Plant physiology

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The plant physiology is the science of life processes ( physiology ) of the plant . Photosynthesis is a central process , followed by the formation of other substances (from glucose to polysaccharides to lipids , proteins and nucleic acids ). In addition, growth processes, the differentiation of organs, reactions to environmental stimuli, substance transport and communication between cells, tissues and organs are examined.

Sub-areas

The Strasburg textbook of plant sciences distinguishes five sub-areas of physiology that often overlap:

history

Antiquity to the 18th century

The earliest observations on the physiology of plants have come down to us from antiquity . The botanical writings of Aristotle , whose zoological work was decisive for 1800 years, have been lost. However, those of his pupil Theophrast (371–285 BC) on the causes of plant growth were preserved , in which the effects of the climate and the nature of the soil on growth are described and also the leaf movements of the mimosa and the tamarind are shown.

Stephen Hales

Aristotle assumed that the plant takes its food from the earth and that this is perfect, since unlike animals and humans, no excrement is excreted. These and other views of Aristotle and Theophrastus were only passed on for a very long time. It was not until 1671 that Marcello Malpighi subjected Aristotle's teaching to an examination, whereby he came to the result based on experiments that the nutrient juice in the leaves is processed ("boiled out") by the power of sunlight and only then can it cause growth. The physicist Edme Mariotte (1679) contributed another important thought by considering the sap pressure, which can be observed , for example, when milk sap flows out , as the physical cause of growth. Stephen Hales , a student of Isaac Newton , with his Vegetable Staticks (1727, German: Statick der Gewächse , 1748) can be regarded as the actual founder of experimental plant physiology . He was the first to conduct systematic series of tests on the water balance of plants and on evaporation ( transpiration ) and stated that it is not the sap pressure emanating from the roots, but the transpiration of the leaves that mainly causes the sap flow.

Jan Ingenhousz

Further advances in this area were only possible after Joseph Priestley and Antoine Laurent de Lavoisier discovered in the 1770s that the air contains oxygen (" living air ") and "carbonic acid" ( carbon dioxide ), and that the latter is made up of carbon and oxygen. Priestley had observed that a burning candle in a closed vessel made the air unfit to breathe and that a plant brought in made it again suitable for breathe and for burning. This contrasted with the experimental postulate of Carl Wilhelm Scheele that plants degrade the air. The doctor Jan Ingenhousz was able to resolve this contradiction in 1779: It is not the growth of the plant but its green leaves that form oxygen, and not in the dark, but only in the light. Ingenhousz had thus clarified the connection between photosynthesis and respiration at the level of gas exchange. In another publication in 1796, he stated that the plant takes the carbon from the carbon dioxide it has absorbed as food and "exhales" the oxygen.

19th and 20th centuries

At the beginning of the 19th century, Ingenhousz was followed by Nicolas-Théodore de Saussure with investigations that primarily focused on quantitative, i.e. measurable, relationships. He found that the increase in the dry matter of the plant is higher than the absorption of carbon from the air, and concluded that components of the water are also bound. (According to current knowledge, the water itself, which forms carbohydrates with carbon .) In contrast, only a small part of the dry matter comes from the soil. This is still necessary because plants cannot grow normally in distilled water. And de Saussure also demonstrated that plants cannot use the nitrogen in the air, but have to absorb it from the ground.

Many new discoveries were made by Henri Dutrochet in the early 19th century . This includes his studies on the importance of osmosis and the function of the stomata on the underside of the leaves. He showed that the intercellular space of some plant tissues is permeable to air and that in pond roses there is an exchange of gas from the stomata to the roots (the stomata here exceptionally sit on the upper side of the floating leaves). He also made a distinction between the osmosis-induced flow of juice that Mariotte had examined and the ascent of the juice examined by Hales. He also made it clear that the plasma flow within the cells has nothing to do with the ascent of the sap.

Up until the middle of the 19th century, these experimental investigations were largely countered by speculative notions, according to which life processes are based on a “life force” ( vitalism ) and that the living can only emerge from the living. This included the humus theory going back to Aristotle , which was particularly represented by Albrecht Thaer and postulated that the plant feeds on humus . Such ideas remained prevalent for decades, despite research by de Saussure and others. The turning point brought a work by Justus von Liebig (1840) in which he formulated a mineral theory and underpinned this by using mineral fertilizers in agricultural experiments. Liebig, however, wrongly assumed that the plant took nitrogen from the atmosphere, which Jean-Baptiste Boussingault (1843/44) refuted. After he noticed that plants grow particularly well on plots that had been tilled with legumes the year before , Boussingault demonstrated that these (unlike cereals) can assimilate atmospheric nitrogen. It was not until 1888 that it became clear that this was an achievement of bacteria in the leguminous root nodules.

Julius Sachs

The most important plant physiologist in the second half of the 19th century was Julius Sachs . He introduced hydroponics to study the function of the roots and to determine which chemical elements are necessary for plant growth in the root space. He discovered that the water and nutrients are absorbed through the fine root hairs . He also identified starch as a product of photosynthesis and found out that it accumulates in the chloroplasts during the day (in the light) and is broken down again at night (in the dark). When starchy seeds germinate, he investigated the breakdown of starch, and he showed that guard cells and root tips contain starch even if it has disappeared in other parts of the plant. His textbooks on botany and plant physiology achieved great importance, also as English translations.

Wilhelm Pfeffer

In the late 19th century, the interest of plant physiologists increasingly shifted to the cell level, mainly thanks to the work of Wilhelm Pfeffers , who referred to and from the protoplast , the interior of the plant cell (without the cell wall ), as the plant "elementary organism" and wanted to investigate physiology from its parts. At the same time, the previously only descriptive and comparative morphology was partly transformed into a “ causal morphology” which looked experimentally for the causes of plant formation. Here Karl von Goebel became the most important representative. Likewise, in the anatomy , the examination of the tissue, causal questions came to the fore, especially by Gottlieb Haberlandt .

In the direction initiated by Pfeffer, research on plant physiology experienced an enormous upswing in the 20th century; the number of publications appearing every year multiplied. In the context of the new concepts of quantum physics , a discussion arose in the 1930s about possible limits to the causal explicability of life processes, which was initiated in particular by the theoretical physicists Pascual Jordan and Niels Bohr . Jordan formulated an amplifier theory of organisms , according to which the unpredictable behavior of electrons , as occurs in quantum physics experiments, causes an indeterminacy of macrophysical events and thus of life processes in cells as in an amplifier . Bohr applied the principle of complementarity he established to biology with similar consequences . Erwin Bünning and Erwin Schrödinger particularly opposed this. With the advances in biochemistry and the establishment of molecular biology in the 1950s, these speculations lost their plausibility. The decisive factor was not theoretical considerations or new concepts, but numerous new experimental techniques.

See also

literature

Web links

Wiktionary: Plant Physiology  - explanations of meanings, word origins, synonyms, translations

Individual evidence

  1. ^ Joachim W. Kadereit, Christian Körner, Benedikt Kost, Uwe Sonnewald: Strasburger Textbook of Plant Sciences . 37th edition, Springer Spectrum, Berlin / Heidelberg 2014, p. 334.
  2. ^ Karl Mägdefrau: History of Botany . Gustav Fischer, Stuttgart 1973. pp. 5-7.
  3. ^ Karl Mägdefrau: History of Botany . Gustav Fischer, Stuttgart 1973. pp. 80-84.
  4. ^ Karl Mägdefrau: History of Botany . Gustav Fischer, Stuttgart 1973. pp. 84-86.
  5. ^ Karl Mägdefrau: History of Botany . Gustav Fischer, Stuttgart 1973. pp. 86f.
  6. ^ Karl Mägdefrau: History of Botany . Gustav Fischer, Stuttgart 1973. pp. 87-89.
  7. ↑ Ilse Jahn (Ed.): History of Biology . 3rd edition, Nikol special edition, Hamburg 2004, p. 319f.
  8. ^ Karl Mägdefrau: History of Botany . Gustav Fischer, Stuttgart 1973. pp. 206-211.
  9. ↑ Ilse Jahn (Ed.): History of Biology . 3rd edition, Nikol special edition, Hamburg 2004, pp. 499–501.
  10. ↑ Ilse Jahn (Ed.): History of Biology . 3rd edition, Nikol special edition, Hamburg 2004, pp. 502–508.