Differential accumulation of aluminum in root tips of soybean seedlings

In the present study, we investigated the sites of aluminum (Al) accumulation and its effects on the growth, morphology and nutritional status in root tips of soybean ( Glycine max L.) genotype Conquista. The seedlings were exposed to nutrient Clark solution, pH 4.0, with 0 (control) and 100 µM of Al for 24, 48 and 72 h. Our results showed an Al accumulation in the superficial layers of the root tip, such as the root cap cells, epidermis and cortex cells, and internally in the cell walls of the meristematic cells. The Al accumulation in the outer cells prevented the entry of this metal in the inner tissues. However, scanning electron micrographs showed damage in the external micromorphology of the root tips. This damage resulted in cellular disorganization in the root cap and epidermis cells leading to a reduction in Ca and Mg uptake. Despite that, there was no change in root growth. Taken together, our findings suggest that genotype Conquista has a capacity to avoid Al toxicity, probably by Al immobilization in the cell walls and in the external tissues of the root tip.