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Metabolism and Enzymology

Induction of Barley Leaf Urease ¹

Crop Science Department, Oregon State University, Corvallis, Oregon 97331-3002

Foliar urea application on barley plants increased leaf urease activity for 5 hours with a peak of 20-fold at 2 hours. To discern the mode of urease induction, urea with or without inhibitors and [³⁵S]methionine were incubated with leaf sections for different lengths of time. Urease was extracted, partially purified, electrophoresed, and then quantified by fluorogram. Five urease (U) isozymes were separated by PAGE. U_a and U_b might be polymers or complexes that occurred only at the peak of induced activity. U₁ and U₂ appeared at 0.5 and 0.75 hour, respectively, after urea induction, peaked at 2 hours, and persisted only in treated leaves for several additional hours indicating that they are transient inducible forms. U₃ was the constitutive form present in control and treated leaves. Induction with cordycepin or cycloheximide completely prevented urea stimulated activity and nullified the existence of isozymes U_a, U_b, U₁, and U₂. ³⁵S-U₁, which was labeled in the last hour of induction, appeared on fluorogram 1 hour after induction, peaked at 2 hours, and declined at 3 hours. Results indicated that de novo synthesis of urease is activated by the influx of urea.

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