Research

Filter by tag:
UVC

Controlling Plants with Light: LEDs to Change Plant Growth

Jul 23, 2015 Posted by: Veronica DeLuca

For much of human history, people have managed plant growth in the same way – take the plant outside, put it in the ground and wait for it to grow. But what if, rather than doing this, we could give a plant managed instructions? In essence we would talk to the plants. Then, not only could we tell plants what to produce and how much to produce but do so by communicating in a language that they can understand.

According to new research, we can get a plant to do exactly what we want by using a vocabulary of commands via light-emitting diodes, or LEDs.

Kevin M. Folta, Interim Chairman and Associate Professor, Horticultural Sciences Department, University of Florida, Gainesville, FL. Image courtesy of the University of Florida.This sounds like science fiction, but it isn’t. At the recent Science Writers 2013 conference in Gainesville, FL, Dr. Kevin M. Folta (pictured, right) of the University of Florida showed us his vision of growing plants in the future. In this world, there will be automatic lighting systems and reflective surfaces that use varying colors of light to fine-tune a plant’s nutrition, flavor, texture and many other attributes.

Photoreceptor chemistry lets researchers manage many aspects of a plant’s life and growth can be. Now that inexpensive Light Emitting Diodes (LEDs) are available in many wavelengths, Folta’s lab has found ways to use light to manipulate gene expression and dynamically improve nutrition and flavor, control pests, time of flowering and ripening and slow spoilage.

Plants as Environmentally Modified Organisms (EMOs)

Folta says that all plants have a certain genetic potential determined by their genetic makeup, and that we can change that genetic potential either by selection or genetic modification. What happens to a plant largely depends on its environment and by manipulating this environment we can reach the potential determined by a plant’s genetic blueprint.

Folta describes plants as Environmentally Modified Organisms that are able to adapt to change or express their genetic potential based on the signals they receive in their environment. Instead of manipulating physical variables, such as spacing between plants, Folta seeks to make photomorphogenesis changes – to induce changes in plant growth, quality, texture and flavor by using light.

This idea works because plants have three receptors that respond to different parts of the spectrum; the phytochrome pigment responds to the red part of the spectrum, cryptochrome responds to green and blue light and photropin which responds to blue light and controls plant growth.

The idea of using different colors of light to control plant growth is not new, but to understand why it works, Folta says we must understand that different adaptions in an organism are the result of different genes being expressed. In much the same way a plant grown in darkness grows long and tall as it tries to find light, the same type of plant will grow differently outside when exposed to light. They are both genetically identical but the genes that control growth are switched on or off in response to light.

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.

LED Circuits

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

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.

 

This article was written by David Latchman and was found at www.decodedscience.org.
© Copyright 2013 David Latchman, All rights Reserved. Written For: Decoded Science

Shining a Light on Circadian Rhythms in Plants

Jul 11, 2015 Posted by: Veronica DeLuca

Preserving the living nature of foods could increase nutritional value. 

We take it for granted that the refrigerator light goes off when we shut the door. But perhaps fridges of the future will be different, as new research suggests exposing fruits and vegetables to light during storage could make them more nutritious.

Plant parts, like leaves and roots, keep living after having been separated from the plants on which they grew. For days, weeks, even months after being harvested, the component cells of these plant parts can carry on with their metabolic functions. That is why you can grow fresh food by upcycling kitchen scraps.

Most any item that hasn’t rotted to the point of inedibility can be considered living. This is one of the selling points of a raw foods diet, as living foods contain enzymes and other molecules that cooking destroys.

A paper published in Current Biology during July of last year indicates that cyclic exposure to light and dark causes fruits and vegetables to regulate their cellular metabolism such that the amounts of certain compounds are increased, some of which are beneficial.

The paper’s researchers, based at Rice University and the University of California at Davis, have published previously on the phenomenon of “entrainment” in plants. Entrainment refers to the programming of an organism’s circadian rhythms into certain routines.

The group had examined how exposure to light influences the ability of Arabidopsis, a plant in the cabbage family, to ward off insect damage. They found that the plant ramps up its levels of natural insecticide chemicals shortly before dawn, when insects begin feeding. In a controlled experiment, the researchers were able to use light/dark cycles to dramatically slow the rate at which caterpillars devoured a leaf.

According to one of the team’s leaders, Dr. Janet Braam of Rice University, one category of insect-discouraging chemical, glucosinolates, is known for anti-cancer properties in human, and she says there might be others.

“We have found that two plant hormones that are critical for plant defense are controlled by the circadian clock, that is, their levels vary depending upon time of day. We hypothesize that these hormones regulate the levels of metabolites important for defense,” Braam said via email.

Her team’s new paper examined the effect of simulated day and night cycles on the internal clocks of blueberries, spinach, lettuce, carrots and squash. All of these exhibited entrainment in response to light.

“It is surprising that carrots responded to the light/dark cycles because they are typically underground and not, therefore, exposed to light,” Braam says. “However, the carrot cells retain structures that are related to chloroplasts [plant cellular structures where photosynthesis takes place] and perhaps in response to light these structures remain light responsive.” 

 

This article was written by Ari LeVaux and found on BoulderWeekly.com

How Exposure to Irregular Light Affects Plant Circadian Rhythms

Jul 08, 2015 Posted by: Veronica DeLuca


Source: American Society for Horticultural Science.

A study of chrysanthemum investigated plants' circadian responses to interruptions in light cycles. Plants were exposed to irregular supplemental light breaks during the night; results showed a correlation between circadian-regulated processes and plant growth. Leaves and stems grew faster in plants grown in short days with irregular light breaks during the night compared with plants grown in a climate with a consecutive long light period. The findings could contribute to energy savings in production greenhouses.

Scientists know that plants can actually "sense" day length, and "schedule" their growth to coincide with specific environmental conditions. These natural events are based on the circadian clock, a 24-hour system found in most biochemical and physiological processes. Plants grow better in circadian conditions that correspond to natural environments, but until now researchers have not understood how plants' internal circadian clocks respond to irregular lighting environments such as those found in many greenhouses.

Greenhouses in northern latitudes rely heavily on supplemental light sources to extend the number of
light hours during the day. To conserve electricity and lower costs, newer low-energy input systems use lights only during less expensive off-peak hours and turn lighting off during peak load periods in the afternoon and in the morning. These systems, though more cost-effective than conventional lighting methods, create irregular lighting patterns of natural sunlight interrupted with artificial lighting -- a challenge for both growers and plants.

Danish scientists Katrine Heinsvig Kjaer and Carl-Otto Ottosen from the Department of Horticulture at
Aarhus University published a study in a recent issue of the Journal of the American Society for Horticultural Science that sheds light on the question of plants' response to interruptions in lighting cycles. "Circadian rhythms are believed to be of great importance to plant growth and performance under fluctuating climate conditions. However, it has not been known how plants with a functioning circadian clock respond to irregular light environments that disturb circadian-regulated parameters related to growth," they explained.

For their experiments, the team used 300 cuttings of chrysanthemum (Chrysanthemum morifolium 'Coral Charm') grown in 19 hours of light for 2 weeks. The plants were then randomly placed in either of two greenhouse compartments with similar temperatures and carbon (CO2) concentration. "The plants were exposed to supplemental light provided as irregular light breaks during the night, which we achieved by controlling the light based on forecasted solar irradiance and electricity prices', explained the authors. "Growth, in terms of carbon gain, was linearly correlated to both day length
and daily light integral."

The scientists observed that chrysanthemum plants grown in short days with irregular light breaks during the night showed more rapid leaf development and stem growth than plants grown in a climate with a consecutive long light period, proving that low average light intensity promotes expansion of the photosynthetic area of the plants. Though the experiments showed that irregular light periods disturb circadian rhythm and induce changes in leaf characteristics, the authors noted that the study also proved that plants can naturally adapt to irregular light periods.

Kjaer and Ottosen say their research should help greenhouse operators realize energy

savings in the area of supplemental light usage.

Story Source:

The above story is based on materials provided by American Society for Horticultural Science.

Journal Reference:
1. Katrine Heinsvig Kjaer And Carl-Otto Ottosen. Growth of Chrysanthemum in Response to Supplemental Light Provided by Irregular Light Breaks during the Night. JASHS, January 2011 vol. 136 no. 1 3-9