Effect of Al³⁺ toxicity on release and viability of soybean root border cells

Experiments were carried out to examine Al3+ effects on release of border cells in situ around root tips or in suspension by comparing responses of two soybean ［Glycine max (L.) Merr.］ cultivars (Al-resistance Zhechun No. 2 and Al-sensitive Huachun No.18) known to differ in Al resistance at the whole-root level. Both cultivars' border cells in situ exposed to 0, 100, 200 μmol/L Al3+ dispersed readily into suspension, however, border cells of Huachun No.18 and roots clumped together and did not dispense at 300 μmol/L and 400 μmol/L Al3+, respectively. Al3+ treatment significantly decreased cell viability, cell death was found during a 1-6 h Al3+ exposure time at a concentration of 100 μmol/L, and the cell death was greatest after 6 h Al3+ treatment. Toxic effect on cell viability was higher in Huachun No.18 than that of Zhuchun No.2 during the whole suspension culture. Cell survival percentage of border cells in vitro dropped greatly when treated with 100 μmol/L Al3+. When the treatment level increased to 400 μmol/L Al3+, cell survival percentage of Zhechun No. 2 and Huachun No.18 were only 31.6% and 26.2%, respectively. These results indicate that Al3+ solution may affect release of border cells from root tip, and significant reduce their survival rate, with the highest toxicity effect occurring after 6 h. These responses were different with cultivars, and the differences were largest at 6 h after treatment. This Al-resistance mechanism by releasing border cells may act as one of the purported conditioning factors thought to affect the vitality of in vitro cultures.