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Sun on the plant and in the tank

Workshop organized by Bioen brings together specialists that study the use of photosynthesis as a source of energy

miguel boyayanThe increase of carbon gas (CO2) in the air, a consequence of global climate change, has increased the efficiency of sugar cane to transform solar energy into biomass. These results were presented by biologist Marcos Buckeridge, from the University of São Paulo/USP, at the Bioen/PPP Ethanol and Sugarcane Photosynthesis workshop. The workshop was held at FAPESP on February 18 as part of the FAPESP Bioenergy Research Program/Bioen, which fosters scientific investigation related to the search for more efficient energy-producing materials based on biological processes.  The event was attended by Swedish and Brazilian researchers who discussed the search for clean energy sources and ways to set up scientific partnerships. In addition to using sugar cane as a biological reactor, the Swedish researchers from Uppsala University have been investigating forms to reproduce photosynthesis reactions without the help of plants, as reported by biochemist Stenbjörn Styring.

The idea to organize the workshop came from agricultural engineer Luis Augusto Cortez, from the State University of Campinas/Unicamp. According to Cortez, the production of sugar cane accounts for 70% of the total cost of ethanol ? hence the urgency to improve productivity. “From 2005 to 2025, it will be possible to nearly double the productivity solely with technological improvements related to cultivation and to plants”, he said. Ironically, global climate change can help in this search, as shown in the work conducted by Buckeridge and doctorate student Amanda Pereira de Souza. “We wanted to find ways of dealing with the increase of CO2 in the atmosphere and we discovered that sugar cane takes advantage of this increase”, he says.

Buckeridge and Amanda reached these conclusions by cultivating sugar cane inside transparent chambers where they could manipulate carbon gas concentration and compare the results with plants that grow in the normal environment with double the amount of CO2. The results of the study, published in the Plant, Cell and Environment journal, show that plants growing for 50 weeks in a carbon gas-intensive environment produced, on average, 30%  more photosynthesis, grew 17% taller, used water more efficiently, and gained 40% more total biomass, which includes stems, roots and leaves. This increase is precious for the production of cellulosic ethanol, which is obtained from the cell walls of plants; cellulosic ethanol is one of the ways of getting more benefits from using sugar cane as fuel.

To understand the transformations that have led sugar cane to be more productive, the two biologists set up a partnership with Glaucia Souza, from the University of São Paulo’s Chemistry Institute. Together, the three researchers studied the genetic activity of the plants cultivated under the two conditions and discovered differences in the expressions of 36 genes: 14 were repressed and 22 were more active in plants that had been exposed to more CO2. Four of these genes are known to be related to photosynthesis, most of them with the transportation of electrons, an important step in the chemical reactions of this biological process which is the base of life on our planet. In 2008, Buckeridge and Amanda repeated the experiment in carbon gas chambers and verified that the transportation of electrons is actually 43.5% more efficient under high concentrations of carbon gas. As the second phase of the experiment was conducted at a time when temperatures were higher, the results were even more outstanding: photosynthesis increased by 60%, which resulted in 60% more biomass than in the plants cultivated under normal circumstances.

To guide the increase in productivity even if global climate changes are reverted and the air does not undergo the changes that have been predicted so far, the researchers still need to understand exactly how the carbon gas acts to increase the efficiency of photosynthesis in terms of capturing light, a task which the event organized by FAPESP may have helped. While his colleague Fikret Mamedov was describing photosynthesis in details, Styring was telling Buckeridge which proteins might have been responsible for his findings. “He showed me things that I had never thought of before”, said the USP researcher.

Fueled by the sun
Styring explained that researchers have to be bold to deal with the energy crisis threat. In his opinion, merely improving existing energy producing technologies, such as fuel burning, will not save the planet. He considers currently used solar panels as being primitive, inefficient – and simply modifying them will not result in any substantial increase of the energy currently being produced by this method. “It is necessary to produce hydrogen for fuel directly from sunlight” he said. According to the Swedish biochemist, a lot of energy is lost when plants are used to transform sunlight into fuel. In his opinion, the solution lies in artificial photosynthesis:  this can be done by developing bioreactors that imitate the essential steps of the reactions that take place inside the plants to produce energy. The Swedish researcher believes this is possible, but he does not know when and how much it would cost.

The first problem is to select what to copy, as photosynthesis includes a complex series of reactions. “When the Greeks wanted to learn how to fly, they watched the birds”, he compared. After much experimenting, the Greeks discovered that wings were actually useful, but the other characteristics of birds were not that useful.  “Airplanes don’t lay eggs and people who tried to fly by moving wings died”, he joked. It is necessary to discover what is important in photosynthesis – hence the need to become familiar with all the details of this process.

Mamedov reported that the group from the University of Uppsala has the means to unveil these details, and have already done so. Now they are experimenting with what Styring calls chemical Lego, referring to the toys made in Denmark, Sweden’s neighboring country; the researchers assemble groups of molecules to produce a biological reactor. To this end, Styring’s team links natural enzymes to atoms of manganese, iron and ruthenium, for example. He has already been able to develop a complex that can generate energy, but the researcher is not announcing any victory. “The artificial systems are a conceptually new and original solution, with a lot of potential, but there is no way of knowing when we will achieve any breakthrough”, he said.

Meanwhile, Buckeridge celebrates the seeds sown by the meeting: Mamedov is expected to come to São Paulo this year to isolate sugar cane chloroplasts, where photosynthesis occurs, and then study the data in Sweden, to broaden the knowledge on how these plants capture light.  In addition, two students in the master’s program are scheduled to go to Sweden to study how light is captured by two plant species from the Amazon Region.

Scientific Article
SOUZA, A.P. et al. Elevated CO2 increases photosynthesis, biomass and productivity, and modifies gene expression in sugarcane. Plant, Cell and Environment. v. 31, n. 8, p. 1.116-1.127. ago 2008.