Scientists Hacked Photosynthesis In Search Of More Productive Crops

Dan Charles wrote . . . . . . . . .

There’s a big molecule, a protein, inside the leaves of most plants. It’s called Rubisco, which is short for an actual chemical name that’s very long and hard to remember.

Amanda Cavanagh, a biologist and post-doctoral researcher at the University of Illinois, calls herself a big fan of Rubisco. “It’s probably the most abundant protein in the world,” she says. It’s also super-important.

Rubisco has one job. It picks up carbon dioxide from the air, and it uses the carbon to make sugar molecules. It gets the energy to do this from the sun. This is photosynthesis, the process by which plants use sunlight to make food, a foundation of life on Earth. Yay for Rubisco!

“But it has what we like to call one fatal flaw,” Cavanagh continues. Unfortunately, Rubisco isn’t picky enough about what it grabs from the air. It also picks up oxygen. “When it does that, it makes a toxic compound, so the plant has to detoxify it.”

Plants have a whole complicated chemical assembly line to carry out this detoxification, and the process uses up a lot of energy. This means the plant has less energy for making leaves, or food for us. (There is a family of plants, including corn and sugar cane, that developed another type of workaround for Rubisco, and those plants are much more productive.)

Cavanagh and her colleagues in a research program called Realizing Increased Photosynthetic Efficiency (RIPE), which is based at the University of Illinois, have spent the last five years trying to fix Rubisco’s problem. “We’re sort of hacking photosynthesis,” she says.

They experimented with tobacco plants, just because tobacco is easy to work with. They inserted some new genes into these plants, which shut down the existing detoxification assembly line and set up a new one that’s way more efficient. And they created super tobacco plants. “They grew faster, and they grew up to 40 percent bigger” than normal tobacco plants, Cavanagh says. These measurements were done both in greenhouses and open-air field plots.

The scientists now are trying to do the same thing with plants that people actually rely on for food, like tomatoes and soybeans. They also working with cowpeas, or black-eyed peas, “because it’s a staple food crop for a lot of farmers in sub-Saharan Africa, which is where our funders are interested in making the biggest impact,” Cavanagh says.

The funders of this project include the U.S. Department of Agriculture and the Bill and Melinda Gates Foundation. (Disclosure: The Gates Foundation also funds NPR.) The USDA has applied for a patent on plants that are engineered in this way.

Cavanagh and her colleagues published their work this week in the journal Science. Maureen Hanson, who is carrying out similar research on photosynthesis at Cornell University, was impressed.

“This is a very important finding,” she says. “It’s really the first major breakthrough showing that one can indeed engineer photosynthesis and achieve a major increase in crop productivity.”

It will be many years, though, before any farmers plant crops with this new version of photosynthesis. Researchers will have to find out whether it means that a food crop like soybeans actually produces more beans — or just more stalks and leaves.

Then they’ll need to convince government regulators and consumers that the crops are safe to grow and eat.

Source: npr

Wild Plants Found in China Sweeter than Sucrose by At Least 25 Times

Two types of plants in Yunnan, Myriopteron extensum and Derris eriocarpa have been found to contain highly sweet-tasting compounds that are at least 25 times sweeter than sucrose, according to researchers from the Kunming Institute of Botany, Chinese Academy of Sciences.

For instance, 12 new sweet-tasting compounds, known as C21 pregnane glycosides, were found in the roots of Myriopteron extensum, a plant commonly used by the Yao minority as food and medicine.

Out of the 12 compounds, nine are highly sweet-tasting compounds which are 25 to 400 times sweeter than sucrose. As compared to the pericarps, the types of sweet-tasting compounds found in the roots were different.

Besides the roots, researchers had previously studied the pericarps of the plant and found it contained 10 new types of sweet-tasting compounds that were 50 to 400 times sweeter than sucrose.

Commenting on the study of the roots, the researchers said that “the quantitation of the sweet compounds in the pericarps, stems, and roots indicated that all of them contain these kinds of sweet components with a distinct distribution.”

Analysis also indicated that the concentrations of these sweet components in the pericarps are higher than those in the stems and roots.

As for Derris eriocarpa, a plant which the Bourau and Dai minorities believe to exhibit medicinal properties, was found to contain four sweet-tasting compounds (triterpenoid saponins).

Two of these compounds were 150 and 80 times sweeter than sucrose.

This is the first scientific study that investigates the sweetening properties of the two plants.

The researchers added that the study helps “provide a theoretical basis for the rational design and development of natural high-potency and non-sugar sweeteners.”

At present, monk fruit and Stevia rebaudiana are some examples of natural sweeteners available in the market.

Israel firm Amai Proteins has also developed computerised ‘designer’ sweet proteins that mimic those that exist naturally in fruits as a sugar alternative. The sweet proteins are hundreds to a thousand times sweeter than sugar.

Methods

After the sweet-tasting components in the plants were identified via phytochemical study and spectroscopic technologies, human sensory evaluation was conducted to determine the level of sweetness of the compounds.

As such, a taste panel was formed using the Givaudan’s panelist selection procedure (taste intensity ranking test).

Common uses

According to the researchers, the two plants are consumed by minorities in Yunnan as both fruit and medicine.

For Myriopteron extensum, its fruit is usually marinated and consumed as salted vegetable, while its roots have medicinal properties, such as reducing inflammation, promoting respiratory tract health and even treating tuberculosis.

On the other hand, Derris eriocarpa is mostly consumed as a drug and reduces phlegm and water retention, and promotes blood circulation.

Source: Chinese Academy of Sciences

As Carbon Dioxide Levels Rise, Major Crops Are Losing Nutrients

Merrit Kennedy wrote . . . . . . .

Plants need carbon dioxide to live, but its effects on them are complicated.

As the level of carbon dioxide in the air continues to rise because of human activity, scientists are trying to pin down how the plants we eat are being affected.

Mounting evidence suggests that many key plants lose nutritional value at higher CO2 levels, and scientists are running experiments all over the world to try to tease out the effects.

Rows of controlled chambers that look kind of like industrial refrigerators are testing how plants react to different levels of CO2 at the U.S. Department of Agriculture’s Adaptive Cropping Systems Laboratory outside of Washington, D.C.

On a recent afternoon, Lewis Ziska, who’s a plant physiologist with the U.S. Department of Agriculture, demonstrates an experiment there with a crop important to many of us — coffee.

The chamber is really bright to mimic the sun. A few neat rows of green coffee plants are growing. The air that they’re absorbing has about the same amount of CO2 as in the preindustrial age, about 250 years ago.

Across the hall, we can see a possible glimpse of the plant’s future. Here, there’s a chamber with plants growing at CO2 levels projected for the end of this century.

“Some of the varieties, you ought to see that they’re bigger,” says Ziska. They’ve all been growing for the same amount of time, but the high CO2 coffee plants are larger. The extra CO2 seems to be making them grow faster.

Scientists have noticed that in many kinds of plants, higher CO2 produces bigger crops. That sounds like a good thing.

But there’s a problem. Bigger doesn’t necessarily mean better. And while they’re still testing what this means for coffee’s quality, scientists have seen that other crops have lost some of their nutritional value under higher CO2 conditions.

One example is rice, a primary food source for more than 2 billion people.

Ziska recently teamed up with an international group of scientists to study whether high CO2 had an effect on the rice’s nutrition. “Was it changing not just how the plant grew, but the quality of the plant?” he asked.

They tested how 18 different kinds of rice responded to CO2 levels that are projected by the end of the century, based on conservative estimates, Ziska says.

The technique they used, called free-air CO2 enrichment, allowed them to grow the rice and add CO2 to the air immediately surrounding the plants using a big hoop in the middle of a field, Ziska explains. They did this over multiple years in facilities in Japan and China.

And the effect was clear: Higher CO2 reduced multiple key measures of rice’s nutritional value. Across the different types of rice, they observed average decreases of 10 percent in protein, 8 percent in iron and 5 percent in zinc. Four important B vitamins decreased between 13 and 30 percent. The research was recently published in Science Advances.

Higher carbon dioxide is not just affecting rice. There’s evidence that the scope of this is much bigger. Harvard’s Sam Myers, who studies the impact of climate change on nutrition, has tested CO2’s impact on the protein, iron and zinc of a number of staple crops using the same free-air CO2 enrichment technique.

“Most of the food crops that we consume showed these nutrient reductions,” Myers says.

The effects varied somewhat — he says wheat showed declines in protein, iron and zinc, and soybeans and field peas showed declines in iron and zinc. Maize and sorghum were less affected.

These studies are enough to raise concerns about the impact on human health, he says.

“Under what circumstances would this be a big problem?” Most likely, he says, it would be in situations where someone is “living relatively near a threshold of nutrient insufficiencies, so you’re just barely getting enough of that particular nutrient.” And secondly, it would more harmful when that person gets a meaningful amount of a nutrient from the crop that’s losing nutritional value.

“There’s quite high global vulnerability to these effects, and we’re likely to see really significant health impacts from these nutrient changes,” he adds.

At the same time, the exact health effects of this are still unclear, says Naomi Fukagawa, the director of the USDA’s Beltsville Human Nutrition Research Center, who was part of the team researching rice. She says it’s hard to know how a person’s health will be affected by changes to the nutritional quality of a specific food in a mixed diet. “We don’t quite have all the answers yet,” she says.

But if this is indeed found to negatively impact people’s health, she says, “what we need to then know, is what else do we have that’s part of their diet that’s culturally sensitive that can make up for those differences?”

Scientists also don’t understand what it is about higher CO2 that causes plants to become less nutritious, Ziska says, though they have some theories.

“We don’t have one simple explanation as to what might be happening,” he says. One possibility is that it could be a simple dilution effect – “as the plants grow more, they become carbon-rich but nutrient-poor.”

However, Myers notes that if this were the cause, all of the nutrients would be decreasing at approximately the same rate. And that’s not necessarily the case. For example, with the recent rice study, most of the minerals and vitamins tested went down, but vitamin E went up.

Another theory, Ziska says, is that the rising carbon dioxide levels change how water moves through the plant, which could also affect some of the nutrients.

“There’s a lot about this that we don’t understand yet,” he says. “And the need to understand this in terms of the potential implications for food quality, and of course for human health, are imperative.”

Source: npr