Contribution to the History of Photosynthesis: de Saussure, Pelletier, Caventou and Dutrochet

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Nicolas Thiodore de Saussure (1767-1845) was of French descent but born in and has since lived in Geneva. He conducted experiments on carbon assimilation in which he disregarded the Phlogiston Theory.

In his Recherches Chimiques sur la Végétation which was published in1804, he showed that the green parts of plants take up and decompose carbon dioxide from the air and at the same time assimilate water. He also found that the process of carbon dioxide decomposition was essential to plant growth and development (Hart 2005). He identified that water was the source of hydrogen and carbon dioxide was the source of plant carbon (Myers 2007).

He therefore confirmed the discoveries of Ingenhousz and Jan Senebier, adding further that the process of photosynthesis requires water as shown in the following equation (Moore et al. 2003):

carbon dioxide + water + light - -> organic material + oxygen

In addition, he found that by artificial means it was possible to increase the concentration of carbon dioxide in the atmosphere sorrounding a plant up to levels that can injure the plant. He measured the amount of carbon fixed by plants and noted that its quantity was lower than the increase in plant weight. He concluded that the plant body was composed mainly of carbon dioxide fixed from the atmosphere with a portion derived from the soil solution.

Along with Jan Ingenhousz and Jean Senebier, he founded the modern theory of plant nutrition. He argued that the minerals composing the ash of plants were not accidental elements taken in with soil water. They are essential to plant growth and development even though they may occur only in extremely small quantities. He also distinguished between two types of essential elements: one is effective in trace amounts while the other is needed in large amounts.

De Saussure likewise studied respiration. He concluded that respiration was necessary to plant growth and that the requirement of plants for oxygen was higher in plant parts which are physiologically active (Hart 2005).

Pierre-Joseph Pelletier (1788-1842), Joseph-Bienaime Caventou (1795–1877) and René-Joachim-Henri Dutrochet (1776–1847).

In 1818, the French chemists Pierre Joseph Pelletier and Joseph Bienaimé Caventou isolated and named chlorophyll, the green pigment in plants that acts as the principal light-absorbing molecule in the process of photosynthesis. The name chlorophyll literally means green leaf. It came from two Greek words: chloros (yellow-green) and phyllon (leaf). The first to recognize the essential role of chlorophyll in photosynthesis was René-Joachim-Henri Dutrochet (1776–1847) in 1837 (Myers 2007).

(Ben G. Bareja. June 2012)

Note: The list of Literature Cited is in the Mainpage.

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