Aluminum distribution and viability of plant root and cultured cells (Reprinted from Plant nutrition for sustainable food production and environment, 1997)

Viability and growth recovery in response to aluminum (Al) toxicity for tobacco (Nicotina tabacum L.) BY-2 cells and soybean (Glycine max (L.) Merr. cv. Tsurunoko) roots were investigated. When tobacco BY-2 cells were treated with 100 mu M AlCl3 at pH 5.0 for 15 hours, Al accumulation was observed in the cell further into nucleus. However, there was no decrease in viability and growth recovery compared with those of control cells. In the case of soybean roots, Al accumulation was observed in root cap. epidermis and outer cortex after treatment with 200 mu M AlCl3 (pH 4.5) solution containing 0.2 mM CaCl2 for 2 hours through confocal laser microscopic observation. After 4 hours, Al accumulation was found in the outer cortex of the elongation zone, in which Al remained even after washing with citrate. Though no change was found in viability and growth recovery until 2 hours of treatment, after 4 hours, both viability and the growth recovery decreased drastically. The Al in cell walls after 4 hours of treatment suggested that Al forms strong bonds in cortex cells, which this resulted in the destruction of the epidermis and cortex by inhibiting the elongation of each cell. The sensitivity of Al staining method was studied further using colorimetric reagents, aluminon, hematoxylin and pyrocatechol violet, as well as fluorescence ones, lumogallion and morin. Among the reagents investigated, lumogallion and morin showed higher sensitivity in cultured cells for an optical microscopic observation. However, in the case of the confocal laser microscope, which is suitable to observe Al distribution in intact roots, the lumogallion staining method showed much higher sensitivity than that of morin.