Lichtgedanken 04

S C HW E R P U N K T 19 04 | LICHT GEDANKEN fits—and this is vital knowledge at a time when almost one quarter of working people performs shift work. If the inter- nal clock is disturbed, it can cause harm. Affected people are not just tired; but also more susceptible to illness. Significant correlations between circadian rhythms and the health of the organism in question have been under debate recently. It was about time to acknowledge the scientists who characterized the first clock gene and who have made a decisive contribu- tion to the understanding of the molecular mechanism of the internal clock. What do these findings mean for medicine? That the internal clock shouldn’t be ignored in the treatment process: studies have shown that patients tolerate various medications better at certain times of the day, as the proteins, which contribute to the absorption of the medicines, their dis- tribution and their breakdown, can be controlled by the inter- nal clock. So-called chronotherapy has now been introduced to the treatment of certain cancers as a result; predominantly with the aim of reducing the side-effects of the medication. Getting rid of daylight saving time has once again become a hot topic within the EU. What does changing the clocks mean for the organism? Changing the clocks is basically the equivalent of a mini jet lag for the body. It destroys the activity profile of humans and has to be synchronized again. Lots of people are adversely af- fected by this; some people are more susceptible to depressive moods and the number of accidents increases. Others adapt well to the change and don’t experience any problems. What do you think about getting rid of daylight saving time? Biologically speaking, it would make sense to keep the time the same, so that millions of people do not have to suffer a dis- turbance in their circadian rhythm. Having said that, using mobile phones or certain LED lights around midnight is just as disruptive as changing the clocks. The blue light that they emit is extremely efficient at shifting the phase of our internal clock so we are awake at night and tired during the day. Image left: Expert for micro algae and their internal clock: botanist Maria Mittag. Image right: Culture bottles and petri dishes containing Chlamydomonas reinhardtii . The single-celled green algae have their own »alarm clock« for their day-night rhythm. Maria Mittag and her team of researchers have demonstrated this in a study (original publication under: https://doi.org/10.1104/ pp.17.00349). Chronobiology Chronobiology investigates biological rhythms like the internal daily clock; in other words, it seeks to describe and research the time structure of organisms. Organisms follow a precise, temporal structure in line with events or physiological process­ es that repeat periodically; humans and many other organisms have a circadian rhythm —a daily rhythm, which is around 24 hours long when they are exposed to free-running conditions. It is controlled by the endogenous oscillator or the internal clock. The fact that the leaf movements of some plants follow a circadian rhythm has been known since observations by academics in the 18th century—initially on the mimosa, which closed its leaves and reopened them during both, light-dark experiments and also when in constant darkness (subjective day and subjective night). Algae and light The behaviour of algae is controlled by light in a multitude of ways. They use light as a source of information to synchronize their internal clock, to control their movements and for their sexual cycle. Furthermore, they need light as an energy source for photosynthesis. This is a physiological process where higher plants, algae and some bacteria convert low-energy substances, such as carbon dioxide and water, into high-energy substances with the help of light—oxygen is released as a by- product during this process. The significance of algae Algae, including blue-green algae (cyanobacteria) are respon­ sible for around half of the photosynthetic activity and thus contribute around 50 percent to the CO 2 fixation on Earth. Algae (phytoplankton) also stand at the start of the food chain in the sea and in freshwater: they are eaten by zooplankton, which in turn serves as food for crustaceans, which are then eaten by fish.