No abstract

Phytotoxicity of aluminum is characterized by a rapid inhibition of root elongation at micromolar concentrations, however, the mechanisms primarily responsible for this response are not well understood. We investigated the effect of Al on the viscosity and elasticity parameters of root cell wall by a creep-extension analysis in two cultivars of wheat (Triticum aestivum L.) differing in Al resistance. The root elongation and both viscous and elastic extensibility of cell wall of the root apices were hardly affected by the exposure to 10 microM Al in an Al-resistant cultivar, Atlas 66. However, similar exposure rapidly inhibited root elongation in an Al-sensitive cultivar, Scout 66 and this was associated with a time-dependent accumulation of Al in the root tissues with more than 77% residing in the cell wall. Al caused a significant decrease in both the viscous and elastic extensibility of cell wall of the root apices of Scout 66. The "break load" of the root apex of Scout 66 was also decreased by Al. However, neither the viscosity nor elasticity of the cell wall was affected by in vitro Al treatment. Furthermore, pre-treatment of seedlings with Al in conditions where root elongation was slow (i.e. low temperature) did not affect the subsequent elongation of roots in a 0 Al treatment at room temperature. These results suggest that the Al-dependent changes in the cell wall viscosity and elasticity are involved in the inhibition of root growth. Furthermore, for Al to reduce cell wall extensibility it must interact with the cell walls of actively elongating cells.

Buckwheat (Fagopyrum esculentum Moench.) is an Al-accumulating plant, but the internal mechanism(s) of detoxification of Al is not fully understood. We investigated the subcellular localization of Al in the leaves of this plant (cv. Jianxi) by directly isolating protoplasts and vacuoles. Pure protoplasts and vacuoles from the leaves of buckwheat, grown hydroponically in Al solution, were obtained based on light-microscopic observation and the activities of marker enzymes of cytosol and vacuoles. More than 80% of total Al in the leaves was present in the protoplasts, and was identified as an Al-oxalate complex (1:3 ratio) by (27)Al-nuclear magnetic resonance. Oxalate and Al in the protoplasts was localized in the vacuoles. These results suggest that internal detoxification of Al in the buckwheat leaves is achieved by both complexation with oxalate and sequestration into vacuoles.