AL INHIBITS BOTH SHOOT DEVELOPMENT AND ROOT-GROWTH IN ALS3, AN AL-SENSITIVE ARABIDOPSIS MUTANT

In als3, an Al-sensitive Arabidopsis mutant, shoot development and roo t growth are sensitive to Al. Mutant als3 seedlings grown in an Al-con taining medium exhibit severely inhibited leaf expansion and root grow th. In the presence of Al, unexpanded leaves accumulate callose, an in dicator of Al damage in roots. The possibility that the inhibition of shoot development in als3 is due to the hyperaccumulation of Al in thi s tissue was examined. However, it was found that the levels of Al tha t accumulated in shoots of als3 are not different from the wild type. The inhibition of shoot development in als3 is not a consequence of no nspecific damage to roots, because other metals (e.g. LaCl3 or CuSO4) that strongly inhibit root growth did not block shoot development in a ls3 seedlings. Al did not block leaf development in excised als3 shoot s grown in an Al-containing medium, demonstrating that the Al-induced damage in als3 shoots was dependent on the presence of roots. This sug gests that Al inhibition of als3 shoot development may be a delocalize d response to Al-induced stresses in roots following Al exposure.