Photosynthesis and Our Study
What is photosynthesis?
Green plants undertake photosynthesis. This is a process by which energy in the sun light drives the conversion of atmospheric carbon dioxide into organic materials. As such, it provides us with most of our living energy and most of our raw materials. Animals do not undertake photosynthesis and all the energy and materials they take come from plants or from other animals which has taken the energy from plants. Thus, all the living organisms on the earth (with very few exceptions), plants, animals and bacteria, depend on the energy in the sun light. You might ask how about coal and oil? Dead plants in ancient times turned into coal, and dead algae to oil, thus both are also the fruits of photosynthesis. Among energy sources on the earth, nuclear power and volcanic power are the only energy sources that do not come from the sun. Photosynthesis has also provided us with the air that we breathe because it produces oxygen as a by-product. Primeval atmosphere contained little oxygen and more carbon dioxide than now. Photosynthesis has changed all this and now we have a great deal of oxygen (about 21%) and very little carbon dioxide (about 0.035%). Our life cannot be maintained without photosynthesis.
Who discovered photosynthesis?
In old days, from the days of Aristotle to 17th century, it was believed that plants grows spontaneously. Then van Helmont proposed that water is necessary for the plant growth (1648). This may be the first turning point in the field of photosynthesis study. Subsequently, Mariotte (1679) and Hales (1727) discovered plants absorb carbon dioxide. Next, the famous experiment of Priestley (1771) came: he demonstrated that plants evolve oxygen which is necessary for animal to breathe. Ingen-Housz (1779) and Senebier (1788) found that the evolution of oxygen requires light energy. Even nowadays, the absorption of carbon dioxide and evolution of oxygen are still used as an efficient way for the detection of photosynthetic activity. In late 19th century, Sachs and his disciple, Pfeffer, found the final product of photosynthesis is starch, and integrate the results of past studies to form the concept of "photosynthetic assimilation". Thus, the most simple description of photosynthesis is:
6CO2 ＋ 6H2O → C6H12O6 ＋6O2
What do we know about photosynthesis now?
The process of photosynthesis can be divided to two phases: one is the electron transfer driven by light to produce biochemical energy source (ATP) and biological reducing power (NADPH) and the other is carbon fixation using ATP and NADPH. Now, almost all the structural proteins involved in the electron transport chain have been identified (see the figure shown below) and their genes sequenced. The reaction center complex in photosynthetic bacteria was crystallized and its 3D-structure was revealed (Michel, Huber and Deisenhofer, Nobel Prize in Chemistry 1988). Theoretical background for electron transfer was given by Marcus, who is also a Nobel Prize Winner in Chemistry 1992. The structure of photosynthetic pigment was already known by 1940 and, concerning this, Nobel Prizes in Chemistry were given to Wilstaetter (1915), Fischer (1930), Karrer (1937), Kuhn (1938) and Woodward (1965). The pathway of the carbon fixation was found by Calvin and coworkers as early as 1950th, and he also won the Nobel Prize in Chemistry 1961. After these excellent works, is there any room to study more?
What is the next question in the study of photosynthesis?
Now, we know almost all the players in the game of photosynthesis. We suppose that the next question is the rules of the game. How is the elaborate machinery of photosynthesis assembled? And how do plants regulate their processes to adapt to different environmental conditions? In our laboratory, we are working hard to answer these questions.