ALUMINUM EFFECTS ON CALCIUM-UPTAKE AND TRANSLOCATION IN WHEAT FORAGES

The effects of Al on Ca transport could influence Ca accumulation in plants. Low forage C2 concentrations may cause hypocalcemia, a Ca deficiency syndrome of ruminants. Solution culture experiments were conducted in a growth chamber to examine the effects of Al (5-50 muM) on uptake and translocation of Ca (Ca-45) in winter wheat (Triticum aestivum L.) cultivars (Al-tolerant Atlas 66 and Al-sensitive Scout 66). Three-day-old seedlings, grown either in a CaCl2 solution (0.1 or 1.0 mM) or in a complete-nutrient solution, were used. For plants grown in CaCl2 solution, addition of 5 muM Al significantly decreased Ca uptake and translocation in Scout 66, but not in Atlas 66. Higher levels of Al (20 and 50 muM) decreased Ca uptake and translocation much more in Scout 66 than in Atlas 66. For plants grown in complete-nutrient solution, Al (5-50 muM) exposure for up to 6 h had little effect on Ca uptake and translocation in either cultivar. This may be due to the reduction in Al3+ activities in the external solution, as well as lowered Al3+ activities near the root-cell plasmalemma. When roots were exposed to Al for 24 h, Ca uptake and translocation were decreased significantly in Scout 66, but were little affected in Atlas 66. The percentage of Ca translocated to the shoots was significantly decreased by Al in Scout 66, but not in Atlas 66. These results suggest that Al inhibits both Ca uptake and translocation in Scout 66, but inhibits primarily root Ca uptake in Atlas 66 (and only at higher Al levels). It appears that the use of Al-tolerant cultivars of wheat forages on acid soils could be important for maintaining proper Ca nutrition of grazing animals.