Aluminium toxicity in rye (Secale cereale): Root growth and dynamics of cytoplasmic Ca2+ in intact root tips

Abstract

Aluminium (Al.) toxicity in rye (Secale cereale L.), an Al-resistant crop, was examined by measuring root elongation and cytoplasmic free activity of calcium ([Ca2+]cyt) in intact root apical cells. Measurement of [Ca2+]cyt was achieved by loading a Ca2+-sensitive fluorescent probe, Fluo-3/AM ester, into root apical cells followed by detection of intracellular fluorescence using a confocal laser scanning microscope. After 20 min of exposure to 50 μM Al (pH 4.2) a slight increase in [Ca2+]cyt of root apical cells was observed, while the response of [Ca2+]cyt to 100 μM Al (pH 4.2) was faster and larger ([Ca2+]cyt increased by 46% in 10 min). Increases in [Ca2+]cyt were correlated with inhibition of root growth, generally measurable after 2 h. Addition of 400 μM malic acid (pH 4.2) largely ameliorated the effect of 100 μM Al on [Ca2+]cyt in root apical cells and protected root growth from Al toxicity. These results suggest that an increase in [Ca2+]cyt in root apical cells in rye is an early effect of Al toxicity and is followed by the secondary effect on root elongation. © 2002 Annals of Botany Company.