Submitted to: International Journal of Horticultural Science
Publication Type: Proceedings
Publication Acceptance Date: 3/15/2006
Publication Date: 8/13/2006
Citation: Bai, C., Yi, S., Reilly, C.C., Wood, B.W. 2006. Insights into the nutritional physiology of nickel. In: Proceedings of the International Journal of Horticultural Science. 27th International Horticultural Congress, August 13-19, 2006, Soul, Korea, p. 127-128. Interpretive Summary: The role of nickel in plant metabolism and physiology is poorly understood. The discovery of nickel deficiencies in plants has underscored the need to understand the ro;e of in plants. It was found that nickel plays a major role in primary plant metabolism, especially regarding nitrogen usage. A novel form of urease was also found. These discoveries highlight the importance of nickel in plant nutrition and provide insight into other roles of nickel in plants, thus ultimately enabling better plant yields.
Technical Abstract: Abstract: The nutritional physiology of nickel (Ni), an essential nutrient element, is poorly understood. The recent discovery of Ni deficiency in certain horticultural crops evokes multitudes of questions regarding the role of Ni in metabolism, physiology, and culture of crops. We found for pecan (Carya illinoinensis), a woody perennial), that nitrogen (N) metabolism is greatly influenced by plant Ni status via its influence on ureide catabolism, amino acids metabolism, and mobilization of N reserves. Spring xylem sap differs in ureide composition depending upon Ni status, resulting in accumulation of asparagine anhydrous, but reduction of citrulline, allotonic acid, total ureides and urease activity. Of especial significance is that sap also contained a novel 14 kDa protein possessing urease activity. Its N-terminal amino acids (residues 1 - 17) are identical to 13,473 Da bovine pancreatic RNase A (residues 5 - 21) and its chain A residues (1 - 17). Thus the pure protein is designated "RNase A - Urease" (EC 18.104.22.168 - EC 22.214.171.124) and a previously unknown third urease isoform in plants. RNase A - Urease requires Ni ions for activation and appears to assist in the catabolism of stored N forms being translocated in spring xylem sap to growing points. Enzyme assays also revealed that bovine pancreatic RNase A possesses substantial urease catalyzing activity. Because RNase A is also a urease, the discovery implicates a generally ubiquitous role for RNase A in the cycling of N in plant and animal cells and highlights the importance of Ni nutritional status.