Julius von Sachs (1832 -1897). He was a German botanist and physiologist. He achieved fame for his authorship of several books which have been translated to English and became standard textbooks in general botany and plant physiology. He initiated experimental plant physiology and may be regarded as the pioneer in the conduct of studies on the physico-chemical aspects of photosynthesis (Nickelsen 2007).
Reviewed by Govindjee and Krogmann (2004), Sachs showed that starch grains are produced in plant leaves and that these are the first visible product of the process of photosynthesis. He also takes credit for proving that the green pigment chlorophyll in the chloroplast is involved in photosynthesis.
In her 2007 paper From Leaves to Molecules: Botany and the Development of Photosynthesis Research, Kärin Nickelsen explained that the approach in photosynthesis research has undergone a transformation from plant physiology to physico-chemical physiology. It no longer suffices that the plant physiologist be primarily a botanist or zoologist but he or she must be a physicist or chemist capable of understanding the physical and chemical composition of organisms (Nickelsen 2007).
In the same paper, the author described the contribution of Sachs to the history of photosynthesis particularly the functions of the chloroplast and the chlorophyll in photosynthesis; the influence of light intensity on the formation and storage of starch; and the role of starch in plant growth and development. Incidentally, the effect of light intensity on the process of photosynthesis was earlier mentioned by Jan Ingenhousz when he reported in 1779 that the ability of plants to purify the air depended on the brightness of the day.
He experimented on etiolated plants in which he moved them from dark to light. Published in 1862, he concluded that “the chlorophyll grains [= the chloroplasts] are the only and sole place where starch is formed from inorganic matter” and “the embedded starch grains in the chlorophyll are not only a secondary phenomenon but are formed under the influence of a certain light intensity by means of the assimilating action of the latter.” He also found that the production of starch was necessary for plant growth. He noted that plants grew only when they are able to accumulate starch.
Julius von Sachs continued his study and, in 1864, reported that both the production and storage of starch were affected by the exposure of plants to minimum light intensity. He also noted that if a plant or its parts are subsequently moved to a dark place and therefore deprived of sunlight, the starch in the chloroplast would disappear; but if the same plants were again exposed to light, starch production and accumulation ensued. He suggested that plants must behave according to a daily rhythm, that is, plants produce and store starch during the day but at night this same starch is dissolved; it is then transported as sucrose or other forms to other parts of the plant where it is utilized for growth and development (Nickelsen 2007).
Consequently, the overall photosynthetic reaction has been modified as shown (Moore et al. 2003):
nCO2 + nH2O + light ----------> (CH2O) + nO2
Note: The lists of contributors and Literature Cited are in the History of Photosynthesis Mainpage.
(Ben G. Bareja. June 2012)
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