Plant physiology

Plant physiology as a science has recent origins; however, observations on plant life phenomena are already found among the ancients. Aristotle and his disciple Theophrastus, author of De causis plantarum, held that plants drew nutrients from the earth already in a directly assimilable form. This conception, taken up in part by Cesalpinus, practically dominated until the 16th century, when, making use of advances in chemistry and physics, the first studies on an experimental basis were initiated on the process of plant nutrition, sap circulation and transport of substances in solution form. J. B. van Helmont, based on his experiences, believed that the various constituents of plants were manufactured by the plants themselves.

E. Mariotte attempted to trace plant nutrition and growth back to chemical or physical processes. Fundamental to the development of plant physiology was the work of S. Hales, who carried out a series of systematic experiments on the problem of sap circulation, especially highlighting the role played by leaf transpiration and discovering root pressure. The function of chlorophyll was highlighted in the late 18th century by J. Priestley who demonstrated that green plants are capable of emitting “vital air,” that is, oxygen. G. Ingenhousz complemented this observation by noting that only the green parts of plants and only in light perform “vital air,” and later gave the exact interpretation of the phenomenon by making use of the findings of A.-L. Lavoisier.

The set of gaseous exchanges that take place in plants were further specified by J. Sebenier, who recognized that carbon dioxide is broken down by plants, under the influence of light, with the emission of oxygen. At the beginning of the 19th century T. de Saussure performed precise experiments that made it possible to evaluate in quantitative terms the phenomena occurring during nutrition. H. Dutrochet discovered the fundamental laws governing permeability and the phenomena of osmosis, later also specified by W. Pfeffer.

Plant physiology drew new impetus from the studies of J. Sachs, who, in a group of papers published between 1860 and 1865, recognized the general significance of photosynthetic processes and clarified how and where the organization of carbon dioxide to the formation of starch occurs. Research around mineral nutrition was initiated by J. Liebig and later by J.-B. Boussingault, who demonstrated the importance of nitrogenous substances, and especially nitrates, for plant life. In 1887 H. Helbriegel and H. Wilfarth discovered biological nitrogen fixation.

With the 20th century, a new period for plant physiology began: common phenomena that had gone unnoticed (photoperiodicity) as well as the existence of hereditary physiological characters were discovered; developmental regulatory substances were isolated; many enzymes were discovered; and, using the technique of labeled elements and chromatography, the process of photosynthesis was elucidated. It is difficult, however, to make a separation between plant physiology and biochemistry, sciences that, together with genetics, have increasingly contributed to the rise of molecular biology, while the links between plant physiology and ecology become closer.

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