Assimilation of C14, N15 labeled urea by excised apple & peach leaves

Abstract

C14, N15 labeled urea was infiltrated into apple and peach leaves through the petiole. Amino acids were separated by ion-exchange column and paper chromatography and their isotope content determined. Urea hydrolysis proceeded to a greater extent in peach than in apple leaves, as evidenced by residual urea and comparison of isotope incorporation into leaf constituents. C14 and N15 were readily incorporated into amino acids, amides, and protein within 20 hours. Comparison of amino acid C14/N15 ratios indicate urea assimilation after hydrolysis to C14O2 and N15H3. C14/N15 ratios for amino acids indicate the initial hydrolysis step limits urea assimilation in apple but not peach leaves. All evidence obtained indicated that the failure of peach leaves to effectively utilize foliar-applied urea is not due to their inability to hydrolyze nor subsequently assimilate urea.