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Plant Biology

Molecular Sunscreen

An international group of researchers, including scientists from CNRS and CEA,1 has identified one of the biochemical mechanisms used by plants to protect themselves from excessive sunlight and environmental stresses such as dryness.
Located inside the plant chloroplast membrane, the antenna system is a complex of many different proteins whose role is to absorb light and transfer it to photosystems where it is transformed into chemical energy. However, when a plant receives too much sunlight or experiences an external stress like dryness, these same proteins can turn into energy “diffusers” to protect the plant, turning energy into heat. “In ideal conditions, when light isn’t too intense–a cloudy day, for instance–plants maximize their total capture surface,” says co-author Bruno Robert. “But when light intensity grows, this intrinsic feedback regulator mechanism informs the antenna proteins that they have captured more photons than can be used for photosynthesis.” Too much energy could lead to the over-production of free radicals, which are toxic for the plant.
In 2005, the team had identified two conformations of the major antenna protein in vitro, and suggested these could be linked to the two functional states of the protein. In their latest in vivo study,2 the team verified this hypothesis by exposing Arabidopsis thaliana plants to different intensities of light. Using structural spectroscopy, they recorded in vivo the conformational changes of antenna proteins associated with variations in light intensity. Rapid spectroscopy then enabled them to observe that it is lutein–one of the major antenna protein’s three carotenoid co-factors–that is converting excitation energy into heat.
“There are many regulation mechanisms–some plants orient their leaves according to sunlight, but there can also be chloroplastic movements inside the cells. This molecular regulation system is the one adapted to immediate and subtle changes of light exposure, and takes place within a few seconds,” says Robert. These fundamental findings could lead to applications in various fields, the authors point out. In agriculture, for instance, decreasing the plants’ photo-protection mechanism could help increase production.

Clémentine Wallace

Notes :

1. Institut de biologie et de technologies de Saclay (CEA).
2. A.V. Ruban et al., “Identification of a mechanism of photoprotective energy dissipation in higher plants,” Nature, 2007. 450: 575-78.

Contacts :

Bruno Robert
CEA, Gif sur Yvette.


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