Getting crops to flourish under a cloudy sky

How can we improve plant photosynthesis?

croceCrop yields need to be boosted to feed a world population that will soon reach 9 billion. Roberta Croce, professor of the Biophysics of Photosynthesis and Energy, is investigating possible ways of helping plants to make more efficient use of solar energy, for example by helping photosynthetic systems to respond more flexibly to conditions of sunshine and shade, thus allowing plant growth rates to be increased by up to 20 per cent.

Plants make use of photosynthesis to convert sunlight into chemical energy, which is needed to turn water and carbon dioxide into oxygen and glucose. Glucose is the raw material from which plant tissues are made, so photosynthesis is the ultimate source of all our food. “But plants are not very efficient in making use of solar energy and they are not very fast in adapting to changes in light conditions,” says Prof. Croce. “If after a period of high light they suddenly come to be in the shade, for example because clouds block off the sunlight, it can take up to half an hour for the plant’s photosynthetic system to adapt to the new situation. That’s a pity, because photosynthesis actually works more efficiently in cloudy conditions than in full sunlight.”

Two protein complexes
Prof. Croce’s research group uses physical, biochemical and molecular biology techniques to investigate possible ways of improving crops’ photosynthesis systems. These systems consist of various protein complexes embodying hundreds of pigments that capture solar energy and transform it into chemical energy. The researchers study how these protein complexes work and how the flow of energy is regulated. One important aspect of this is that plants in strong sunlight protect themselves against photodamage by converting the excess absorbed energy into heat. Prof. Croce wants to discover ways of switching off this protection process more quickly when plants are in the shade, since if plants can respond faster to variations in light intensity their photosynthesis systems will be able to produce more chemical energy per unit time, thus allowing the plants to grow faster.

Far-red light
“Another objective of our research is to find ways of helping plants to use a wider range of solar frequencies,” explains Prof. Croce. “At present, plants only convert visible light into chemical energy and hence into food. We know however that the photosynthesis systems in bacteria can also make use of the far-red light from the solar spectrum. We think it should be possible to modify plant genes so that they make use of far-red light too. This would be another way of helping them to grow faster. This will be particulary helpful in the canopy, where the lower leaves only receive far-red light.”

Improving crops
The results of this research can lead to plants and algae able to change the absorption properties of their leaves depending on the light intensity and the light color. When the leaves receive the optimum amount of sunlight, their photosynthesis systems will work more efficiently. In order to promote the exchange of research results, Prof. Croce participated in the Dutch Biosolar cells project for five years. A large number of research centres and companies worked together in this project, which was completed in 2016, to develop ideas about how to improve crops, algae and cyanobacteria, and to make “artificial leaves” – technical systems that mimic the photosynthetic process – to produce biofuels from water and carbon dioxide. “The creation of such consortia allowed us to carry out a combination of fundamental and applied research” Prof. Croce said. “The better we understand the mechanism of photosynthesis, the easier it will be to achieve better results in this field.”