Aluminium and calcium transport interactions in intact roots and root plasmalemma vesicles from aluminium-sensitive and tolerant wheat cultivars

Abstract

Recent research from our laboratory indicates that aluminium (Al) and calcium (Ca) transport interactions may play an important role in the mechanisms of Al phytotoxicity. In this study, we investigated the effects of Al on Ca2+ transport in intact roots of winter wheat (Triticum aestivum L.) cultivars (Al-tolerant Atlas 66 and Al-sensitive Scout 66). We used both a vibrating Ca2+-microelectrode technique and 45Ca2+ to monitor Ca2+ influx in intact roots. Root apical Ca2+ uptake was immediately inhibited, when roots were exposed to Al levels that ultimately decreased root growth in Al-sensitive Scout 66. The Al-tolerant cultivar was able to resist this Al inhibition of Ca2+ uptake, and to resist Al inhibition of 45Ca2+ translocation from roots to shoots. We also studied Ca2+ transport in right-side out plasmalemma vesicles isolated from roots of Al-sensitive and tolerant wheat cultivars. Calcium influx into the vesicles was mediated by a voltage-gated Ca2+ channel. Aluminium blocks the Ca2+ channel equally well in the plasmalemma vesicles isolated from Al-sensitive and Al-tolerant wheat roots. The results indicate that the differential response observed in intact roots is not due to differences in Ca2+ channels. The Al-tolerant wheat cultivar may have an ability to reduce Al3+ activity in the rhizosphere, thus reducing the Al-inhibition of Ca2+ influx.