Clarence A. "Bud" Ryan

Clarence A. Ryan (1931 – 2007), often known as Bud Ryan, was an American plant biochemist whose research revealed key molecular mechanisms underlying plant defense responses to herbivory. He spent most of his career at Washington State University, where his laboratory discovered the peptide signaling molecule systemin, the first plant peptide hormone shown to activate systemic defense responses. His work helped establish the role of peptide signals in plant defense and plant–insect interactions.

Ryan was elected to the United States National Academy of Sciences in recognition of his contributions to plant biochemistry and signaling.

Early life and education Clarence A. Ryan was born in 1920 in the United States. He trained as a biochemist and developed a research career focused on plant physiology and plant–insect interactions. Ryan later joined the faculty at Washington State University, where he became a professor in the Institute of Biological Chemistry and conducted research on plant defense mechanisms.

Subsequent work demonstrated that systemin is produced from a larger precursor protein known as prosystemin. Ryan's group showed that antisense suppression of the gene strongly reduced systemic wound responses, confirming that systemin functions as a central signaling molecule in plant defense pathways.

The discovery of systemin demonstrated that plants use peptide signals to communicate damage information between tissues and activate defensive genes.

Honors and recognition Ryan received numerous honors for his contributions to plant biochemistry and plant defense signaling. Ryan's later discovery of the peptide signaling molecule systemin in 1991 provided a molecular explanation for this systemic wound signaling pathway and became one of the most influential findings of his career.

Ryan received the Stephen Hales Prize from the American Society of Plant Physiologists in 1992 in recognition of his research on plant defense mechanisms.

In 2007 he was named a member of the inaugural class of ASPB Fellows.