EFFECTS OF ALUMINUM ON THE GROWTH AND DISTRIBUTION OF CALCIUM IN ROOTS OF AN ALUMINUM-SENSITIVE CULTIVAR OF BARLEY (HORDEUM-VULGARE)

Aluminum-induced inhibition of root growth in the Al-sensitive cultiva r Kearney of barley (Hordeum vulgare L.) is the result of disruption o f both cell division in the meristematic region and cell expansion in the zone of elongation of the roots. In seedlings directly germinated in 50 mu M Al, inhibition of root growth is detected 48 h after initia tion of germination and it results primarily from the disruption of ce ll elongation. In seedlings germinated for 2 days under Al-free condit ions, inhibition of root growth is apparent 8 h after transfer to 50 m u M Al. In this instance, root growth inhibition is mainly the result of disruption of cell division in the meristematic region of the root. The calcium indicator dyes chlorotetracycline and Fluo-3 are used to study the distribution of intracellular calcium and its relationship t o aluminum phytotoxicity. Aluminum increases both chlorotetracycline a nd Fluo-3 fluorescence intensities. Fluorescence of the cytosolic calc ium indicator dye Fluo-3 increases primarily in the zone of elongation of the roots of seedlings directly germinated in 50 mu M aluminum. Th e increase in Fluo-3 fluorescence occurs concomitantly with major chan ges in both the length and width of the cells in the zone of elongatio n. The evidence suggests that changes in calcium homeostasis occurring in cells of the zone of elongation may be a major factor in the disru ption of cell expansion and consequently root growth in seedlings dire ctly germinated in 50 mu M aluminum.