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Thorsten Ritz

Publications and source records attributed to Thorsten Ritz.

10 recordsLinked to original sources
PubMed2006

Magnetic intensity affects cryptochrome-dependent responses in Arabidopsis thaliana.

Cryptochromes are blue-light absorbing photoreceptors found in many organisms where they have been involved in numerous growth, developmental, and circadian responses. In Arabidopsis thaliana, two cryptochromes, CRY1 and CRY2, mediate several blue-light-dependent responses including hypocotyl growth inhibition. Our study shows that an increase in the intensity of the ambient magnetic field from 33-44 to 500 muT enhanced growth inhibition in A. thaliana under blue light, when cryptochromes are the mediating photoreceptor, but not under red light when the mediating receptors are phytochromes, or in total darkness. Hypocotyl growth of Arabidopsis mutants lacking cryptochromes was unaffected by the increase in magnetic intensity. Additional cryptochrome-dependent responses, such as blue-light-dependent anthocyanin accumulation and blue-light-dependent degradation of CRY2 protein, were also enhanced at the higher magnetic intensity. These findings show that higher plants are sensitive to the magnetic field in responses that are linked to cryptochrome-dependent signaling pathways. Because cryptochromes form radical pairs after photoexcitation, our results can best be explained by the radical-pair model. Recent evidence indicates that the magnetic compass of birds involves a radical pair mechanism, and cryptochrome is a likely candidate for the avian magnetoreception molecule. Our findings thus suggest intriguing parallels in magnetoreception of animals and plants that appear to be based on common physical properties of photoexcited cryptochromes.

Anthocyanins↗
PubMed2006

The magnetic compass mechanisms of birds and rodents are based on different physical principles.

Recently, oscillating magnetic fields in the MHz-range were introduced as a useful diagnostic tool to identify the mechanism underlying magnetoreception. The effect of very weak high-frequency fields on the orientation of migratory birds indicates that the avian magnetic compass is based on a radical pair mechanism. To analyse the nature of the magnetic compass of mammals, we tested rodents, Ansell's mole-rats, using their tendency to build their nests in the southern part of the arena as a criterion whether or not they could orient. In contrast to birds, their orientation was not disrupted when a broad-band field of 0.1-10MHz of 85nT or a 1.315MHz field of 480nT was added to the static geomagnetic field of 46000nT. Even increasing the intensity of the 1.315MHz field (Zeeman frequency in the local geomagnetic field) to 4800nT, more than a tenth of the static field, the mole-rats remained unaffected and continued to build their nests in the south. These results indicate that in contrast to that of birds, their magnetic compass does not involve radical pair processes; it seems to be based on a fundamentally different principle, which probably involves magnetite.

Animals↗
PubMed2005

Two different types of light-dependent responses to magnetic fields in birds.

A model of magnetoreception proposes that the avian magnetic compass is based on a radical pair mechanism, with photon absorption leading to the formation of radical pairs. Analyzing the predicted light dependency by testing migratory birds under monochromatic lights, we found that the responses of birds change with increasing intensity. The analysis of the orientation of European robins under 502 nm turquoise light revealed two types of responses depending on light intensity: under a quantal flux of 8.10(15) quanta m(-2) s(-1), the birds showed normal migratory orientation in spring as well as in autumn, relying on their inclination compass. Under brighter light of 54.10(15) quanta m(-2) s(-1), however, they showed a "fixed" tendency toward north that did not undergo the seasonal change and proved to be based on magnetic polarity, not involving the inclination compass. When birds were exposed to a weak oscillating field, which specifically interferes with radical pair processes, the inclination compass response was disrupted, whereas the response to magnetic polarity remained unaffected. These findings indicate that the normal inclination compass used for migratory orientation is based on a radical-pair mechanism, whereas the fixed direction represents a novel type of light-dependent orientation based on a mechanism of a different nature.

Animal Migration↗
PubMed2005

Magnetoreception and its use in bird navigation.

Recent advances have brought new insight into the physiological mechanisms that enable birds and other animals to use magnetic fields for orientation. Many birds seem to have two magnetodetection senses, one based on magnetite near the beak and one based on light-dependent radical-pair processes in the bird's eye(s). Among the most exciting recent results are: first, behavioural responses of birds experiencing oscillating magnetic fields. Second, the occurrence of putative magnetosensory molecules, the cryptochromes, in the eyes of migratory birds. Third, detection of a brain area that integrates specialised visual input at night in night-migratory songbirds. Fourth, a putative magnetosensory cluster of magnetite in the upper beak. These and other recent findings have important implications for magnetoreception; however, many crucial open questions remain.

Animal Migration↗
PubMed2004

Magnetic compass orientation of migratory birds in the presence of a 1.315 MHz oscillating field.

The radical pair model of magnetoreception predicts that magnetic compass orientation can be disrupted by high frequency magnetic fields in the Megahertz range. European robins, Erithacus rubecula, were tested under monochromatic 565 nm green light in 1.315 MHz fields of 0.48 microT during spring and autumn migration, with 1.315 MHz being the frequency that matches the energetic splitting induced by the local geomagnetic field. The birds' responses depended on the alignment of the oscillating field with respect to the static geomagnetic field: when the 1.315 MHz field was aligned parallel with the field lines, birds significantly preferred northerly directions in spring and southerly directions in autumn. These preferences reflect normal migratory orientation, with the variance slightly increased compared to control tests in the geomagnetic field alone or to tests in a 7.0 MHz field. However, in the 1.315 MHz field aligned at a 24 degrees angle to the field lines, the birds were disoriented in both seasons, indicating that the high frequency field interfered with magnetoreception. These finding are in agreement with theoretical predictions and support the assumption of a radical-pair mechanism underlying the processes mediating magnetic compass information in birds.

Animal Migration↗
PubMed2004

Excitation migration in trimeric cyanobacterial photosystem I.

A structure-based description of excitation migration in multireaction center light harvesting systems is introduced. The description is an extension of the sojourn expansion, which decomposes excitation migration in terms of repeated detrapping and recapture events. The approach is applied to light harvesting in the trimeric form of cyanobacterial photosystem I (PSI). Excitation is found to be shared between PSI monomers and the chlorophylls providing the strongest respective links are identified. Excitation sharing is investigated by computing cross-monomer excitation trapping probabilities. It is seen that on the average there is a nearly 40% chance of excitation cross transfer and trapping, indicating efficient coupling between monomers. The robustness and optimality of the chlorophyll network of trimeric PSI is examined.

Chlorophyll↗
PubMed2004

Resonance effects indicate a radical-pair mechanism for avian magnetic compass.

Migratory birds are known to use the geomagnetic field as a source of compass information. There are two competing hypotheses for the primary process underlying the avian magnetic compass, one involving magnetite, the other a magnetically sensitive chemical reaction. Here we show that oscillating magnetic fields disrupt the magnetic orientation behaviour of migratory birds. Robins were disoriented when exposed to a vertically aligned broadband (0.1-10 MHz) or a single-frequency (7-MHz) field in addition to the geomagnetic field. Moreover, in the 7-MHz oscillating field, this effect depended on the angle between the oscillating and the geomagnetic fields. The birds exhibited seasonally appropriate migratory orientation when the oscillating field was parallel to the geomagnetic field, but were disoriented when it was presented at a 24 degrees or 48 degrees angle. These results are consistent with a resonance effect on singlet-triplet transitions and suggest a magnetic compass based on a radical-pair mechanism.

Animal Migration↗
PubMed2002

Shedding light on vertebrate magnetoreception.

We review the challenges and recent progress in elucidating the physiological basis of animal magnetoreception. Behavioral and theoretical studies suggest a link between photoreception and magnetoreception in some animals. Neurophysiological studies have the potential to prove this link and identify the location of and the mechanism underlying the magnetoreception system.

Animal Migration↗
PubMed2002

The quantum physics of photosynthesis.

Biological cells contain nanoscale machineries that exhibit a unique combination of high efficiency, high adaptability to changing environmental conditions, and high reliability. Recent progress in obtaining atomically resolved structures provide an opportunity for an atomic-level explanation of the biological function of cellular machineries and the underlying physical mechanisms. A prime example in this regard is the apparatus with which purple bacteria harvest the light of the sun. Its highly symmetrical architecture and close interplay of biological functionality with quantum physical processes allow an illuminating demonstration of the fact that properties of living beings ultimately rely on and are determined by the laws of physics.

Carotenoids↗