ARABIDOPSIS MUTANTS WITH INCREASED SENSITIVITY TO ALUMINUM

Al-sensitive (als) mutants of Arabidopsis were isolated and characteri zed with the aim of defining mechanisms of Al toxicity and resistance. Most als mutants selected on the basis of root growth sensitivity to Al were recessive, and together the mutants constituted eight compleme ntation groups. Also, in most als mutants, Al sensitivity appeared to be specific for Al relative to La (another trivalent cation), except a ls2, which was more sensitive to La than wild type. The tendency of ro ots on mutant seedlings to accumulate Al was examined by staining with morin and hematoxylin, dyes used to indicate the presence of Al. A si gnificant increase in morin staining was observed in als5, consistent with its increased sensitivity to Al. Unexpectedly, als7 and als4 show ed less morin staining, suggesting that the roots on these mutants acc umulate less Al than wild type after exposure to Al-containing solutio ns. Roots of wildtype seedlings produce callose in response to AlCl3 c oncentrations that inhibit root growth. Only als5 accumulated more cal lose than wild type in response to low levels (25 mu M) of AlCl3. Howe ver, als4 and als7 did not accumulate callose at this AlCl3 concentrat ion even though root growth was significantly inhibited. The lack of c allose accumulation in als4 and als7 suggests that there is not an obl igatory relationship between callose deposition and Al-induced inhibit ion of root growth.