Al-binding capacity of plasma membrane of root-tip portion in relation to Al tolerance

Abstract

Differences in aluminum (Al) sensitivity of cultivars within a species may be related to differences in Al binding by the plasma membrane of root-tip portion. In every plant species tested, i.e., rice (Oryza sativa L.), maize (Zea mays L.), pea (Pisum sativum L.), wheat (Triticum aestivum L.) and sorghum (Sorghum bicolor (L.) Moench), the Al concentration in the 1-cm tip of the root was higher in the Al-sensitive cultivar than in the Al-tolerant one. In contrast, the relative concentrations of P, K or Mg, which entirely or mainly localize in the symplast, in the control and Al treatments were higher in the Al-tolerant cultivar. At pH 5, the cation-exchange capacity (CEC) of the dry root powder from the 1-cm root tip portion of the cultivars were similar, and no correlation was recognized between Al tolerance and root CEC in any of the plant species. The following mechanism is suggested: the plasma membrane of the root-tip portion binds to Al ions, and is impaired thereafter. Eventually, the leakage of larger amounts of К and P and permeation of Al ions are induced in Al-sensitive cultivars.