Mechanism of potassium alleviation of manganese phytotoxicity in barley

Manganese (Mn) toxicity and potassium (K) deficiency are the major factors that limit plant growth and development in acid soils. The objective of this study was to assess the role of high K on the alleviation of Mn toxicity in barley (Hordeum vulgare L. cv. 'Minorimugi') grown in a phytotron for 14 d. Modified half-strength Hoagland-Arnon solution (pH 5.5) was used as the medium. The treatments were (1) 0.25 mu M Mn + 3 mM K (control); (2) 25 mu M Mn + 3 mM K (Mn-toxic); and (3) 25 mu M Mn + 30 mM K (K-alleviated). The Mn-toxic plants showed the symptoms of Mn toxicity and mild iron (Fe) deficiency, whereas in the K-alleviated plants such symptoms were absent. The K-alleviated plants had dry weight, chlorophyll content, and Fe concentration similar to that in the control plants, indicating that high K (30 mM) in the growth medium could alleviate Mn toxicity and Mn-induced Fe deficiency. Roots of plants fed separately with Mn-54 and Fe-59 in the presence of 3.0 and 30 mM K for 4 h were also studied. Results showed that high K could help in avoiding the accumulation of Mn-54, indicating that K plays an antagonistic role on Mn absorption by roots of barley and its subsequent translocation to the shoots. However, the absorption of Fe-59 was not influenced by the high K concentration in a short-term experiment (4 h), indicating that high K does not affect short-term Fe absorption by the roots of barley plants. These results suggested that the alleviating effect of high K could be attributed to the antagonistic effect of K on Mn absorption by roots and translocation into shoots.