OBITUARIES

David T. Canvin

David Canvin

David “Dave” Canvin, an eminent plant scientist well known and respected not just in Canada but throughout the world, died on March 16, 2010, at age 78. He was born in 1931 and grew up on a small farm in Selkirk, Manitoba, just north of Winnipeg. After high school, he attended the University of Manitoba in Winnipeg, where he graduated with a BSA in agriculture. He obtained an MSc in plant science, also from Manitoba.

For his PhD, Dave joined Harry Beevers’s research group in the Department of Biology at Purdue University. At that time, Harry was studying the means by which germinating seeds converted storage oil into carbohydrate for the growth of the developing embryo. To determine the pathway involved, Dave fed a variety of 14C-labeled substrates to slices of germinating castor seed endosperm. This pioneering work showed that acetate, produced from the breakdown of fatty acids, was converted to glucose through the operation of the glyoxylate cycle and the reversal of glycolysis. This work, which was published in 1961 in the Journal of Biological Chemistry (1), showed the power of radioisotopes in understanding metabolic pathways and established Dave as an expert in this area. The significance of this early work was demonstrated by the paper’s selection as a Classic by the Journal of Biological Chemistry in 2005 to commemorate 100 years of the JBC.

On completion of his PhD, Dave returned to the University of Manitoba as a professor. However, his tenure there was short because he accepted a position as professor of biology at Queen’s University in Kingston, Ontario, in 1965, where he was to spend the rest of his career.

At Queen’s, he immediately established a research group. However, this time it was not on the breakdown, but rather on the synthesis, of fatty acids in developing castor seeds. The descendents of the original castor plants that Dave established at Queen’s in 1965 are still grown in the greenhouse there and are currently used by plant biochemists such as Bill Plaxton.

Working with graduate students Hugh Drennan and Brian Zilkey, Dave developed a sucrose density gradient procedure for separating the cellular components from castor endosperm and showed that fatty acid synthesis occurred in plastids, not in the soluble phase of the cell as in animals (2). This finding led to considerable controversy but was finally resolved by the demonstration by Ohlrogge and Stumpf that acyl carrier protein, the essential component in fatty acid synthesis, was predominantly in the plastid fraction of plant cells. This again stressed the uniqueness of plant metabolism and the essential role of plastids. It has now been shown that most biosynthetic pathways occur in plastids, an organelle unique to plants.

A number of lively debates between Dave and one of us (D.T.D.) regarding the origin of the carbon in fatty acid biosynthesis led to a very fruitful collaboration that established the presence of a glycolytic pathway in plant plastids. These pathways were catalyzed by isozymes that were shown to be distinct from their cytosolic counterparts, work that helped to establish the importance of the compartmentation of plant metabolism and demonstrated that plant metabolism is quite different from what is found in animals.

In 1968, upon Gleb Krotkov’s sudden death, Dave took over the supervision of Gleb’s research group, which led him into the areas of photosynthesis and photorespiration. Krotkov had shown that when photosynthesis was terminated by extinguishing the light source, there was a burst of carbon dioxide release from the leaves. The amount released depended on the level of oxygen. In an elaborate experiment involving multiple isotopes, Dave showed that carbon was liberated not just on the termination of illumination but during the whole of photosynthesis and that it represented as much as 25% of the carbon that had been newly fixed by photosynthesis. From the measurement of oxygen isotope exchange in leaves, he concluded that photorespiration was an integral part of photosynthesis. It was not until much later that the oxygenase activity of rubisco was found and shown to be responsible for this release of newly fixed carbon. Dave’s pioneering work on gas exchange cemented his reputation as one of the premier experimentalists of his generation.

Dave’s work on photorespiration led in­evitably to him working on organisms such
as green algae and cyanobacteria that appeared to lack the process. He showed that these organisms could concentrate carbon dioxide in their cells, effectively outcompeting oxygen at the active site of rubisco. Through collaboration with a number of students and postdocs, Dave’s team demonstrated that the “CO2 concentrating” mechanism was the product of active CO2 and HCO3- transport. Although the major focus of his work was carbon metabolism, over the years Dave’s lab also produced a range of important discoveries on the processes and location of nitrate and nitrite reduction in plant cells.

When one considers Dave’s research, it is clear that he was at the forefront in establishing new areas of plant metabolism that are now taken for granted. Looking back, we see that his work played a major role in changing the way we envisage plant growth and development. He was a technical expert who was unrelenting in his demand for accuracy. This was illustrated by his advanced undergraduate course on the use of isotopes. This course was viewed as the most technically demanding undergraduate laboratory course in the department, and it trained a generation of exceptionally talented biochemists. The first experiment consisted of each student being given a black bottle in which Dave had placed a carefully measured amount of water. The students were supplied with a radioactive solution. All they had to do was pipette some of this solution into the bottle, measure the reduction in radioactivity, and hence deduce the volume of water, but the work had to be very accurate and students could not proceed with the next experiment until they got it right. As the course progressed, students carried out experiments measuring ¹⁴CO₂ gas exchange and tracing ¹⁴C-labeled substrates as they were metabolized through a variety of pathways.

Dave’s impact, however, goes beyond a simple discussion of his research accomplishments. He was a great mentor not just to his students and postdocs, but to his university colleagues and just about anyone who knew him. He would give endlessly of his time and expertise to help anyone willing to work hard and strive for excellence. He did not suffer fools gladly. He would challenge every scientific conclusion from a wide range of fields and expected the proponent to defend his or her position in discussions that could last for hours, days, or years. His integrity and honesty were absolute.

Outside of research, he made many contributions at Queen’s University, within Canada, and internationally. He served on the Queen’s Senate, was president of the Faculty Association, the head of the Biology Department, and dean of Graduate Studies. In all these areas, he made very significant contributions to the university.

Nationally, he served and was chair of the NSERC Plant Biology Grants Committee, a member of the Ontario Graduate Programme Appraisal Committee, a member of the Technical Advisory Committee on Nuclear Fuel Waste Management, chair of the Committee of Heads of Biology in Ontario, secretary–treasurer of the Biological Council of Canada, and director of the Botanical Association.

Dave’s leadership in research was also matched by his service to the Canadian Society of Plant Physiologists (CSPP), including his tenure as CSPP’s secretary–treasurer, vice president, and president. In 1981, he was awarded the CSPP Gold Medal for outstanding published contributions and distinguished service to plant physiology in Canada.

Internationally, he served on the editorial board of Plant Physiology; Planta; Plant, Cell & Environment; Photosynthesis Research; and the Canadian Journal of Biochemistry. He was twice a consultant to the Food and Agriculture Organization (FAO) of the United Nations and twice a consultant to the FAO/International Atomic Energy Agency. In 1977, he was elected a fellow of the Royal Society of Canada.

Perhaps as a reversion to his early life on the farm, Dave retired from Queen’s in 1995 to fulfill a revelation that had occurred to him while in the hospital for a bypass operation on his leg. Much to everyone’s surprise, he bought and operated Snug Harbour, a resort situated on beautiful Desert Lake about 35 miles north of Kingston. There he could be found mending cottage roofs, renting boats, or simply drinking a beer with cottagers or visitors.

Dave is survived by his wife of 52 years, Marie, and three sons, Steven, Paul, and Robert. His daughter, Sarah, died in 2006. In all respects, he was a remarkable man who made a major contribution to our understanding of plants, but he was also someone it was a privilege to know and have as a friend.

David T. Dennis
David H. Turpin
David B. Layzell

References

1. Canvin, D.T., and Beevers, H. (1960). Sucrose synthesis from acetate in the germinating castor bean: Kinetics and pathway. Journal of Biological Chemistry 236: 988–995.
2. Canvin, D.T., and Zilkey, B.F. (1972). Localization of oleic acid biosynthesis enzymes in the proplastids of developing castor endosperm. Canadian Journal of Botany 50: 323–326.