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Environmental and Stress Physiology

Accumulation of Apoplastic Iron in Plant Roots ¹

A Factor in the Resistance of Soybeans to Iron-Deficiency Induced Chlorosis?

Agronomy Department, Cornell University, Ithaca, New York 14853, U.S. Department of Agriculture-Agricultural Research Service, Ithaca, New York 14853, Plant, Soil and Nutrition Laboratory, Ithaca, New York 14853

We hypothesized that the resistance of Hawkeye (HA) soybean (Glycine max L.) to iron-deficiency induced chlorosis (IDC) is correlated to an ability to accumulate a large pool of extracellular-root iron which can be mobilized to shoots as the plants become iron deficient. Iron in the root apoplast was assayed after efflux from the roots of intact plants in nutrient solution treated with sodium dithionite added under anaerobic conditions. Young seedlings of HA soybean accumulated a significantly larger amount of extracellular iron in their roots than did either IDC-susceptible PI-54619 (PI) soybean or IDC-resistant IS-8001 (IS) sunflower (Helianthus annus L.). Concurrently, HA soybean had much higher concentrations of iron in their shoots than either PI soybean or IS sunflower. The concentration of iron in the root apoplast and in shoots of HA soybean decreased sharply within days after the first measurements of extracellular root iron were made, in both +Fe and –Fe treatments. The accumulation of short-term iron reserves in the root apoplast and translocation of iron in large quantities to the shoot may be important characteristics of IDC resistance in soybeans.

¹ Contribution from the U.S. Department of Agriculture in cooperation with the Department of Agronomy, Cornell University, Paper No. 1681.

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