Clarence A. 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.

Scientific career

Ryan’s research focused on how plants respond to insect feeding and mechanical wounding. Earlier studies had shown that wounded plants accumulate defensive proteins, including proteinase inhibitors that interfere with digestive enzymes in herbivorous insects.

In 1991, Ryan and colleagues isolated an 18–amino acid peptide from tomato leaves that triggered the synthesis of wound-inducible proteinase inhibitor proteins.