Alleviation of manganese phytotoxicity in barley with calcium

In order to clarify the mechanism by which calcium (Ca) alleviates manganese (Mn) phytotoxicity, barley plants were grown under the following conditions: (1) nutrient solution alone (control), (2) nutrient solution + 25 mu M Mn (Mn-toxic), and (3) nutrient solution + 25 mu M Mn + 20 mM Ca (Ca-alleviated). Feeding experiments using Mn-54 and Fe-59 (iron) with 2.0 or 20 mM Ca to the plant roots were also conducted. The absorption and translocation of Mn-54 in the control plants were lowered by the high-Ca (20 mM) feeding condition. The translocation of Mn-54 to shoots of Mn-toxic or Ca-alleviated plants was also lowered by the high-Ca feeding condition, but Mn-54 absorption by roots of the plants was unaffected. The absorption and translocation of Fe-59 in the plants was unaffected by the high-Ca feeding condition. Calcium alleviation of Mn phytotoxicity in barley may be induced mainly by the inhibition of Mn translocation to shoots.