PLANT PHYSIOLOGY , Vol 115, Issue 3 1119-1125, Copyright © 1997 by American Society of Plant Biologists
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WHOLE PLANT, ENVIRONMENTAL, AND STRESS PHYSIOLOGY |
Sorption of Aluminum to Plasma Membrane Vesicles Isolated from Roots of Scout 66 and Atlas 66 Cultivars of Wheat
U. Yermiyahu, D. K. Brauer and T. B. Kinraide
Appalachian Soil and Water Conservation Research Laboratory, Agricultural Research Service, United States Department of Agriculture, Beaver, West Virginia 25813-0400
To further elucidate the mechanisms of differential genotypic tolerance to
Al, plasma membrane (PM) vesicles were isolated from whole roots, root
tips, and tipless roots of Al3+-sensitive and Al3+-tolerant cultivars (cv)
of wheat (Triticum aestivum L. cv Scout 66 and cv Atlas 66, respectively).
Vesicles from cv Scout root tips sorbed more Al than vesicles prepared from
any other source. The intrinsic surface-charge density of vesicles isolated
from cv Scout was 26% more negative than vesicles from cv Atlas (-37.2
versus -29.5 millicoulombs m-2). Growth experiments indicated that cv Scout
is slightly more sensitive to La3+ than is cv Atlas, that the cultivars are
equally sensitive to H+, and that cv Atlas is slightly more sensitive to
SeO42-. The difference in sensitivity to Al3+ was very large; for a 50%
inhibition, a 16-fold greater activity of Al3+ was required for cv Atlas.
Using a newly developed Gouy-Chapman-Stern model for ion sorption to the PM
together with growth-response curves, we estimate that the difference in
surface-charge density can account for the slightly greater sensitivity of
cv Scout to cationic toxicants and the slightly greater sensitivity of cv
Atlas to anionic toxicants. According to our estimates the differences in
PM surface negativity and Al sorptive capacity probably account for some of
the difference in sensitivity to Al3+, but the greater part of the
difference probably arises from other tolerance mechanisms expressed in cv
Atlas root tips that reduce the amount of Al3+ that can reach the PM.
