DIFFERENTIAL CULTIVAR RESPONSE TO POLYNUCLEAR HYDROXO-ALUMINUM COMPLEXES

Recent evidence has indicated that polynuclear hydroxo-Al complexes may be more toxic to certain plant species in solution culture than the hexaaqua or other mononuclear Al complexes. The objective of this study was to investigate the response of six wheat (Triticum aestivum L.) cultivars, having a demonstrated differential tolerance to Al under field conditions, to mononuclear and polynuclear Al when exposed in a solution culture bioassay system. The order of cultivar tolerance to mononuclear Al observed in this investigation was 'Yecora Rojo'> 'Titan'> 'Caldwell'> 'Wampum'> 'Hart,' which is identical to that reported for these cultivars grown in acid soils. This observation demonstrates the utility of the hydroponic bioassay technique as a simple and effective means for screening genetically diverse plants for Al tolerance. Consistent with some previous reports, polynuclear Al was found to be much more toxic to all of the wheat cultivars studied than mononuclear Al, yet, in contrast to the limited data on polynuclear Al toxicity to wheat cultivars differing in Al tolerance, some differential response among cultivars was noted. The order of cultivar tolerance to polynuclear Al generally agreed with that of mononuclear Al, at least at the highest concentration of polynuclear Al, i.e., 7 muM. Based on the nature of the partially neutralized Al stock solutions utilized, we concluded that the toxic polynuclear Al component is the Al13 species.