Photosynthesis: a short history of some modern experimental approaches.

This paper presents a personal interpretation of a chapter of plant physiology beginning from the early 1930s to the early 1940s, when plant physiologists tried to find the missing link between the two (dark and light) phases of photosynthesis. As initially inferred by Richard Willstätter and Arthur Stoll in the 1910s, and then stated by Robert Emerson and William Arnold in 1932, the most accredited theory proposed that carbon dioxide must combine with chlorophyll in the dark. Successive light flashes activated the complex chlorophyll-carbon dioxide with oxygen evolution, and carbon dioxide was reduced to formaldehyde and successively polymerised into hexose. Arthur Stool in 1932 and Cornelius v. Niel in 1935 gave the first stroke to this theory suggesting that carbon dioxide must be reduced and assimilated by means of a process of water oxidation. Robert Hill showed the existence of an indissoluble link between the light phase, water oxidation and possibly oxygen evolution. Two physicists, Sam Ruben and Martin Kamen proposed the assembly of photosynthesis into a unitary process occurring as a sequence of several steps in the first 1940s. By utilising for the first time radioactive carbon (11C), they elaborated a new theory according to which carbon dioxide reduction was a repeated "cyclic" mechanism. This "heretical" view abolished the old, but still considered, theory of formaldehyde. Hill, Ruben and Kamen were able to exploit at best the possibility offered by a very advanced technology, thus confirming once again that ideas stand upon the powerful legs of technology.