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Al-induced, 51-kilodalton, membrane-bound proteins are associated with resistance to Al in a segregating population of wheat

Taylor, G.J., Basu, A., Basu, U., Slaski, J.J., Zhang, G., Good, A.
Plant physiology 1997 v.114 no.1 pp. 363-372
cultivars, sulfur, protein synthesis, dose response, quantitative analysis, callose, phytotoxicity, radiolabeling, stress response, cytosol, microsomes, Triticum aestivum, aluminum, mitochondria, tonoplast, genetic variation, plasma membrane, genotype, protein composition
Incorporation of 35S into protein is reduced by exposure to Al in wheat (Triticum aestivum), but the effects are genotype-specific. Exposure to 10 to 75 micromolars Al had little effect on 35S incorporation into total protein, nuclear and mitochondrial protein, microsomal protein, and cytosolic protein in the Al-resistant cultivar PT741. In contrast, 10 micromolars Al reduced incorporation by 21 to 38% in the Al-sensitive cultivar Katepwa, with effects becoming more pronounced (31-62%) as concentrations of Al increased. We previously reported that a pair of 51-kD membrane-bound proteins accumulated in root tips of PT741 under conditions of Al stress. We now report that the 51-kD band is labeled with 35S after 24 h of exposure to 75 micromolars Al. The specific induction of the 51-kD band in PT741 suggested a potential role of one or both of these proteins in mediating resistance to Al. Therefore, we analyzed their expression in single plants from an F2 population arising from a cross between the PT741 and Katepwa cultivars. Accumulation of 1,3-beta-glucans (callose) in root tips after 24 h of exposure to 100 micromolars Al indicated that this population segregated for Al resistance in about a 3:1 ratio. A close correlation between resistance to Al (low callose content of root tips) and accumulation of the 51-kD band was observed, indicating that at least one of these proteins cosegregates with the Al-resistance phenotype. As a first step in identifying a possible function, we have demonstrated that the 51-kD band is most clearly associated with the tonoplast. Whereas Al has been reported to stimulate the activity of the tonoplast H+-ATPase and H+-PPase, antibodies raised against these proteins did not cross-react with the 51-kD band. Efforts are now under way to purify this protein from tonoplast-enriched fractions.