Erwin Bünning
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Erwin Bünning (23 January 1906 – 4 October 1990) was a German
biologist A biologist is a scientist who conducts research in biology. Biologists are interested in studying life on Earth, whether it is an individual Cell (biology), cell, a multicellular organism, or a Community (ecology), community of Biological inter ...
. His most famous contributions were to the field of chronobiology, where he proposed a model for the
endogenous Endogeny, in biology, refers to the property of originating or developing from within an organism, tissue, or cell. For example, ''endogenous substances'', and ''endogenous processes'' are those that originate within a living system (e.g. an ...
circadian rhythm A circadian rhythm (), or circadian cycle, is a natural oscillation that repeats roughly every 24 hours. Circadian rhythms can refer to any process that originates within an organism (i.e., Endogeny (biology), endogenous) and responds to the env ...
s governing plant photoperiodism. From these contributions, Bünning is considered a co-founder of chronobiology along with Jürgen Aschoff and
Colin Pittendrigh Colin Stephenson Pittendrigh (October 13, 1918 – March 19, 1996)
"Colin Pittendrigh, 'Father of biological clock,' ...
.


Life


Early life and education

Bünning was born on 23 January 1906 in
Hamburg Hamburg (, ; ), officially the Free and Hanseatic City of Hamburg,. is the List of cities in Germany by population, second-largest city in Germany after Berlin and List of cities in the European Union by population within city limits, 7th-lar ...
, Germany to Heinrich Bünning and Hermine Bünning (born Winkler). A teacher of German, English, mathematics, and biology, Bünning's father was the primary academic influence on Erwin's early life, passing on to Erwin a passion for
botany Botany, also called plant science, is the branch of natural science and biology studying plants, especially Plant anatomy, their anatomy, Plant taxonomy, taxonomy, and Plant ecology, ecology. A botanist or plant scientist is a scientist who s ...
. Bünning received his primary education in Hamburg from 1912-1925. Bünning then attended the
University of Göttingen The University of Göttingen, officially the Georg August University of Göttingen (, commonly referred to as Georgia Augusta), is a Public university, public research university in the city of Göttingen, Lower Saxony, Germany. Founded in 1734 ...
and the
University of Berlin The Humboldt University of Berlin (, abbreviated HU Berlin) is a public research university in the central borough of Mitte in Berlin, Germany. The university was established by Frederick William III on the initiative of Wilhelm von Humbol ...
from October 1925-July 1928, where he studied biology, chemistry, physics, and philosophy. Bünning earned his Doctorate of Philosophy from the
University of Berlin The Humboldt University of Berlin (, abbreviated HU Berlin) is a public research university in the central borough of Mitte in Berlin, Germany. The university was established by Frederick William III on the initiative of Wilhelm von Humbol ...
in May 1929. During this time, Bünning married his wife Eleonore; the two would later have four children.


Academic career

In 1930, Bünning took an assistantship under Otto Renner at the
University of Jena The University of Jena, officially the Friedrich Schiller University Jena (, abbreviated FSU, shortened form ''Uni Jena''), is a public research university located in Jena, Thuringia, Germany. The university was established in 1558 and is cou ...
, then one of Germany's largest botanical institutes. During the rise of the
Nazi Party The Nazi Party, officially the National Socialist German Workers' Party ( or NSDAP), was a far-right politics, far-right political party in Germany active between 1920 and 1945 that created and supported the ideology of Nazism. Its precursor ...
in Germany in the early 1930s, Renner stood in open opposition to the Nazis, publicly defending Jewish scientists. Similarly, Bünning was considered a
communist Communism () is a sociopolitical, philosophical, and economic ideology within the socialist movement, whose goal is the creation of a communist society, a socioeconomic order centered on common ownership of the means of production, di ...
sympathizer, a stance likely influenced by Bünning's father, a
Social Democrat Social democracy is a Social philosophy, social, Economic ideology, economic, and political philosophy within socialism that supports Democracy, political and economic democracy and a gradualist, reformist, and democratic approach toward achi ...
opposed to the Nazis. Bünning's political beliefs created tension between him and some of his students. In response to this tension, Bünning left Jena for a lectureship at the East Prussian
University of Königsberg The University of Königsberg () was the university of Königsberg in Duchy of Prussia, which was a fief of Poland. It was founded in 1544 as the world's second Protestant Reformation, Protestant academy (after the University of Marburg) by Duke A ...
. In 1936, Bünning published his model for plant photoperiodism, wherein he proposed that endogenous (internal) circadian rhythms enable plants to measure day length. Bünning's model of photoperiodism would go largely unnoticed by the scientific community until 1960 when he chaired the 1960 Cold Spring Harbor Symposium on Biological Clocks. There, Colin Pittendrigh drew attention to Bünning's work and named his 1936 model on plant photoperiodism the Bünning hypothesis. In 1938, Bünning spent a year traveling through
Java Java is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea (a part of Pacific Ocean) to the north. With a population of 156.9 million people (including Madura) in mid 2024, proje ...
and
Sumatra Sumatra () is one of the Sunda Islands of western Indonesia. It is the largest island that is fully within Indonesian territory, as well as the list of islands by area, sixth-largest island in the world at 482,286.55 km2 (182,812 mi. ...
. His observations on the islands resulted in the book ''Tropische Regenwalder'' (Tropical Rainforests). Upon his return to Germany in 1939, Bünning was conscripted in the German military (
World War II World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...
). Military authorities appointed Bünning as an associate professor at the
University of Strasbourg The University of Strasbourg (, Unistra) is a public research university located in Strasbourg, France, with over 52,000 students and 3,300 researchers. Founded in the 16th century by Johannes Sturm, it was a center of intellectual life during ...
. After the war, Bünning became a full professor at the
University of Cologne The University of Cologne () is a university in Cologne, Germany. It was established in 1388. It closed in 1798 before being re-established in 1919. It is now one of the largest universities in Germany with around 45,187 students. The Universit ...
in 1945 before moving to the
University of Tübingen The University of Tübingen, officially the Eberhard Karl University of Tübingen (; ), is a public research university located in the city of Tübingen, Baden-Württemberg, Germany. The University of Tübingen is one of eleven German Excellenc ...
the next year (1946), where he stayed until his retirement in 1971. At Tübingen, Bünning entered into the workspace of his role model Wilhelm Pfeffer, the man who postulated in 1875 that the orientation of plants in space changes with the time of day. Bünning would later publish a biography on Pfeffer.


Later life and legacy

Over his career, Bünning published over 260 papers in the fields of plant physiology and general biology, as well as a very popular textbook on plant physiology. Bünning died on 4 October 1990 in Tübingen, Germany, after contracting
pneumonia Pneumonia is an Inflammation, inflammatory condition of the lung primarily affecting the small air sacs known as Pulmonary alveolus, alveoli. Symptoms typically include some combination of Cough#Classification, productive or dry cough, ches ...
. Following his death, the German newspaper '' Schwäbisches Tagblatt'' described Bünning as one of the greatest botanists of the 20th century.


Key contributions


Historical context

Changes in the positioning of plant leaves over the course of the day were observed as early as the 4th century B.C. by Androsthenes,
Alexander the Great Alexander III of Macedon (; 20/21 July 356 BC – 10/11 June 323 BC), most commonly known as Alexander the Great, was a king of the Ancient Greece, ancient Greek kingdom of Macedonia (ancient kingdom), Macedon. He succeeded his father Philip ...
’s historian. This phenomenon, however, was not researched further until 1729 when Jean-Jacques d'Ortous de Mairan provided experimental data that mimosa plants close their leaves at night, a movement that persists rhythmically in constant darkness. In 1875, Wilhelm Pfeffer, Bünning’s role model, put forward that these movements might be controlled by an endogenous biological clock. This theory formed the foundation for Bünning’s later work. Prior to Bünning’s work, the prevailing hypothesis on circadian rhythms was the "hourglass" hypothesis, which postulates that circadian rhythmicity within an organism is entirely driven by the external light-dark cycle and that an organism's "hourglass" is reset each day. Bünning, however, proposed that biological clocks are endogenous and synchronize to daily stimuli. Unlike in the hourglass hypothesis, Bünning's hypothesis proposes that circadian rhythmicity derives from an interaction between light and a circadian pacemaker, not external stimuli alone. The general premise of Bünning's hypothesis became a model for circadian time keeping across species off of which many chronobiologists, even into the present, base their models.


Experiments

In the early-1930s, Bünning proposed that organisms rely on a circadian rhythm of sensitivity to light to measure photoperiod. He demonstrated that plants open and close their leaves and insects eclose according to circadian rhythms, even in continuous light or darkness. His crossing experiments with bean plants of different periods in 1935 demonstrated that the next generation had periods of intermediate durations, supporting the suggestion that circadian rhythms are heritable. Bünning also demonstrated that an artificial photoperiod can induce flowering at inappropriate times, supporting his model of endogenous oscillators entrained to external stimuli. To create artificial photoperiods, Bünning exposed plants to a light-dark cycle indicative of a specific season, such as the long days and short nights of summer. By entraining the plants to a spring or summer photoperiod, Bünning was able to induce flowering, even if the actual season were fall or winter. From his results, Bünning proposed that biological clocks have sensors for both light and dark, and their relationship aids photoperiodic timekeeping. His published works provided key synthesis of existing evidence for biological clocks across species, including plants, flies, and fungi. His 1958 work, "The Physiological Clock", was hailed as a milestone in the field of chronobiology, and his later works on plant physiology helped apply his work on photoperiodism to practical uses. In 1935 he demonstrated that plants with different inherent periods would become desynchronized in constant conditions. This work provided evidence for the dismissal of the "Factor X" hypothesis, which held that circadian rhythms were not endogenous, and were instead reliant on an unknown external stimulus, some "Factor X."


Bünning's model

Bünning was the pioneer of the "Bünning Hypothesis," later known as the External Coincidence model. This model proposed a circadian rhythm of photoperiodic photosensitivity in plants. As day length increases with the spring and summer seasons, for example, light hits a plant's photosensitive phase, triggering a physiological or behavioral response. The Bünning Hypothesis proposed that light has two functions for an organism: 1. Light is the primary Zeitgeber for the synchronization of biological rhythms. 2. Light triggers photoinductive responses during certain phases of the circadian cycle.


Honors

Bünning received many honors in his life both in the field of chronobiology and botany. In 1960, he chaired in the 25th Cold Spring Harbor Symposium, "Biological Clocks". The next year, Bünning was elected Corresponding Member of the Botanical Society of America. During his life he was also elected honorary member of the Japanese Botanical Society, the German Botanical Society, the American Society of Plant Physiologists, and the Swiss Botanical Society. He became an elected member of the
American Philosophical Society The American Philosophical Society (APS) is an American scholarly organization and learned society founded in 1743 in Philadelphia that promotes knowledge in the humanities and natural sciences through research, professional meetings, publicat ...
, the
Heidelberg Academy for Sciences and Humanities Heidelberg (; ; ) is the fifth-largest city in the German state of Baden-Württemberg, and with a population of about 163,000, of which roughly a quarter consists of students, it is Germany's 51st-largest city. Located about south of Frank ...
, the
Bavarian Academy of Sciences and Humanities The Bavarian Academy of Sciences and Humanities () is an independent public institution, located in Munich. It appoints scholars whose research has contributed considerably to the increase of knowledge within their subject. The general goal of th ...
, and the German Academy of Scientists, Leopoldina. In addition, he was elected a Foreign Associate of the American
National Academy of Sciences The National Academy of Sciences (NAS) is a United States nonprofit, NGO, non-governmental organization. NAS is part of the National Academies of Sciences, Engineering, and Medicine, along with the National Academy of Engineering (NAE) and the ...
(1968), Foreign Member of the
Royal Society of London The Royal Society, formally The Royal Society of London for Improving Natural Knowledge, is a learned society and the United Kingdom's national academy of sciences. The society fulfils a number of roles: promoting science and its benefits, r ...
, and an Honorary Fellow of the Indian Academy of Sciences (1986). In 1973 Bünning won the Charles Reid Barnes Life Membership Award for "meritorious work in plant biology." The Universities of
Glasgow Glasgow is the Cities of Scotland, most populous city in Scotland, located on the banks of the River Clyde in Strathclyde, west central Scotland. It is the List of cities in the United Kingdom, third-most-populous city in the United Kingdom ...
(1974),
Freiburg Freiburg im Breisgau or simply Freiburg is the List of cities in Baden-Württemberg by population, fourth-largest city of the German state of Baden-Württemberg after Stuttgart, Mannheim and Karlsruhe. Its built-up area has a population of abou ...
(1976), and
Erlangen Erlangen (; , ) is a Middle Franconian city in Bavaria, Germany. It is the seat of the administrative district Erlangen-Höchstadt (former administrative district Erlangen), and with 119,810 inhabitants (as of 30 September 2024), it is the smalle ...
(1977) conferred honorary doctorates on him, as did the
University of Göttingen The University of Göttingen, officially the Georg August University of Göttingen (, commonly referred to as Georgia Augusta), is a Public university, public research university in the city of Göttingen, Lower Saxony, Germany. Founded in 1734 ...
Bünning is considered by many to be the father of the field of chronobiology. His work on measuring the free-running period of plant rhythms and
experiments An experiment is a procedure carried out to support or refute a hypothesis, or determine the efficacy or likelihood of something previously untried. Experiments provide insight into Causality, cause-and-effect by demonstrating what outcome o ...
with cross-breeding strains of plants with different periods aided in the development of that field. Bünning was invited by M. K. Chandrashekaran to
India India, officially the Republic of India, is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area; the List of countries by population (United Nations), most populous country since ...
in 1978, to conduct the Biological Oscillation workshop in Madurai Kamaraj University.


Selected publications

*''Uber die Erblichkeit der Tagesperiodizitat bei den Phaseolus-Blattern'' (1932) *''Die endogene Tagesperiodik als Grundlage der photoperiodischen Reaktion'' (1936) *''Entwicklungs und Bewegungsphysiologie der Pflanze'' (1948) *''In den Waldern Nordsumatras: Reisebuch eines Biologen'' (In the North Sumatran Forests : Travels of a Biologist, 1949) *''Die physiologische Uhr'' ("The Physiological Clock", 1958) *Biological clocks; Chairman's Address; Cold Spring Harbor Symposium (1960) *Interference of Moonlight with the Photoperiodic Measurement of Time by Plants, and their Adaptive Reaction (1969, With Ilse Moser) *''Wilhelm Pfeffer: Apotheker, Chemiker, Botaniker, Physiologe 1845–1920'' (1975) *Pfeffer's views on rhythms (1975, With M K Chandrashekaran) *Fifty years of research in the wake of Wilhelm Pfeffer (1977)


See also

* Chronobiology * Circadian rhythms * Photoperiodism *
Colin Pittendrigh Colin Stephenson Pittendrigh (October 13, 1918 – March 19, 1996)
"Colin Pittendrigh, 'Father of biological clock,' ...
* Jürgen Aschoff


References

{{DEFAULTSORT:Bunning, Erwin 1906 births 1990 deaths 20th-century German biologists Scientists from Hamburg Humboldt University of Berlin alumni University of Göttingen alumni Academic staff of the University of Königsberg Academic staff of the University of Strasbourg Academic staff of the University of Cologne Academic staff of the University of Tübingen Deaths from dementia in Germany Deaths from Alzheimer's disease in Germany 20th-century German botanists Chronobiologists Members of the German Academy of Sciences at Berlin Foreign associates of the National Academy of Sciences International members of the American Philosophical Society