Aluminum resistance in the Arabidopsis mutant alr-104 is caused by an aluminum-induced increase in rhizosphere pH.
A mechanism that confers increased Al resistance in the Arabidopsis thaliana mutant alr-104 was investigated. A modified vibrating microelectrode system was used to measure H+ fluxes generated along the surface of small Arabidopsis roots. In the absence of Al, no differences in root H+ fluxes between wild type and alr-104 were detected. However, Al exposure induced a 2-fold increase in net H+ influx in alr-104 localized to the root tip. The increased flux raised the root surface pH of alr-104 by 0.15 unit. A root growth assay was used to assess the Al resistance of alr-104 and wild type in a strongly pH-buffered nutrient solution. Increasing the nutrient solution pH from 4.4 to 4.5 significantly increased Al resistance in wild type, which is consistent with the idea that the increased net H+ influx can account for greater Al resistance in alr-104. Differences in Al resistance between wild type and alr-104 disappeared when roots were grown in pH-buffered medium, suggesting that Al resistance in alr-104 is mediated only by pH changes in the rhizosphere. This mutant provides the first evidence, to our knowledge, for an Al-resistance mechanism based on an Al-induced increase in root surface pH.
Degenhardt
J
J
United States Plant, Soil, and Nutrition Laboratory, United States Department of Agriculture-Agriculture Research Station, Cornell University, Ithaca, New York, 14853, USA.
Larsen
P B
PB
Howell
S H
SH
Kochian
L V
LV
D000535:Aluminum / Q000494:pharmacology*; D017360:Arabidopsis / Q000187:drug effects* / Q000235:genetics* / Q000378:metabolism; D004351:Drug Resistance / Q000235:genetics; D006863:Hydrogen-Ion Concentration / Q000187:drug effects; D017736:Ion-Selective Electrodes; D008839:Microelectrodes; D009154:Mutation; D018517:Plant Roots / Q000378:metabolism; D014732:Vibration
D000535:Aluminum