Effects of aluminum stress on wheat root tip cytoplasmic proteins and malate efflux

In the present study, a pair of near iso-genic wheat line, ET8 and ES8, was used to investigate the effects of aluminum (Al) stress on root growth, root tip Al content, root tip cytoplasmic protein, and malate efflux from their roots. Root elongation was decreased with increasing Al concentrations applied, but it was always higher in ET8 than in ES8, indicating high Al tolerance in ET8. Total Al content in root tips was significantly lower in ET8 than in ES8 suggesting the role of Al exclusion mechanism in Al tolerance of ET8. After 50 mol/L Al exposure for 24 h, SDS-PAGE cytoplasmic protein profiles in root tips were severely affected in ES8 but not in ET8. Furthermore, Al-induced malate efflux was significantly higher in ET8 than in ES8, indicating that exclusion of Al from root tips is due to efflux of malate from wheat roots. Although ET8 was higher in Al tolerance than ES8, the root growth was still inhibited by 50 mol/L Al exposure for 24 h. We hypothesise that Al may inhibit root elongation apoplastically rather than cytoplasitically.