The Ameliorative Role of Manganese on Ferrous Toxicity in Rice Plants

Two indica rice genotypes,Milyang 46 and Zhenshan 97B were used as materials to study the rice growth and their Fe,Mn,Zn,P,K concentrations in plants under combined treatments with varied concentrations of Fe2+and Mn2+.The results showed that the plant height,root length,dry weight of shoots and roots of both rice genotypes were significantly affected by Fe and Mn treatments.With increasing levels of Fe2+,the plant height and root length of Zhenshan 97B and Milyang 46 were significantly reduced,indicating that both rice genotypes severely sufferred from ferrous stress.However,the plant height of both rice genotypes were markedly increased with the increasing Mn concentration(0,0.5 and 25 mg / kg),while the root length was not affected;the Mn level of 100 mg / kg inhibited both rice genotypes' plant height.In the same ferrous treatment,compared with 0.5,25 and 100 mg / kg Mn levels significantly improved the dry weight of the two rice plants(shoots and roots),especially under ferrous stress(50,100,and 200 mg / kg),implying that the growth of rice suffered from iron stress could be alleviated by application of Mn.The present experimental results coud not explain the phenomenon that the dry weight of the two rice shoots and roots was significantly lower at 0.5mg / kg Mn level than that at 0 mg / kg Mn level.The results also showed that Fe2+and Mn2+treatment could significantly affect Fe and Mn concentration in root iron plaque and plants(roots and shoots),as well as the concentration of P、K and Zn.Under the same level of ferrous stress(50,100mg / Kg),iron concentration decreased in iron plaque,while increased in roots and shoots with varied Mn levels.Under 200 mg / kg iron treatment,the concentration of Fe in iron plaque and plants decreased with the increasing Mn concentration(0.5,25,100 mg / kg),which likely indicates a direct mechanism by which Mn could alleviate ferrous toxicity in rice plants.The concentration of Mn in iron plaque and plant remarkably reduced with varied Fe2+levels,while significantly increased with varied Mn levels.The increased manganese concentration in solution significantly improved ferrous-stress-induced Mn deficiency.Mn could alleviate ferrous stress.