Direct Measurement of Aluminum Uptake and Distribution in Single Cells of Chara corallina  

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 26 Al 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 g m Ϫ2 min Ϫ1 ), although transport across the plasma membrane was detectable (71-540 ng m Ϫ2 min Ϫ1 ) 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 {Al 3ϩ } 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 {Al 3ϩ } was reduced by complexing ligands. Cold temperature (4°C) 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.

Natural variation underlies alterations in Nramp aluminum transporter ( NRAT1 ) expression and function that play a key role in rice aluminum tolerance

“…The root, and more specifically, the root tip, is the primary site of Al toxicity, and the majority (∼90%) of the root Al resides in the cell wall (16,17). Al accumulation has been suggested to have a number of deleterious effects within the cell wall.…”

“…3 C and D). It has been well documented that most of the root Al (∼90%) occurs in the cell wall, presumably due in part to the cell wall's cation exchange capacity (16,17). For the smaller amount of Al that is transported into the root symplasm, most of this symplastic Al is believed to be sequestered in the vacuole, which occupies most (∼90%) of the volume of the root cell symplasm (5).…”

“…Because the majority of the Al in the root resides in the cell wall (16,17), the transport of cell wall Al into the root cell may function to reduce toxic levels of Al in the wall. It has been hypothesized that the Al transported into the cytoplasm by NRAT1 is subsequently sequestered in the vacuole by the tonoplast membrane Al transporter OsALS1 (5).…”

Inhibition of Phosphate Uptake in Corn Roots by Aluminum-Fluoride Complexes

“…Jones and Kochian, 1995;MacDiarmid and Gardner, 1998;Plieth et al, 1999;Sivaguru et al, 2000;Taylor et al, 2000;Pineros and Kochian, 2001), relatively little attention has been directed toward the AlF x phytotoxicity mechanism. On the other hand, in enzymology, the properties of fluoroaluminates have been explored extensively during the last two decades.…”

Identification of the tri-Al tricitrate complex in Plantago almogravensis by hydrophilic interaction LC with parallel ICP-MS and electrospray Orbitrap MS/MS detection

“…By comparing the elution time of this Al-complex with the signal of other elements a correlation was observed with 31 P (Fig. 1D) 32 Because it was not expected for plants to have specific transporters for a non-essential element, it was hypothesized that Al 3+ could permeate divalent cation channels. 25 However, a specific Al transporter named Nrat1 (Nramp aluminum transporter 1) was recently discovered in rice.…”