OBITUARIES

Shang Fa Yang

Shang Fa Yang

Shang Fa Yang, emeritus professor at the University of California, Davis, passed away from complications of pneumonia on February 12, 2007, at the age of 74. His death was sudden and unexpected, leaving his friends and colleagues mourning the loss of an outstanding scientist and mentor. As the discoverer of the pathway for the biosynthesis of ethylene and the namesake of the Yang Cycle for the regeneration of methionine, which initiates this pathway, he leaves a legacy of notable contributions to plant biology.

Shang Fa Yang was born in 1932 in Taiwan, where he received his BS and MS degrees in agricultural chemistry from the National University in the late 1950s. He received a scholarship to do graduate work at Utah State University and received his PhD in plant biochemistry there in 1962. He then went to the University of California, Davis, where he did postdoctoral work with Dr. Paul K. Stumpf on lipid metabolism in higher plants. (In an unfortunate coincidence, Professor Stumpf passed away two days before Shang Fa died.) Shang Fa was eager to see the East Coast and obtained a fellowship to the New York University (NYU) Medical School, where he worked with Professor B. N. LaDu. He returned to California and to plant biochemistry the next year as a postdoctoral scientist with Andrew A. Benson at Scripps Institute of Oceanography in La Jolla, Calif. His stay on the East Coast was rewarding personally, because that is where he met his wife, Eleanor, who was studying accounting at NYU.

In 1966, Shang Fa was hired as an assistant biochemist in the Department of Vegetable Crops at the University of California, Davis. A strong advocate for his hiring was Harlan K. Pratt, a pioneering researcher in ethylene physiology with whom he initially shared a lab in the newly constructed Mann Laboratory. Shang Fa’s early studies on ethylene were assisted by the homemade gas chromatograph that Pratt had cobbled together. Although large and cumbersome, that instrument could measure the parts-per-million concentrations of ethylene produced by plants and remained in use for over 35 years. Armed with this tool and his broad knowledge of chemistry and biochemistry, Shang Fa set out to explore plant ethylene biology.

Since 1934, when ethylene was conclusively shown to be produced by ripening fruit, considerable effort had been expended to discover its biosynthetic pathway in plants. The modern search for the metabolic pathway began in 1965, when Lieberman and Mapson observed that methionine was converted to ethylene in an in vitro model system. Within a year, the same research group confirmed the biological production of ethylene from methionine. This discovery led many scientists around the world on a quest to identify the subsequent steps in the pathway. Shang Fa’s first paper on ethylene in 1966 (one of more than 200 publications in his career) explored the intricacies of the in vitro model system for the generation of ethylene from methionine, and his group made many important contributions during this period.

In 1977, Shang Fa and his PhD student Douglas Adams showed that methionine was converted to S-adenosylmethionine (SAM) and that SAM was a precursor of ethylene. Doug Adams also discovered that when tissues were kept under low oxygen conditions, a treatment known to suppress ethylene biosynthesis and thereby promote postharvest storage of fruits and vegetables, a metabolic intermediate accumulated. The pace quickened, and a real race ensued among various labs, particularly that of Hans Kende at Michigan State University, to identify the intermediate between SAM and ethylene. This intensive effort culminated in 1979 when Adams and Yang identified 1-aminocyclopropane-1-carboxylic acid (ACC) as the final precursor of ethylene. Surprisingly, ACC had been known for a number of years as a nonprotein amino acid of unknown function and was available in crystalline form from a number of chemical supply houses. Following Adams and Yang’s identification of ACC as the ethylene precursor, interest in the compound reached such an intensity that Sigma Chemical had to ration it for a time.

Both the Yang and Kende laboratories quickly developed assays for ACC by chemically converting it to ethylene, and physiological studies into the regulation of ethylene biosynthesis accelerated. Shang Fa’s group demonstrated that under low oxygen conditions, such as root flooding, ACC could accumulate and be transported in the xylem to the shoot and subsequently converted to ethylene, inducing the leaf epinasty characteristic of waterlogged plants. His group discovered that ACC could be conjugated to malonate, resulting in an alternative pool of ACC in plant tissues. He also explored the use of various inhibitors, such as aminoethoxyvinylglycine and cobalt ion, to block the ethylene synthesis pathway at specific steps. It had been noted that methionine pools are too low in plant tissue to sustain the observed rates of ethylene synthesis. Shang Fa and his students demonstrated that the methylthio group released from SAM during the synthesis of ACC is recycled to replenish methionine levels. The reactions of this recycling pathway were subsequently christened the Yang Cycle in plant biochemistry texts.

Another contribution of his group was to demonstrate that plant tissues preferentially converted one of four ethyl-substituted isomers of ACC to butene. As plant extracts contained biologically irrelevant enzyme systems that could generate ethylene from ACC, this observation provided an important criterion that was used in the isolation of the biologically relevant enzyme. As the tools became available to clone and characterize the genes responsible for the steps in ethylene biosynthesis, Shang Fa contributed to many studies of the regulation of those genes in fruit ripening, plant growth, and wounding and stress responses. He wrote numerous reviews and book chapters on ethylene biosynthesis and its role in plant biology that defined this topic for a generation of plant biology students and researchers.

In parallel with these fundamental discoveries related to ethylene, Shang Fa also maintained ongoing and active research programs on auxin metabolism and action, on the biological effects of sulfite and sulfur dioxide, and on cyanide generation and metabolism in plants. In all his work, Shang Fa continually linked his discoveries to practical applications in postharvest biology and plant growth regulation. He used what he knew about physiology to learn more about ethylene biosynthesis, and he applied what he learned about ethylene biosynthesis to contribute to improvements in postharvest storage conditions. He was known for the clarity of his thought and his ability to identify and design critical experimental tests of hypotheses. Shang Fa always maintained an open mind and was willing to challenge accepted ideas, even his own, when they proved untenable in the face of experimental data.

Shang Fa had an uncommon faith in humanity and urged his students to always expect the best of people. The coupling of an affable nature and a genuine concern for his students and colleagues enabled Shang Fa to assemble a powerful and effective research group that shared his vision and strove to match his intensity. He also developed an extensive and international network of friends and colleagues. Despite his many honors, he remained humble and was always willing to share credit for the many discoveries coming out of his lab or to acknowledge the priority of other groups.

Shang Fa figured prominently at many national and international research conferences over the years and served on the editorial boards of leading journals and as a member of several learned societies. He won many awards and honors, including the Campbell Award of the American Institute of Biological Sciences in 1969, a Guggenheim Fellowship in 1982, the International Plant Growth Substances Association Research Award in 1985, and the Outstanding Researcher Award from the American Society of Horticultural Science in 1992. He was named the University of California, Davis, Faculty Research Lecturer in 1992. In 1990 and 1992, he was elected to the National Academy of Sciences, USA, and to the Academia Sinica, Taiwan, respectively. In 1991 he received the prestigious international Wolf Prize in Agriculture.

After taking early retirement from the University of California in 1994, Shang Fa served as professor in the Department of Biology at Hong Kong University of Science and Technology from 1994 to 1997, where he established an active research group, and as a distinguished research fellow and the director of the Institute of Botany at Academia Sinica, Taipei, Taiwan. From 1996 to 1999, he was vice president of the Academia Sinica and directed its numerous research institutes.

Shang Fa is survived by his wife Eleanor and his two sons, Albert and Bryant, who have pursued careers in engineering and chemistry, respectively. His extensive network of friends throughout the worldwide community of scholars and scientists will miss him and regret his early passing. Although future plant biologists will know of Shang Fa through the Yang Cycle and his many other contributions to our field, students and colleagues who were fortunate enough to know him personally will also remember his humor, his humanity, and his sparkling intellect. He will be greatly missed.

Kent J. Bradford and Mikal E. Saltveit
University of California, Davis