Iron Solubilization Activity of Mugineic Acid and Secretion of Mugineic Acid Family of Phytosiderophores by Barley and Puccinellia chinampoensis Ohwi under Sodic Conditions

In order to clarify contribution of the mugineic acid family of phytosiderophores (MAs) to the iron (Fe) nutrient utilization for the survival of grasses grown in sodic soils, the secretion of MAs from the roots of Puccinellia chinampoensis Ohwi (P. chinampoensis), one of the sodic tolerant grasses, was investigated compared with barley (Hordeum vulgare L. cv. Minorimugi) as a control plant in Fe-depleted hydroponical cultures. It was clarified that the amount of released MAs of barley which have high MAs secretion ability in their roots, was reduced under sodic conditions. On the other hand, the amount of MAs released by P. chinampoensis was increased under the sodic conditions compared with pH 6.5 conditions. It was also shown that MAs release activity of P. chinampoensis was subjected to lesser repression by Na2CO3/NaHCO3 than that of barley. Subsequently, the activity of MA, one of the MAs, to solubilize Fe3+ from gelled Fe3+ in various ion compositions was examined. The results showed that Fe3+ solubilization activity of MAs was maintained stable in the pH range between 8 and 10 and was much repressed by CO32−/HCO3− under pH 10 condition. Because of the repression of Fe3+ solubilization activity of MA by CO32−/HCO3−, it was considered that higher ability to secrete MAs of P. chinampoensis under sodic conditions will give advantage to the plant for survival in sodic soils. Thus, P. chinampoensis is considered to be adapted to sodic conditions. Extensive examination about the behavior of MAs in the rhizosphere of sodic soils and physiological significance of MAs in the sodic tolerant grasses are required in the future.