The kinetics of aluminum action on the elongation of primary roots of Zea Mays

Aluminum (Al) is a phytotoxic element that inhibits root elongation. We used a root auxanometer to examine the kinetics of Al action on primary roots of maize (cv Merit) growing in oxygenated 0.4 mM CaCl{sub 2} adjusted to pH 4.5. One mM Al promoted elongation almost immediately (< 2 min). Within 30-45 min the rate of elongation began to decline and decreased to zero within 36-45 h. Exposure to 10 {mu}M Al also promoted elongation almost immediately; however, the new steady rate was achieved only after about 25 min. When roots were decapped prior to exposure to 10 {mu}M Al, elongation was still promoted but the new steady rate of elongation was not attained until 1.5 h after addition of Al. The results indicate that Al initially promotes root elongation and that the root cap is important for rapid responses to Al.