Aluminium interactions with K+(86Rb+) and 45Ca2+ fluxes in three cultivars of sugar beet (Beta vulgaris)

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Abstract
Three cultivars of sugar beet (Beta vulgaris L.), which are sensitive to aluminium (Al) in the order Primahill > Monohill > Regina, were grown in water culture for 2 weeks. Nutrients were supplied at 15% increase of amounts daily, corresponding to the nutrient demand for maximal growth. The 2.4‐dinitrophenol (DNP)‐sensitive (metabolic) and DNP‐insensitive (non‐metabolic) uptake of aluminium, phosphate. 45Ca2+ and K+(86Rb+) in roots were measured as well as transport to shoots of intact plants. All 3 cultivars absorbed more aluminium if DNP was present during the aluminium treatment than in its absence. It is suggested that sugar beets are able to extrude aluminium activity or that they possess an active mechanism to keep Al outside the cell.The presence of Al in the medium during the 1‐h experiment affected the metabolic and non‐metabolic fluxes of 45Ca2+ and K+(86Rb+) in different ways. In the presence of DNP, the influx of both 45Ca2+ and K+(86Rb+) and the efflux of 45Ca2+ were inhibited by Al in a competitive way. At inhibition of 45Ca2+ influx, 2 Al ions are probably bound per Ca2+ uptake site in cv. Regina (Al‐tolerant), but in cvs Primahill and Monohill only one Al ion is bound (more Al sensitive). Aluminium competitively inhibited the active efflux of 45Ca2+ (absence of DNP) in almost the same way in the 3 cultivars. In contrast, aluminium stimulated the influx of K+(86Rb+) in cvs Primahill, Monohill and Regina in the absence of DNP. Thus, the Al effects on active and passive K+(86Rb+) influx are different. The total influx of K+(86Rb+) increased in the presence of Al and might be connected to an active exclusion of Al. Regina is the least Al‐sensitive cultivar, probably because Al interferes less with the Ca2+ fluxes and because this cultivar actively excludes phosphate in the presence of Al. Thus Al‐phosphate precipitation within the plant could be avoided.