Are quantum effects evidenced in photosynthesis, a form of magnetoreception?

  • 0 Replies

0 Members and 1 Guest are viewing this topic.



  • Guest
In most photo chemical reactions, the generation of geminate radicals produces triplet pairs. A “spinflip” to a reactive singlet pair must occur before the radicals can combine – such a “spinflip” can occur through some magnetic effect in the environment acting on one or both of the spins. 

Radical pair theory predicts if an applied magnetic field perturbs the interconversion of the singlet and triplet states, resulting in an increase in the proportion of the triplet state and thus free radical concentration (Brocklehurst 2002).

Are we seeing this in bacterial photosynthesis where there has been evidence quantum effects, and is it as a result of magnetoreception?
Recent experiments on photosynthetic ‘Light Harvesting Complexes’ (LHC) and their constituents (e.g., the Fenna–Matthews–Olson (FMO) pigment-protein complex in green sulfur bacteria) have suggested that quantum coherence may play a role in one of the most fundamental and important of biological processes: energy transport and energy conversion. N Lambert – ‎2013.

Evidence suggests a wavelike characteristic can explain the extreme efficiency of the energy transfer because it enables the system to simultaneously sample all the potential energy pathways and choose the most efficient one.  This evidence includes detection of “quantum beating” signals, coherent electronic oscillations in both donor and acceptor molecules, generated by light-induced energy excitations.

The fate of triplet excited states in the Fenna-Matthew-Olson (FMO) pigment-protein complex is studied by means of time-resolved nanosecond spectroscopy and exciton model simulations. Experiments reveal microsecond triplet excited-state energy transfer between the bacteriochlorophyll (BChl) pigments, but show no evidence of triplet energy transfer to molecular oxygen, which is known to produce highly reactive singlet oxygen and is the leading cause of photo damage in photosynthetic proteins.  S Kihara - ‎2015

Scientists have demonstrated that a weak magnetic field can impact on the production of a certain molecule found in a photosynthetic bacterium. (Rhodobacter sphaeroides). The bacterium contains a pair of chlorophyll molecules, which allow it to harvest energy from light. But the process relies on a cascade of chemical reactions that can also turn oxygen from the air into a highly reactive form called singlet oxygen, which can damage DNA or proteins in a cell. A magnetic field slightly changes this sequence of reactions by stabilizing a radical molecule formed from chlorophyll that would otherwise generate singlet oxygen.

The scientists removed the photosynthetic molecules from Rhodobacter sphaeroides (R-26) to study them, and found that a magnetic field of 20 millitesla, just 400 times the Earth’s magnetic field, was enough to cut singlet oxygen production by up to 50%. The team also saw that under this magnetic field, the photosynthetic molecules were protected against singlet oxygen damage. Liu Y et al 2005.

A cryptochrome-like protein is involved in the regulation of photosynthesis genes in Rhodobacter sphaeroides. Data reveals that Cryptochrome B in Rhodobacter sphaeroides does not only influence photosynthesis gene expression but also genes for the non-photosynthetic energy metabolism like citric acid cycle and oxidative phosphorylation. In addition several genes involved in RNA processing and in transcriptional regulation are affected by a cryB deletion. Although CryB was shown to undergo a photocycle it does not only affect gene expression in response to blue light illumination but also in response to singlet oxygen stress condition.  Y Geisselbrecht – ‎2012

Cryptochrome in other species has been associated with magnetoreception where it is thought that Magnetic fields can influence the outcome or speed of chemical reactions involving radical pairs by causing flips between the two spin states and by controlling the relative amount of time the molecular players spend in each. Such fluctuations in reactions could in turn provide a chemical cue about the magnetic field.

Based on experimental observations that the high-spin Fe2+ ion affects photosynthetic radical pair reactions, it has been proposed that spin plays a direct role in contributing towards the prevention of destructive events in photosynthetic RCs. This raises the question of whether the effective magnetic field generated by a fast-thermalising spin may play a role in other biological processes, particularly those where magnetic field effects have been observed. A Marais – ‎2015. Also see Marja Hakala-Yatkina et al 2011

More at