Sorption of aluminum to plasma membrane vesicles isolated from roots of Scout 66 and Atlas 66 cultivars of wheat.

摘要

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 the Al3+-sensitive cultivar Scout 66 and the Al3+-tolerant cultivar Atlas 66of wheat (Triticum aestivum). Vesicles from cv. Scout 66 root tips sorbed more Al than vesicles prepared from any other source. The intrinsic surface-charge density of vesicles isolated from Scout 66 was 26% more negative than vesicles from Atlas 66 (-37.2 versus -29.5 millicoulombs m-2). Growth experiments indicated that Scout 66 is slightly more sensitive to La3+ than Atlas 66, that the cultivars are equally sensitive to H+, and that Atlas 66 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 Atlas 66. Using a newly developed Gouy-Chapman-Stern model for ion sorption to the PM together with growth-response curves, it was estimated thatthe difference in surface-charge density can account for the slightly greater sensitivity of Scout 66 to cationic toxicants and the slightly greater sensitivity of Atlas 66 to anionic toxicants. It is concluded that 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 Atlas 66 root tips that reduce the amount of Al3+ that canreach the PM.