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Characterization of the Inhibition of K⁺ Absorption in Oat Roots by Salicylic Acid ¹

Department of Agronomy, University of Wisconsin, Madison, Wisconsin 53706

The phenolic compounds salicylic acid (o-hydroxybenzoic acid) and ferulic acid (4-hydroxy-3-methoxycinnamic acid) inhibited K⁺ (⁸⁶Rb⁺) absorption in excised oat (Avena sativa L. cv. Goodfield) root tissue. Salicylic acid was the most inhibitory. The degree of inhibition was both concentration- and pH-dependent. With decreasing pH, the inhibitory effect of the phenolic increased. During the early stages of incubation, the time required to inhibit K⁺ absorption was also pH- and concentration-dependent. At pH 4.0, 5x10^–4 molar salicylic acid inhibited K⁺ absorption about 60% within 1 minute; whereas, at pH 6.5, this concentration affected absorption only after 10 to 15 minutes. However, at 5 x 10^–3 molar and pH 6.5, salicylic acid was inhibitory within 1 minute. The capacity of the tissue to recover following a 1-hour treatment in 5 x 10^–4 molar salicylic acid ranged from no recovery at pH 4.5 to complete recovery at pH 7.5. The absorption of salicylic acid was pH-dependent, also. As pH decreased, more of the phenolic compound was absorbed by the tissue. The increased absorption of the compound at low pH most likely contributed to apparent tissue damage at pH 4.5 and might have accounted for the lack of recovery of K⁺ absorption as pH decreased.

Under the proper conditions of pH and concentration, phenolic acids such as salicylic acid could significantly affect mineral absorption by plants in the field.