Plant Photosynthesis

Research in photosynthesis presents and orderly historical development leasing to the present understanding of the process involved.

1. Aristotle and Theophrastus (320 BC) thought that plants derived all their nutrition from plant and animal debris of soil.

2. Van Helmont (1648) said that all food for green plants comes from water. He was one of the first to conduct a real experiment in an attempt to solver the mystery of plant nutrition. Even though, his conclusion was wrong, we can give credit to Van Helmont with starting the enquiry into that link in life’s chain, we now call photosynthesis.

3. Stephen Hales (1727), an illustrious contemporary of Isaac Newton pointed out that green plants may get part of their nourishment through their leaves and sunlight may have something to do with it.

4. Joseph Priestley (1772). He came to the conclusion by his famous experiments on candles, mice and mint that vegetation purifies the air which has been injured by burning of candles. Priestley called the air produced candle as phlogiston and said that plants convert it into dephlogiston. Priestley reported it in an article in Philosophical Transactions (1772), page 53.

…what surprised me most that I cam express, was that a candle burned in this air with a remarkably vigorous flame…I was utterly at a low how to account for it.

Furthermore, when a mouse was placed in a container with this new gas, it lived twice as long as did a mouse in another container of the same size but with air. Priestly breather some of this gas and reported.

My breast felt peculiarly light and easy for sometime afterwards…who can tell but that, in time, this pure air may become a fashionable article in luxury. Hitherto only two mice and myself have had the privilege of breathing it.

The term phlogiston was gradually abandoned after the discovery of oxygen.

5. Ingen-Housz (1779), who was a physician to the emperor of Austria reported that plant purified the air only in the presence of light.

6. Lavoisier (1783) had successfully challenged the phlogiston theory and proposed in its place the theory of oxidation. He identifies the purifying gas produced by plants as oxygen (phlogiston) and noxious gas produced by burning of candle (dephlogiston) as carbon dioxide.

7. Senebier (1782) thought that oxygen which was liberated from the plants in the process came directly from carbon dioxide.

8. De Saussure (1804) discovered that water was used in the process of photosynthesis.

9. Dutrochet (1837) recognized the importance of chlorophyll in photosynthesis.

10. Von Mayer (1845) recognized the importance of light in photosynthesis. Process had been put on the quantitative basis shown in equation.

11. Liebig (1845) reported that sole source of carbon in plants was the carbon dioxide of air.

12. Sachs (1862) found starch as the first visible food.

13. Engelmann (1888) plotted the action spectrum of photosynthesis.

14. Blackman (1905) found that rate of photosynthesis varied with temperature at high light intensity and enunciated the law of limiting factors.

15. Warburg (1920) told the importance of unicellular green alga Chlorella as suitable material for the study of photosynthesis.

16. Van Neil (1931) reported that oxygen is released from photolysis of water and not from CO2.

17. Emerson and Arnold (1932) showed the existence of light and dark reactions by flashing light experiment.

18. Hill (1937). English biochemist R. Hill was the first to get a partial reaction of photosynthesis to work in isolated chloroplasts. His preparations demonstrated the photosynthesis of water by isolated chloroplasts in the presence of light and suitable electron acceptors.

19. Ruben and Kamen (1941). They confirmed that source of oxygen is H2O and not CO2. They used radio isotopic oxygen 18O for this purpose.

20. Arnon, Allen and Whatley (1954) used 14CO2 to show the fixation of CO2 by isolated chloroplasts.

21. M. Calvin (1954) in Berkeley, California using 14CO2 demonstrated the path of carbon in photosynthesis and traced the C3 cycle. He was awarded with noble prize in 1960.

22. Emesrson et. al. (1957) reported the existence of two photo systems.

23. Parka and Sane (9163) Noticed that light reactions occur on thylakoid membranes in grana and dark reaction take place in stroma of the chloroplast.

24. Hatch and Slack (1965) formulated the Hatch and slack cycle of C4 Plants.

25. Kok et al. (1970) discovered that unknown water oxidizing enzyme complex is associated with photo-oxidation of water.

26. Huber, Michel and Dissenhofer (1985) were able to crystallize the photosynthetic reaction center of bacterium Rhizobacter. They analyzed the structure by using X-ray diffraction technique and were awarded with Nobel Prize in chemistry for 1988.