Submitted to: Journal of the American Society for Horticultural Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/28/2007
Publication Date: 5/10/2007
Citation: Bai, C., Reilly, C.C., Wood, B.W. 2007. Nickel deficiency affects nitrogenous forms and urease activity in spring xylem sap of pecan. Journal of the American Society for Horticultural Science. 132:302-309. Interpretive Summary: Little is known regarding the role of nickel in plant nutrition and how nitrogen management practices in agricultural operations are influenced by nickel. The influence of nickel deficiency on nitrogen metabolism was studied. It was found that nickel deficiency disrupts metabolism of nitrogenous substances. This work implicates nickel as potentially limiting the efficacy of nitrogen management strategies in agricultural crops.
Technical Abstract: While nickel (Ni) deficiency occurs in certain agricultural crops, little is known regarding the influence of deficiency on metabolic or physiological processes. We studied the influence of Ni deficiency on the reduced-nitrogen (N) composition of early spring xylem sap of pecan [Carya illinoinensis (Wangenh.) K. Koch]. HPLC analysis of sap composition found that the presence of ureido-, amide- and amino-N substances and that they are quantitatively influenced by tree Ni nutritional status. Ureido-N forms quantitatively dominated amide-N forms in regards to both molar concentration and the forms in which reduced N-atoms are present; thus pecan appears to be predominately a ureide transporting species. The primary ureido-N substances in sap of Ni-sufficient (Ni-S) trees are citrulline ' asparagine ' xanthine > ureidoglycolate > allantoic acid > allantoin ' uric acid ' urea. Asparagine is the primary amide-N form, while there are only traces of amino-N forms (e.g., tryptamine and '-phenylethylamine) in xylem sap. Nickel deficiency substantially increased of citrulline and allantoic acid in xylem sap while decreasing asparagine, xanthine, and '-phenylethylamine concentrations. These Ni linked quantitative shifts in reduced-N forms indicate that Ni nutrition potentially affects intermediates of both the ureide catabolic pathway and the Urea Cycle, and the N:C economy of the tree. Xylem sap associated urease specific activity was also reduced as a consequence of Ni deficiency. These results indicate that Ni deficiency potentially disrupts normal N-cycling via disruption of ureide metabolism.