Aluminium induces an increase in cytoplasmic calcium in intact wheat root apical cells

Abstract

Disturbance of cytoplasmic Ca ²⁺ homeostasis, leading to breakdown in Ca ²⁺ -mediated signal transduction processes, has been suggested as a primary mechanism of aluminium (Al) rhizotoxicity in plants. To test this hypothesis, Al-related changes in cytoplasmic free activity of Ca ²⁺ ions ([Ca ²⁺ ] _c ) in root apical cells of near-isogenic wheat (Triticum aestivum L.) lines differing in Al tolerance at a single locus were examined by visualising the Ca ²⁺ -sensitive probe Fluo-3 with confocal laser scanning microscopy. Exposure of roots to 50 µM AlCl ₃ (pH 4.2) led to an increase in [Ca ²⁺ ] _c of root apical cells in both Al-sensitive (ES8) and Al-tolerant (ET8) wheat lines. An increase in [Ca ²⁺ ] _c was greater in ES8 than in ET8; after 1-h treatment with 50 µM AlCl ₃ an increase in [Ca ²⁺ ] _c was 48 and 27 % in ET8 and ES8, respectively. An increase in [Ca ²⁺ ] _c of ES8 roots, but not ET8 roots, was observed upon treatment with 2.6 µM AlCl ₃ (pH 4.5). Al-related increases in [Ca ²⁺ ] _c were correlated with inhibition of root growth. The Al-induced increase in the [Ca ²⁺ ] _c was reversible upon removing AlCl ₃ . These findings provide direct evidence to support the hypothesis that Al interactions with cytoplasmic Ca ²⁺ are involved in the Al toxicity syndrome in plants.