole. Saturation of all compartments was observed after 12 to 24 h. Accumulation of Al in the cell wall reflected variation in {Al3+} induced by changes in Al supply or complexing ligands, but was unaffected by pH. In contrast, transport across the plasma membrane peaked at pH 4.3 and increased when {Al3+} was reduced by complexing ligands. Cold temperature (4ºC) reduced accumulation in the cell wall and protoplasm, whereas 2,4-dinitrophenol and m-chlorocarbonylcyanidephenyl hydrazone increased membrane transport by 12- to 13-fold. Our data suggest that the cell wall is the major site of Al accumulation. Nonetheless, membrane transport occurs within minutes of exposure and is supported by subsequent sequestration in the vacuole. The rapid delivery of Al to the protoplasm suggests that intracellular lesions may be possible.

SREL Reprint #2458

Taylor, G. J., J. L. McDonald-Stephens, D. B. Hunter, P. M. Bertsch, D. Elmore, Z. Rengel, and R. J. Reid. 2000. Direct measurement of aluminum uptake and distribution in single cells of Chara corallina. Plant Physiology 123:987-996.

This information was provided by the University of Georgia's Savannah River Ecology Laboratory (srel.uga.edu).