ALTERATIONS IN THE CYTOSKELETON ACCOMPANY ALUMINUM-INDUCED GROWTH-INHIBITION AND MORPHOLOGICAL-CHANGES IN PRIMARY ROOTS OF MAIZE

Although Al is one of the major factors limiting crop production, the mechanisms of toxicity remain unknown. The growth inhibition and swell ing of roots associated with Al exposure suggest that the cytoskeleton may be a target of Al toxicity. Using indirect immunofluorescence mic roscopy, microtubules and microfilaments in maize (Zea mays L.) roots were visualized and changes in their organization and stability correl ated with the symptoms of Al toxicity. Growth studies showed that the site of Al toxicity was associated with the elongation zone. Within th is region, Al resulted in a reorganization of microtubules in the inne r cortex. However, the orientation of microtubules in the outer cortex and epidermis remained unchanged even after chronic symptoms of toxic ity were manifest. Auxin-induced reorientation and fold-induced depoly merization of microtubules in the outer cortex were blocked by Al pret reatment. These results suggest that Al increased the stability of mic rotubules in these cells. The stabilizing effect of Al in the outer co rtex coincided with growth inhibition. Reoriented microfilaments were also observed in Al-treated roots, and Al pretreatment minimized cytoc halasin B-induced microfilament fragmentation. These data show that re organization and stabilization of the cytoskeleton are closely associa ted with Al toxicity in maize roots.