Uptake of aluminium into Arabidopsis root cells measured by fluorescent lifetime imaging

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Abstract

Background and Aims

Measuring the Al3+ uptake rate across the plasma membrane of intact root cells is crucial for understanding the mechanisms and time-course of Al toxicity in plants. However, a reliable method with the sufficient spatial and temporal resolution to estimate Al3+ uptake in intact root cells does not exist.

Methods

In the current study, fluorescent lifetime imaging (FLIM) analysis was used to quantify Al3+ uptake in the root-cell cytoplasm in vivo. This was performed via the estimation of the fluorescence lifetime of Al–lumogallion {5-chloro-3[(2,4-dihydroxyphenyl)azo]-2-hydroxybenzenesulfonic acid} complexes and measurements of intracellular pH while exposing arabidopsis seedlings to acidic and Al3+ stresses.

Key Results

The lifetime of Al–lumogallion complexes fluorescence is pH-dependent. The primary sites for Al3+ entry are the meristem and distal elongation zones, while Al3+ uptake via the cortex and epidermis of the mature root zone is limited. The maximum rates of Al uptake into the cytoplasm (2–3 µmol m−3 min−1 for the meristematic root zone and 3–7 µmol m−3 min−1 for the mature zone) were observed after a 30-min exposure to 100 µM AlCl3 (pH 4·2). Intracellular Al concentration increased to 0·4 µM Al within the first 3 h of exposure to 100 µM AlCl3.

Conclusions

FLIM analysis of the fluorescence of Al–lumogallion complexes can be used to reliably quantify Al uptake in the cytoplasm of intact root cells at the initial stages of Al3+ stress.

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