Theory Exploded

In grotesque fragments last week lay a venerable theory which sought to explain the most important chemical reaction on earth: photosynthesis. Theory-busters were a group of young biochemists, headed by Samuel Ruben, at the University of California. They have penetrated deeper than anyone so far into the mysterious process by which the sun's energy pouring earthward in the form of light is captured by chlorophyll and stored as carbohydrates, the basic food of animal life.

Green plants take water, carbon dioxide (from the air) and energy (from light), transform them with the help of chlorophyll into carbohydrates and free oxygen. The chemical form for this reaction is:

6CO₂ + 6H₂O + 673 calories ->> C₆H₁₂O₆ + 6O₂

This tells what goes in and what comes out. The mystery is how the transmutation is achieved. The classic explanation, commonly accepted until recently, was proposed in 1870 by Johann Friedrich Wilhelm Adolf von Baeyer, and amplified by Nobel Prizeman Richard Willstuetter of Munich: Under the influence of chlorophyll, carbon dioxide and water combine to form formaldehyde (CH₂O) and free oxygen. Then, under the influence of light, six formaldehyde molecules somehow assemble into one glucose molecule:

6CH₂O ->>C₆H₁₂O₆

Unimpressed with this explanation was Biochemist Cornelis Bernardus van Niel of Stanford. "Forget about sugar," he told his students. "Consider the other end-product--oxygen. Where does it come from? Discover that and you will be closer to the whole solution." Dr. Ruben at California took this line.

Hitch was that both the raw materials of photosynthesis, H₂O and CO₂, contain identical oxygen atoms. There was no way of telling them apart. So Ruben obtained heavy oxygen--a rare isotope which has a mass of 18 instead of the normal atomic weight of 16--and made from it heavy-oxygen water. This was fed to a green plant, together with ordinary, light-oxygen carbon dioxide. As photosynthesis proceeded, the scientists caught the freed oxygen, found it was the heavy variety. Next they fed the plant light-oxygen water and heavy-oxygen carbon dioxide. All the oxygen thus freed was light. So it was proved that all the free oxygen comes directly from the water. Under the old formaldehyde theory, the intermediate equations made it appear that all the free oxygen came from the carbon dioxide.

In a similar "tracer" experiment, Ruben & Co. introduced radioactive carbon into plants (TIME, June 23), were later unable to find any radioactive formaldehyde in them. (Formaldehyde is poisonous to plants, anyway.) This was another blow to the old theory.

Synthetic photosynthesis. Another attack on this problem is described in a recent book, Photosynthesis (Van Nostrand; $4.75), by Edward Charles Cyril Baly, Emeritus Professor of Chemistry at the University of Liverpool.

Baly records some curious experiments. In his laboratory in 1928 he achieved the photosynthesis of formaldehyde, glucose, starch, other organic compounds in a test-tube solution of carbon dioxide. As a catalyst he used nickel carbonate instead of chlorophyll (which no chemist has yet got to work outside the veins of plants). But neither Baly nor any other chemist, using identical methods, has ever succeeded in repeating the experiment.

Baly next succeeded in laboratory photosynthesis with nickel oxide. He is much impressed by similarities between his nickel-catalyzed photosynthesis and the natural chlorophyll-catalyzed process. Both act alike under variations of light and temperature.

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