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Role for Potassium in the Iron-Stress Response Mechanism of Iron-Efficient Oat

School of Natural Resources, Univ. of Missouri, Columbia, MO 65211

V. D. Jolley^* and J. C. Brown

Dep. of Agronomy and Horticulture, 275 WIDB, Brigham Young Univ., Provo, UT 84602

* Corresponding author.

ABSTRACT

Adequate soil K enhances the ability of certain Fe-deficiency-stressed monocotyledonous and dicotyledonous plants to obtain Fe. In dicotyledonous plants, this increased capacity to obtain Fe where adequate K is present is associated with specific Fe-stress response mechanisms including H⁺ ion efflux, reductant release, and reduction of Fe³⁺ to Fe²⁺ at the root (Strategy I). A different Fe-stress response mechanism recently identified in Fe-efficient grasses is the release of phytosiderophore (a plant-produced Fe³⁺ chelator; Strategy II). Our objective was to determine if varied K additions affect either the production and release of phytosiderophores or the uptake of Fe in oat (Avena sativa L.; a Strategy II plant). A series of hydroponic experiments was conducted imposing varying solution K concentrations on Fe-deficiency-stressed ‘Coker 227’ oat, an Fe-efficient cultivar. Significantly more phytosiderophore was released by roots of oat plants grown with adequate K (84 mg K L^–1) than by roots of plants grown at low concentrations of solution K (0 and 7 mg K L^–1). The diminished phytosiderophore production in the absence of K corresponded significantly with greater Fe-deficiency chlorosis and lower leaf Fe contents. Oat plants grown in adequate K successfully competed with equimolar concentrations of Fe and EDDHA [ethylene-diamine di (O-hydroxyphenylacetic acid)], but did not compete for Fe where excess EDDHA was added, further substantiation of a role for K in the production and release of phytosiderophore.

Received for publication May 20, 1991.