by Wynne Parry

The thick, often curly leaves of kale pack a nutritional punch that has made this vegetable a darling among health-food enthusiasts. Now, some scientists want to make it even better for you.

University of Florida researchers say they can alter the levels of antioxidants and other healthy compounds in sprouts, including kale. They are employing a technology found everywhere from traffic signals to computer power buttons: light-emitting diodes (LEDs).

LEDs are small, cool and energy efficient. They also produce light from narrow bands within the spectrum, making it easy to give plants a focused dose of, say, red light. This functionality is important because scientists have known for some time that a plant’s chemical processes can alter depending on the wavelength of light to which it is exposed. Studies have shown sweeping metabolic changes occur in plants when they are grown under different qualities of the light, including some humans cannot see.

The University of Florida team, led by plant biologist Kevin Folta, hopes to devise LED-driven prescriptions for crops growing in greenhouses, kitchens or even off the planet. Folta wants to harness these changes. “We are taking that basic fundamental research and then translating it to crops that matter,” Folta says. Perhaps one day, “every single plant will have a set of rules for light that will allow you to maximize the presence of the compounds you want.”

LEDs and the future of crops

LEDs can output different bands of wavelengths depending on the type of semiconductor material an electrical current passes through inside the light. These bands can correspond to particular colors, such as red or blue light, or they may fall outside the part of the spectrum visible to human eyes, as is the case with ultraviolet light. Sunlight is quite different, though; it is a mixture of visible and invisible wavelengths of electromagnetic radiation.

The narrow bands of light produced by LEDs suite them to experiments on plants’ response to particular wavelengths. Plant scientists first took advantage of this opportunity more than a decade ago, when they used red LEDs supplemented by blue fluorescent light to grow lettuce.

The price and efficiency of LEDs has improved since they were invented more than 50 years ago, opening up more possibilities for their use growing plants in controlled environments. The technology now offers a number of potential improvements to this type of garden. For instance, energy-efficient LEDs could promote local food by making it feasible for commercial growers to produce out-of-season crops indoors, and NASA is interested in using LEDs to grow food for astronauts in space.

Experiments with LEDs have already shown that blue light can boost levels of health-promoting pigments, anticancer compounds known as glucosinolates, as well as minerals in broccoli sprouts. Building on many studies like this, Sofia Carvalho, a postdoctoral researcher in Folta’s lab, has been trying out red, blue and far-red light on sprouts while varying light sequences, combinations and exposure time. The results of these experiments have yet to be published.

The primary goal is to figure out how to control aspects of a sprout’s nutritional content.

(Sofia Carvalho, a University of Florida postdoctoral researcher, holds lettuce grown under red and blue LEDs. Courtesy Kevin Folta/UF.

Light paints nutritious compounds on plants

Red Russian kale, one of the study’s subjects, appears in markets with purple stems and sometimes leaves. This color is evidence of the plant’s health value; the pigments responsible are anthocyanins. Known to have a variety of beneficial effects, from reducing blood sugar to fighting cancer and inflammation, anthocyanins, are found in other deeply colored fruits and vegetables. These pigments are among the compounds Folta, Carvalho and others are seeking to augment.

Blue is widely recognized as the light that boosts these compounds, and in the kale it can have dramatic effects. A sprout that starts out green and yellow turns a much darker hue after some time under a blue light. “You essentially paint it dark purple with light,” Folta says.

While blue does boost anthocyanins in the kale, the plant appears to have its own quirk: a particular sensitivity to far-red light. Typically, far-red wavelengths tell a plant it is growing in shade, prompting the plant to adjust its internal chemistry. In the case of red Russian kale, experiments have shown far-red can give a potent boost to the plant’s production of anthocyanins and antioxidants. But too much far-red light inhibits plants’ growth.

Far-red wavelengths fall at the edge and outside the spectrum of light visible to people. As a result, the sprouts under far-red can appear to be growing under dim red light, Carvalho says.

Their experiments have focused on another type of healthy compound: glucosinolates. Kale produces these sulfur-containing compounds, which can have anticarcinogenic effects. The light treatments caused shifts in different types of glucosinolates, but these changes aren’t yet well understood.

In related work, Folta and others found light treatments could alter the production of the volatile compounds responsible for flavor and aroma in produce and flowers. Using light to enhance the flavor of a strawberry or boost the nutrition in greens could allow growers to sidestep the controversy surrounding genetically modified organisms. “The beauty of this is we have one set of genes that we are stretching to a wide variety of outcomes,” Folta says.

Top Image: Kevin Folta, a University of Florida plant biologist, uses light from LEDs to tweak the flavor, nutritional content and growth of plants. Courtesy Josh Wickham/UF.

Wynne Parry is a freelance science journalist based in New York City. As a web and print reporter, she has covered dinosaur smuggling, the secret life of RNA and the arrival of invasive species on Antarctica. She contributes to LiveScience.com and Quanta magazine, and her work has appeared in numerous other publications, including The New York Times and New York Post.