Differential impacts of aluminium on microtubule organisation depends on growth phase in suspension-cultured tobacco cells

We investigated the impacts of aluminium (Al) on the structural organisation of microtubules (MTs) in suspension-cultured tobacco (Nicotiana tabacum L. cv. Samsun) cells using monoclonal anti-tubulin antibodies coupled with confocal microscopy. Cells were treated with Al (50 μM) in a simple calcium solution (3 mM CaCl₂ and 3% [w/v] sucrose, pH 4.5) up to 24 h. The impacts of Al on tobacco cells were found to be distinct, depending on the growth phase of cells. Cells at logarithmic (log) phase lost their structural integrity of phragmoplasts and spindle MTs during Al treatments. In log-phase cells, the cortical microtubules (CMTs) showed no visible changes in the initial 1 h, but progressive alteration, such as less prominent (after 6 h) and intensive (from 12 h onwards) depolymerisation of MTs, was registered upon increasing Al treatment duration, which accompanied Al-induced callose formation. The growth of log-phase cells showed a tendency of inhibition between 6 and 12 h Al treatment, which led to significant growth inhibition from 12 h onwards, suggesting that Al-induced depolymerisation of CMTs in log-phase cells is closely linked to the Al-induced inhibition of cell growth. In contrast, Al-induced stabilisation of CMTs was found in stationary-phase cells and these cells required higher Al levels (100 μM) for the depolymerisation of CMTs. These results provide first circumstantial evidence for both depolymerisation and stabilisation of MTs induced by Al, depending on the phases of plant cell growth.