Chemists have observed how plants protect themselves from sun damage, For plants, sunlight can be a double edged sword. They need it to drive photosynthesis, the process that allows them to store solar energy as sugar molecules, but too much sun can dehydrate and damage their leaves.
A primary strategy that plants use to protect themselves from this kind of photodamage is to dissipate the extra light as heat.
However, there has been much debate over the past several decades over how plants actually achieve this
In a new study observed, for the first time, one of the possible mechanisms that have been proposed for how plants dissipate energy.
The researchers used a highly sensitive type of spectroscopy to determine that excess energy is transferred from chlorophyll, the pigment that gives leaves their green color, to other pigments called carotenoids, which can then release the energy as heat.
This is the first direct observation of chlorophyll-to-carotenoid energy transfer in the light-harvesting complex of green plants.
When sunlight strikes a plant, specialized proteins known as light-harvesting complexes absorb light energy in the form of photons, with the help of pigments such as chlorophyll. Chemists have observed how plants protect themselves from sun damage.
These photons drive the production of sugar molecules, which store the energy for later use.
Much previous research has shown that plants are able to quickly adapt to changes in sunlight intensity. In very sunny conditions, they convert only about 30 percent of the available sunlight into sugar, while the rest is released as heat.
If this excess energy is allowed to remain in the plant cells, it creates harmful molecules called free radicals that can damage proteins and other important cellular molecules.
The simplest hypothesis for how plants get rid of these extra photons is that once the light-harvesting complex absorbs them, chlorophylls pass them to nearby molecules called carotenoids.
A similar type of energy transfer has been observed in bacterial proteins that are related to chlorophyll, but until now, it had not been seen in plants.
One reason why it has been hard to observe this phenomenon is that it occurs on a very fast time scale (femtoseconds, or quadrillionths of a second).
In this study, the researchers used this technique to show that photons move from an excited state, which is spread over multiple chlorophyll molecules within a light-harvesting complex, to nearby carotenoid molecules within the complex. Chemists have observed how plants protect themselves from sun damage.
They found that the energy transfer occurred more rapidly in the nanodisc, suggesting that environmental conditions affect the rate of energy dissipation.
A better understanding of plants’ natural photoprotection system could help scientists develop new ways to improve crop yields. That paper also suggested that production could be further increased to a theoretical maximum of about 30 percent.