Characteristics of upward translocation of aluminum in plants

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Abstract
There was generally a positive correlation between the A1 content of plant tops and roots under the various concentrations of A1 in the medium, but the slope of the individual regression lines recognized for each plant species was different, and therefore there existed a species difference fin A1 translocation. No correlations were recognized among A1 translocation, water uptake, and root CEC. Extremely high concentrations of A1 considerably increased the translocation of A1 to tops of every plant species examined. Partial excision treatment of roots increased the translocation of A1 to tops. A large amount of A1 was accumulated in all of the cortical cells of the root tip, but at the root proximal most A1 was located in epidermal or hypodermal cells and in endodermal cells adjacent to each protoxylem. These results suggest that A1 translocation may be regulated mainly by epidermis, hypodermis, or endodermis and may be increased by the destruction of the barrier function of cell membranes in roots. Under moderate concentrations of A1 in the medium A1 translocated most in buckwheat among all plant species examined. In buckwheat, A1 was not translocated to tops until the A1 content of roots increased to a certain value, or until some kind of absorption site in the roots was saturated with Al. Smaller translocation of Al to the tops and the stem exudate of all plant species except buckwheat was found at low temperature, while in buckwheat maximum Al content was found even at the low temperature of 7°C. These results suggest the existence of a specific mechanism for the absorption, accumulation, and translocation of Al in buckwheat.