Jean-Jacques d’Ortous de Mairan : biography
The following is an abbreviated list of publications (with their English translations) organized by Dr. Robert A. Hatch at the University of Florida:
- Dissertation sur les variations du barometre (Bordeaux, 1715) (Essays on barometric variations)
- (Bordeaux, 1716) (Essay on the ice)
- Dissertation sur la cause de la lumiere des phosphores et des noctiluques (Bordeaux, 1717) (Dissertation on the cause of light phosphates and noctilucence or nightly light)
- (1728) (Essay on the estimation of the measures of forces on the body)
He also published mathematical works.
- , (1733) (Physical and historical Treaty of the aurora borealis)
Experiment on circadian rhythms in plants
In 1729, de Mairan performed an experiment that demonstrated the existence of circadian rhythms in plants, specifically the Mimosa pudica.
He was intrigued by the daily opening and closing of the heliotrope plant and performed a simple experiment where he exposed the plants to constant darkness and recorded the behavior. De Mairan’s key conclusion was that the daily rhythmic opening and closing of the leaves persisted even in the absence of sunlight. However, de Mairan hesitated to conclude that heliotropes have internal clocks and hypothesized that other factors, such as temperature and magnetic fields, were responsible for the rhythmic behavior. He did not publish his results because he doubted his findings and the importance of their implications.
These results may have gone unnoticed had his colleague, Marchant, not published them for de Mairan. The published accounts of de Mairan’s work stimulated further research in the field of chronobiology.
A video showing circadian rhythms in a cucumber plant in constant conditions, similar to what de Mairan observed, can be seen .
de Mairan’s experimental legacy
Despite Marchant’s publication of de Mairan’s work, which was clear evidence for intrinsic circadian oscillations, rhythms in plant movements were thought to be extrinsically controlled, by light and dark cycles, or magnetic and temperature oscillations, for more than thirty years. As more researchers confirmed and replicated de Mairan’s result that plant rhythms persisted in constant darkness it became clear that the rhythms continued even while controlling for other possible influences, such as temperature.
In 1823, over a century later, the Swiss botanist Augustin Pyramus de Candolle expanded on de Mairan’s early theory on the circadian nature of M. pudica by measuring the free running period of plants in constant darkness, finding them to be 22–23 hours long. These results, when considered with the growing experimental evidence of circadian rhythms in many organisms, reinforced the idea that a circadian rhythm could be found in all living organisms, a belief widely held today among chronobiologists.
The circadian nature first described by de Mairan in plants is now evident in a variety of animal models from Drosophila to the common laboratory mouse to humans. Even when describing his work with rhythmic eclosion times in his fly models or running activity of mice, founder of modern chronobiology, Colin Pittendrigh, recognized the work of Jean-Jacques d’Ortous de Mairan. The circadian rhythmicity, which de Mairan first described in Mimosa leaf movements, is now recognized as a feature nearly ubiquitous across all phyla.
In 2011, researchers at the University of Tsukuba in Japan examined an ortholog of Gigantea (GI), a key regulator of the flowering time in plants, to reveal key features of the flowering in plants. They isolated the GI ortholog PnGI from a short period (free running period less than 24 hr.) plant, Pharbitis (Ipomoea) nil. The mRNA expression of this ortholog showed diurnal rhythms that peaked at dusk under short and long day conditions; it also showed circadian rhythms under continuous light and continuous dark conditions. Their data also suggested that PnGI functioned as a suppressor of flowering through its down-regulation of PnFT1, a gene that induces the flower to bud given a single dusk signal.