Aluminium distribution in soybean root tip for a short time Al treatment

Using the lumogallion staining method which we developed (Kataoka et al. 1997a), Al movement in soybean (Glycine max. (L.)Merr. cv. Tsurunoko) root tips treated for a short time was studied. We have indicated that the majority of Al accumulated in the root was found between 0 and 2 mm from the root apex within 2 h (Kataoka et al. 1997a, b). In the study presented here two-day seedlings of the soybean were treated with 50 μmol/L AlCl₃ (pH 4.4), including 0.2 mmol/L CaCl₂, for 1 h, and Al accumulation in the root sections at both 1 and 2 mm apart from root apex was analyzed by a confocal laser microscopy. Although the early indicators, callose induction and the decrease of growth recovery, were not observed in the root when treated for 15 min, a trace amount of Al was already incorporated into the nucleus of cells and the middle tissue of the root. The non-toxic level of Al was more rapidly absorbed than previously thought. The initial increase of callose accumulation and the reduction of the growth recovery were found after 30 min. Therefore, the difference between Al accumulation profiles of 15 and 30 min was analyzed to find out what triggered a toxic Al effect. Increase of Al accumulation in whole root tissue was observed in the root sections, at both 1 and 2 mm from the root apex, and the greatest amount of Al was found in the cytoplasm of the outer cortex, 1 mm away from the root apex. These results are consistent with the fact that Al exclusion from root tip cells is an important mechanism of Al tolerance.