Poster: Membrane Transport

Abs # 1217: Ion flux kinetics from ES8 and ET8 wheat roots: pinpointing the underlying mechanisms of Al³⁺ tolerance

Presenter:	Shabala, Sergey , Sergey.Shabala@utas.edu.au
Authors	Shabala, Sergey  (A)   Wherrett, Tim  (A)   Ryan, Peter  (B)
Affiliations:	(A): School of Agricultural Science, University of Tasmania, Hobart, Australia (B): CSIRO Plant Industry, Canberra, Australia

Aluminium toxicity severely limits plant growth in acidic soils, causing rapid cessation of root growth. In wheat, mechanisms of Al³⁺ tolerance are associated with release of malate. ET8 and ES8 are near isogenic lines that differ in Al³⁺ tolerance at a single dominant locus. Sensitivity to Al³⁺ and release of malate is restricted to the root tip. It has been hypothesised that sustained release of malate requires an equivalent efflux of K⁺as charge balance. In this study, this hypothesis was tested by measuring Al³⁺-induced fluxes of Cl^-, H⁺ and K⁺ fluxes from meristem, elongation and mature regions of ET8 and ES8 cultivars immediately and 24 h after addition of Al³⁺, using the MIFE technique. 50µM Al³⁺ stimulated an immediate transient increase in K⁺ efflux from ET8 plants, most likely associated with charge balance of malate efflux. In contrast K⁺ efflux was immediately reduced in ES8. K⁺ fluxes after 24 h exposure to Al³⁺ were also consistent with these observations. The difference between cultivars was apparent in the elongation region only. This is the first real time evidence of Al³⁺ stimulated K⁺ efflux kinetics in tolerant but not sensitive wheat varieties. Occurrence of efflux only in the elongation zone also suggests that malate efflux in wheat is restricted to this region. Previously the best spatial resolution of malate release was the root tip. Our data also revealed a crucial role of Cl^- as a major osmoticum required for extension growth. Cl^- influx was maintained in ET8 but not ES8 at Al³⁺ concentrations where root extension still occurs 24 h after addition. It appears that in intact roots the anion channel is selective for malate^2- over Cl^-. Maintenance of Cl^- influx may also contribute to membrane charge balance associated with malate extrusion.