Physiological basis of reduced Al tolerance in ditelosomic Lines of Chinese Spring wheat

Aluminum tolerance was assessed in the moderately Al-tolerant wheat (Tritic um aestivum L.) cultivar Chinese Spring and a set of ditelosomic lines deri ved from Chinese Spring. Three ditelosomic lines lacking chromosome arms 4D L, 5AS and 7AS, respectively, exhibited decreased Al tolerance relative to the euploid parent Chinese Spring based on reduced root growth in Al-contai ning solutions. The physiological basis of the reduced Al tolerance was inv estigated. Measurements by inductively coupled argon plasma mass spectrosco py of root apical Al accumulation demonstrated that two of these three line s had a decreased ability to exclude Al from the root apex, the site of Al phytotoxicity. As Al-induced malate exudation has been suggested to be an i mportant physiological mechanism of Al tolerance in wheat, this parameter w as quantified and malate exudation was shown to be smaller in all three del etion lines compared with Chinese Spring. These results suggest that the de creased Al tolerance in at least two of the three ditelosomic lines is due to the loss of different genes independently influencing a single Al-tolera nce mechanism, rather than to the loss of genes encoding alternative Al-tol erance mechanisms.