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 μM CaCl₂ solution at pH 4.3. Twenty μM 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 μM, respectively, from the initial concentration of 20 μM by addition of silicic acid at 500, 1000, and 2000 μM 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 μM Al treatment with 20 μM Al + 2000 μM Si treatment, and 10 μM Al treatment with 20 μM Al +1000 μM 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.