Al-induced inhibition of root elongation in corn, Zea mays L is overcome by Si addition

The effect of silicic acid on Al-induced inhibition of root elongation was investigated in corn roots (Zea mays L. cv, golden cross bantam) in 100 mu M CaCl2 solution at pH 4.3. Twenty mu M Al inhibited root elongation (20 h) about 70%, however, inhibition was alleviated by addition of silicic acid. The alleviative effect increased with higher silicic acid concentrations. The concentration of Al3+ the toxic species, in solution was decreased to about 15, 10, and 5 mu M, respectively, from the initial concentration of 20 mu M by addition of silicic acid at 500, 1000, and 2000 mu M Si. Under the same concentration of Al3+, Al-induced inhibition of root elongation showed the same extent regardless of the addition of silicic acid or not by comparing 5 mu M Al treatment with 20 mu M Al + 2000 mu M Si treatment, and 10 mu M Al treatment with 20 mu M Al + 1000 mu M Si treatment. Viability of cells on the root tip surface was decreased by Al addition. Cell viability was not improved by addition of silicic acid under the same concentration of Al3+. All these facts suggest that the alleviative effect of silicic acid on Al toxicity resulted from decreasing toxic Al3+ concentration by forming Al-Si complexes rather than from other physiological effects of silicic acid in corn roots.