Plants produce their own beneficial “sunscreens” in response to UV-B. Supplying UV-B to greenhouse food crops can alter growth, increase nutritional value, and enhance flavor.

By Michael Dzakovich

It’s finally that time of year. The days are getting cooler and your local grocery store is putting out pumpkins for Halloween. While the need to apply a new coat of sunscreen every few hours seems like a distant memory, plants are continuing to respond to ultraviolet B (UV-B) radiation by making their own sunscreen. But unlike the sunscreens we use, plants make special compounds called flavonoids and carotenoids to help absorb UV-B radiation. Coincidentally, many of these compounds might also be good for our health (Spencer, 2009; Story et al., 2010).

UV-B makes up less than 2% of the total amount of light that reaches the earth, but can have a big impact on the way a plant grows and develops. For example, UV-B can influence a plant’s height, how “bushy” it is, how the plant responds to pests and diseases, how it photosynthesizes, the color of its leaves and flowers, and many other things (Aphalo et al., 2012; Wargent and Jordan, 2013). Like other forms of light, UV-B is perceived by a photoreceptor. But unlike other forms of light, UV-B can also be perceived by DNA damage when there is too much UV-B for the plant to handle (Gardner et al., 2009).

A few years ago, it was discovered that ULTRAVIOLET RESISTANCE LOCUS 8 (UVR8) is the photoreceptor responsible for perceiving UV-B radiation (Rizzini et al., 2011). This complex is made up of two identical proteins that split apart in the presence of UV-B radiation. Then, the pieces are sent into the nucleus of cells where they interact with other proteins that are important for the perception of many colors of light such as far-red, red, and blue. The overlap between the ways that different colors of light are perceived by plants creates competition for these proteins. If growers want to leverage the effects of UV-B radiation, it is important to keep this balance in mind. Even small amounts of UV-B radiation added into a background of visible light could alter the characteristics of a crop or ornamental plant.

But how can growers use UV-B radiation to their benefit? For one thing, UV-B radiation is not present in greenhouses because glass and some plastics block the transmission of UV-B. Crops grown in these environments may not have the same quality as their field-grown counterparts. With the advent of light emitting diodes (LEDs), new fixtures could be custom-built to include a little bit of UV-B radiation along with other colors of light. This could be used by growers to force crops into making more sunscreens (flavonoids and carotenoids) and these crops could be sold at a premium due to their potentially increased health properties. An example of lettuce grown with and without UV-B radiation can be seen in figure 1.

MD UV light and lettuce
Figure 1. The same variety of lettuce (‘Cherokee Purple’) grown with (L) and without (R) UV-B radiation. Those grown without UV-B radiation (R) had large, pale leaves while those grown with UV-B (L) formed compact plants with high concentrations of carotenoids and flavonoids.

Another application could be to alter the flavor of crops. The compounds that create flavors come from the same pathways as flavonoids and carotenoids, so UV-B might be important in the development of flavor in a variety of crops like herbs (Johnson et al., 1999) and even vegetables like tomatoes. A recent study that I conducted showed that ultraviolet radiation can slightly improve the flavor of greenhouse tomatoes (Dzakovich et al., 2016). Of course, how UV-B can be used to reprogram crops is a new area of research and is not well understood. Growers would need to take precautions to avoid any negative effects of UV-B by wearing protective eye wear and covering their skin. With a little more research, UV-B might just become the next big topic in controlled environment agriculture.

Works Cited

Aphalo, P.J., Albert, A., Mcleod, A.R., Robson, T.M., and Rosenqvist, E. (2012). Beyond the Visible (COST Action FA0906 UV4growth).

Dzakovich, M.P., Ferruzzi, M.G., and Mitchell, C.A. (2016). Manipulating Sensory and Phytochemical Profiles of Greenhouse Tomatoes Using Environmentally Relevant Doses of Ultraviolet Radiation. J. Agric. Food Chem. acs.jafc.6b02983.

Gardner, G., Lin, C., Tobin, E.M., Loehrer, H., and Brinkman, D. (2009). Photobiological properties of the inhibition of etiolated Arabidopsis seedling growth by ultraviolet-B irradiation. Plant, Cell Environ. 32, 1573–1583.

Johnson, C.B., Kirby, J., Naxakis, G., and Pearson, S. (1999). Substantial UV-B-mediated induction of essential oils in sweet basil (Ocimum basilicum L.). Phytochemistry 51, 507–510.

Rizzini, L., Favory, J.-J., Cloix, C., Faggionato, D., O’Hara, A., Kaiserli, E., Baumeister, R., Schäfer, E., Nagy, F., Jenkins, G.I., et al. (2011). Perception of UV-B by the Arabidopsis UVR8 protein. Science 332, 103–106.

Spencer, J.P.E. (2009). Flavonoids and brain health: multiple effects underpinned by common mechanisms. Genes Nutr. 4, 243–250.

Story, E.N., Kopec, R.E., Schwartz, S.J., and Harris, G.K. (2010). An update on the health effects of tomato lycopene. Annu. Rev. Food Sci. Technol. 1, 189–210.

Wargent, J.J., and Jordan, B.R. (2013). From ozone depletion to agriculture: understanding the role of UV radiation in sustainable crop production. New Phytol. 197, 1058–1076.

Ultraviolet B: invisible light with a visible impact
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