Harold Evans

Harold J. Evans

Harold J. Evans passed away on October 20, 2007, in Lake Oswego, Oregon, following several years of declining health initiated by a stroke. He is survived by his wife, Mavis, and two daughters, Heather and Pam. During his long academic career, he set the gold standard for scientific rigor and tenacity in uncovering the secrets of plant physiology, particularly regarding mineral nutrition and the process of nitrogen fixation.

Harold was born in 1921 in Franklin, Kentucky, and attended the University of Kentucky to obtain his BS (1946) and MS (1948) degrees. His doctoral work was conducted at Rutgers University (1950), where he became a pioneer in research on the effects of deficiency of trace elements in plants. Following a brief stint as a postdoc at Johns Hopkins, he soon moved into the faculty ranks in the Botany Department at North Carolina State University, working up to full professor before he left for Oregon State University in 1961. He served in several capacities in Oregon, including professor of plant physiology; affiliate professor of biochemistry; and director of the Laboratory for Nitrogen Fixation Research, an independent department that he created and led to international prominence.

His list of awards and honors is too long to cite fully, but highlights include membership in the National Academy of Science, the Oregon Academy of Science Award, the University of Kentucky Distinguished Alumnus Award, The Johns Hopkins University Society of Scholars Award, ASPB’s Charles Reid Barnes Award, a stint as president of the American Society of Plant Physiologists (1970), and appointment as Oregon State University Distinguished Professor (the highest honor at that institution).

He published about 200 scientific papers concerning the biochemical role of minerals and various aspects of biological nitrogen fixation. His fundamental discoveries include the demonstration of the essential roles of molybdenum and cobalt for nitrogen-fixating legumes, the enzymatic mechanism of nitrate reduction in plants (highly cited work from 1953), the influence of metal activators on enzymes (e.g., pyruvate kinase and malic enzyme), the function of the glyoxylate cycle in legume nodules, the first application of the acetylene reduction technique to nodules, the first purification of active nitrogenase from nodules, the first report of nitrogen fixation by free-living rhizobia, the role of polyhydroxybutyrate (PHB) in nodules, characterization of diverse nitrogen-fixing systems (grasses, rotting wood, marine environments, terrestrial wetlands, maize, and actinorhizal plants), the essential features of the hydrogenase uptake system in rhizobia, the roles of nickel and selenium in nodules, and the importance of antioxidants in nodules. Toward the end of his remarkably productive career, he astounded the world of nitrogen fixation by culturing rhizobia with H₂ and CO₂ as the sole source of energy and carbon, respectively, thus establishing their ability to grow as chemolithotrophs. He also showed that rhizobia’s ability to utilize H₂ via an uptake hydrogenase provides substantial benefits to legumes, because nitrogenase invariably releases H₂ as a byproduct of nitrogen fixation, and this H₂ represents a considerable energy drain. The presence of hydrogenase genes in some rhizobia makes them more efficient as symbionts and thus of considerable practical benefit for agricultural productivity.

Harold had an enviable record of 32 years of continuous funding from NSF, a run that ended only on his retirement in 1988. In addition to his scientific contributions, Harold’s legacy consists of the dozens of professional plant scientists who continue the quest today, having been graduate students and postdocs under his supervision.

David Dalton
Reed College
Dan Arp
Oregon State University