14 Nickel Nickel (Ni), the most recently discovered essential element (1), is unique among plant nutrients in that its metabolic function was determined well before it was determined that its deficiency could disrupt plant growth. | 6 30 2006 3 31 PM Page 395 14 Nickel Patrick H. Brown University of California Davis California CONTENTS Introduction .395 Discovery of the Essentiality of Nickel .396 Physical and Chemical Properties of Nickel and Its Role in Animal and Bacterial Nickel-Containing Enzymes and Proteins .397 Essentiality and Function of Nickel in Plants .398 Influence of Nickel on Crop Growth .400 Diagnosis of Nickel Symptoms of Deficiency and Concentration of Nickel in Plants .403 Uptake and Nickel in Soils .404 Nickel Concentration in Soils .404 Nickel Analysis in Soils .405 Nickel Fertilizers .405 Conclusion .406 References .406 INTRODUCTION Nickel Ni the most recently discovered essential element 1 is unique among plant nutrients in that its metabolic function was determined well before it was determined that its deficiency could disrupt plant growth. Subsequent to the discovery of its essentiality in the laboratory Ni deficiency has now been observed in field situations in several perennial species 2 . The interest of plant scientists in the role of nickel was initiated following the discovery in 1975 3 that it was a critical constituent of the plant enzyme urease. The ultimate determination that nickel was essential for plant growth 1 depended heavily on the development of new techniques to purify growth media and to measure extremely low concentrations of nickel in plants. The establishment of nickel as an essential element however highlights the limitations of the current definition of essentiality of nutrients as applied to plants 4 . It has been argued for example that even though nickel is clearly a normal and functional constituent of plants it does not fulfill the definition of essentiality since urease is not essential for plant growth and nickel deficiency apparently does not prevent the completion of the .
