Secrets from Sunlight

How do green plants manufacture food and store energy by absorbing carbon dioxide, water and sunlight? Scientists have been piecing together the answer for years, sure that when they learn the last detail of the complicated process they will be closer than ever before to understanding the secret heart of nature. For life itself--in whatever form it appears on earth--steadily expends the solar energy stored during the intricate chemical reaction that scientists call photosynthesis.

Some of the mystery began to come clear in 1938 after researchers learned to use isotopes to trace the transformation from water and carbon dioxide to sugar and oxygen. But how does light start the process? In the British scientific journal Nature, two University of California biochemists, Drs. Kunio Tagawa and Daniel Arnon, report that they have moved closer than ever before to a satisfactory answer.

The Berkeley researchers made a significant breakthrough eight years ago when they learned that tiny bodies (chloro-plasts) from plant cells can carry on photosynthesis all by themselves. Using isolated chloroplasts from spinach leaves, Dr. Arnon and his colleagues found that they could study the role of light without being bothered by the other chemical processes that take place in the normal plant cell. After tedious experiment, they decided that when green plant pigment (chlorophyll) is struck by sunlight its molecules become so excited that they shake loose some electrons. And those electrons eventually help to form some of the basic chemical substances necessary for photosynthesis.

The scientists checked their theory by searching for some other source of the all-important electrons. Under experimental conditions, they tried hydrogen gas--a rich source of electrons itself--and discovered that it did the job perfectly. For the first time, man had triggered photosynthesis without using light.

Now, in laboratories all over the world, other researchers are designing experiments to exploit this new knowledge of photosynthesis. Drs. Arnon and Tagawa have already been able to recognize a striking similarity between photosynthesis in plants and chemical processes that are carried on by certain bacteria that live in the soil, cut off from both sunlight and oxygen. The discovery, says Dr. Arnon, demonstrates "the beautiful biochemical unity of nature."

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