Alumunium tolerance in soybean: Protein profiles and accumulation of a1 in roots

Abstract

Four soybean genotypes were evaluated for their tolerance to aluminum toxicity using solution culture with pH 4.5. Based on the difference of root length, two genotypes were selected as Al-sensitive genotype (Lumut) and Al-tolerant genotype (Yellow Biloxi). The magnitude of the difference in Al tolerance between two genotypes was evidenced by the fact that at 0.7 mM Al the root length of Lumut was inhibited by 58%, whereas in Yellow Biloxi the inhibition was only 19.6%. Moreover, the hematoxylin staining indicated that Lumut accumulated more Al in the roots than Yellow Biloxi. This finding supports the proposed hypothesis of exclusion mechanisms of Al in the roots of tolerant soybean genotype. Characterization of total protein in the root tips (0.5-0.8 cm in length and adjacent 2 cm) by SDS-PAGE revealed the difference of protein profiles. In 0.7 mM Al exposure, only root tips of tolerant genotype could express a new protein band with molecular weight of approximately 79.8 kD, the protein of which disappeared when Al was removed from the treatment media. This phenomenon was found only in the protein characterization of root meristem with 0.5-0.8 cm in length, and not in the adjacent 2 cm of the root. Accumulation of these proteins in the presence of Al and their subsequent disappearance after removal Al from the growth medium suggested a possible involvement in Al resistance. These results are consistent with the hypothesis that these proteins are synthesized in the root tip region (0.5-0.8 cm) where the early effects of Al toxicity are often observed