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Daniel Israel Arnon (November 14, 1910 – December 20, 1994) was a Polish-born American plant physiologist and National Medal of Science recipient whose research led to greater insights into the operation of photosynthesis and nutrition in plants.In the first part of his professional career, the so-called "Plant Nutrition Years (1936-1950)", Arnon and collaborators discovered the essentiality of molybdenum for the growth of all plants and of vanadium for the growth of green algae. In the second one, the so-called "Photosynthesis Period (1951-1978)", plant micronutrient work led him to photosynthesis.In 1954, Arnon, Mary Belle Allen and Frederick Robert Whatley discovered photophosphorylation in vitro. In 1967, he was nominated jointly with Allen and Whatley for a Nobel Prize in Chemistry.