Controlling Plants with Light: LEDs to Change Plant Growth

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Cryptochromes are a class of blue light-sensitive pigments found in plants and animals. Image by Brautigam, C.A., Smith, B.S., Ma, Z., Palnitkar, M., Tomchick, D.R., Machius, M., Deisenhofer, J.

This is the basis behind Folta’s research. By using different parts of the spectrum, we give a plant inputs or instructions that result in predictable biochemical events to lead to tangible outcomes that can be controlled. In a way, the plant becomes a machine or hardware and light becomes the software in which we can program this machine.

Creating the One Plant Salad

Chefs are constantly looking for ways to combine colors, flavors and textures in the foods they cook. Folta showed the audience some examples, using the same type of lettuce, where they have achieved changes in texture and coloration. Researchers grew lettuce using red light to show hints of purples while the same plant under predominantly blue light showed a stronger response in purple coloration.

This means rather than diversifying or growing five types of lettuce, a small farmer can grow one type of lettuce and change the color his plants receive to create lettuces with different flavors, colors and textures. The resulting changes in coloration and texture have been used to create the one lettuce salad, something which Folta showed the audience. While they haven’t yet produced lettuce with different flavors, Folta believes this should not be difficult using this process.

Improving Nutrition and Taste by Using Light

Folta also says that this process can improve the nutritional value of plants. Work with red russian kale shows a tremendous increase in the level of antioxidants by modulating the level of red pigments found in the plant. Thus by not adding chemicals or changing genetics, we can use light to get plants to give us what we need.

The above circuit shows the movement of charge carriers. Electrons combine with holes to release energy in the form of photons. Image by S-kei

Light therapy can even make fruit taste better after it has been picked and Folta imagines refrigerators with special light compartments to ripen fruits and vegetables. This can also give plants a longer shelf life by using light to modulate the plant’s metabolism. The same type of instructions can also be sent to flowers and florists may one day place LEDs in their bouquets to prolong life and change when and how flowers release scents.

How Do LEDs Work?

Though the knowledge of using light to control plants is not new, it has only become practical with advances in LED technology. LEDs are made up of semiconducting materials doped with impurities to create a p-n junction, the interface or boundary where two types of semiconductor exist in a single crystal.

Each material contains a different type of charge carrier-the p-type material contains “holes” or the absence of electrons and the n-type material contains an abundance of electrons. When a potential is applied across an LED’s junction, charge carriers move and combine at the junction to release energy in the form of a photon.The wavelength of the light the LED emits (and thus its color) depends on the material’s bandgap. This means that the color of light is highly monochromatic – or it emits only one color.

As a LED’s color depends on the choice of semiconducting materials, it means that these devices can be specially tuned to interact with the various plant receptors to get a response. We can, for example, either design or buy off the shelf red LEDs that can interact with the phytochrome molecule directly. Previously this was unfeasible as LEDs were expensive and produced very little light – but today, not only are LEDs cheap, and getting more so, but recent advances have also seen an increase in light output.

This ability to produce a lot of light at low cost makes LEDs the ideal device to control and communicate with plants.

During the final Q&A session, attendees asked Folta whether this technology could produce allergen-free plants and fruits. While that is presently not a focus of his research, he says could be possible to do so. As the allergens typically found in foods are specific proteins to which the body reacts, they may be able to switch off expression of certain genes so that the plant doesn’t produce the allergenic proteins.

According to Folta, this research is of tremendous interest to companies who are seeking to maximize the genetic potential of their crops without the need for chemicals or genetic modification. As many types of crops and growing spaces are amendable to this treatment, there is the potential to convert almost any space to grow crops both efficiently and cheaply and thereby reduce environmental impact.

LEDs and the Language of Plants

This becomes more and more important in a world with a growing global population that is increasingly seeing arable land growing more and more scarce. By understanding the language of plants, we may one day write the software needed to efficiently grow cheap and nutritious food for a growing world anywhere.

Resources

Science Writers 2013. Welcome. (2013). Accessed November 12, 2013.

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