André Tridon Jagendorf (October 21, 1926 – March 13, 2017) was an American Liberty Hyde Bailey Professor Emeritus in the Section of Plant Biology[1][2][3] at Cornell University who is notable for providing direct evidence that chloroplasts synthesize adenosine triphosphate (ATP) using the chemiosmotic mechanism proposed by Peter Mitchell.

André Jagendorf graduated from Cornell University, where he was strongly influenced by Loren Petry, who taught General Botany.

[7][8] André then went to UCLA, where he was awarded a Merck Postdoctoral fellowship and spent what he called "the happiest years of my life" working with Sam Wildman.

Since 1997 Jagendorf has been the Liberty Hyde Bailey Professor Emeritus in the Department of Plant Biology and was actively doing research and mentoring young scientists until days before his death.

Later that summer Jagendorf did the experimentum crucis that showed that the synthesis of adenosine trisphosphate by chloroplasts depended on the magnitude of the pH difference.

[15] According to Berg et al. "This incisive experiment was one of the first to unequivocally support the hypothesis put forth by Peter Mitchell that ATP synthesis is driven by proton-motive force.

"[16] Following Jagendorf's results, Mitchell wrote a letter to Edward C. Slater on November 2, 1965, stating: "experiments have been steadily pushing me towards accepting the chemiosmotic hypothesis and I think I shall feel inclined presently to regard it as a theory.

According to Tom Sharkey, André Jagendorf, a brilliant and an original scientist has made seminal contributions to the development of photophosphorylation and the elucidation of its mode of action.

In view of the prevailing theory that assumed the involvement of a hypothetical phosphorylated intermediate and the lack of credible experimental results in support of the chemiosmotic hypothesis his experiment revolutionized the field.