Mechanism of potassium alleviation of manganese phytotoxicity in barley evaluated by short-term absorption of manganese-54 and iron-59

The mechanism of K alleviation of Mn toxicity and Mn-induced Fe deficiency was studied in barley (Hordeum vulgare L. cv.Minorimugi).Plants were grown hydroponically under normal (0.25 IJ-M Mn and 3.0 mM K), Mn-toxic (25 J-I-M Mn and 3.0 mM K), and K-alleviated (25 jJ.M Mn and 30 mM K) conditions in a phytotron.Plants grown under different conditions were transferred to a nutrient solution (1/2-strength Hoagland-Arnon solution) and fed separately with 54Mn or 59Fe (37 kBq of each) in the presence of two levels of K (3.0 or 30 mM) for 4 h.The amount of Mn absorbed for 4 h in the shoots and the roots of all the plants transferred to a high K level (30 mM) was lower than that of the plants transferred to a low K level (3.0 mM).The alteration in the amount of absorbed Mn in the shoots and the roots of the plants may reveal an antagonistic effect of K on Mn absorption.On the other hand, a high K level did not affect the amount of Fe absorbed for 4 h in the shoots and the roots of the normal plants and plants with Mn toxicity (hereafter referred to as "Mn-toxic plants"), while a low K level increased the amount of absorbed Fe in the shoots and the roots of the K-alleviated plants.However, a high K level increased the amount of adsorbed Fe for 4 h in the root apoplast of the Mn-toxic plants.The results of our shortterm experiments suggested that the decreasing effect of a high K level on Mn absorption could playa significant role in the alleviation of Mn phytotoxicity and that the alleviation effect of a high K level might not be related directly to Fe absorption in plants.