Solar UV radiation is a source of information for plants

In biological studies UV radiation has most often been connected with the danger it causes to living organisms. Nowadays scientists acknowledge UV radiation's role as a regulator as well. Pioneering studies, conducted in co-operation between the University of Helsinki and Finnish Meteorological Institute, have shown that plants are able to take advantage of complex radiation signals in their growth.

The collaboration that started in 2005 stems from the need to understand biological processes, on one hand, and radiation conditions and the state of the atmosphere, on the other. Not only UV but also other parts of the solar spectral radiation play important ecological roles. Therefore, this kind of biological studies strongly depend on the availability of good measured and simulated information on the prevailing solar radiation conditions.

Only very few biologists have the capability for acquiring on-site quality-assured UV data for their experiments. A method developed at FMI uses radiative transfer calculations together with available information on the state of the atmosphere (for instance, ozone column and clouds) to reconstruct the solar radiation spectrum reaching earth's surface.

A recent study examined the effects of UV radiation and the visible region of the solar spectrum on stimulation of ﬂavonoid biosynthesis in pea plants. Plants synthesize phenolic compounds in response to certain environmental signals or stresses. One group of phenolics, flavonoids, are particularly responsive to UV radiation.

It was demonstrated that solar blue light stimulates ﬂavonoid biosynthesis in the absence of UV-A and UV-B radiation, and it was concluded that pea plants can regulate accumulation of ﬂavonoids by perceiving complex radiation signals that extend throughout the solar spectrum. There is potential to apply this knowledge in horticulture, for instance, where shorter wavelengths of radiation are utilised to induce production of certain phenolic compounds (anthocyanins) in red lettuce.

Future experiments of FMI and University of Helsinki will include a study on the connection of UV-B exposure of plants and their drought tolerance. The experiments will help to find out if it is theoretically possible to forecast future soil drying from UV exposure. Researchers will study long time series of environmental data and examine if plant physiological responses to UV radiation coincide with drought.

To date, the plant biology-radiation collaboration between FMI and the University of Helsinki has resulted in 9 joint publications in refereed journals, two PhD theses, and a handbook on UV research methods. Over the years, the research has been supported by Academy of Finland, Societas Biologica Fennica Vanamo, Societas pro Fauna et Flora Fennica, Finnish Cultural Foundation, LignoCell (project funded by TEKES and the Academy of Finland) and by Maj and Tor Nessling foundation.

Further information

University lecturer and principal investigator Pedro J. Aphalo, Department of Biosciences, University of Helsinki, tel. 0294157897, pedro.aphalo@helsinki.fi, http://blogs.helsinki.fi/senpep-blog/

Senior scientist Anders Lindfors, Finnish Meteorological Institute, tel. 0295392112, firstname.lastname@fmi.fi

Recent publications:

Siipola, S.M., Kotilainen, T., Sipari, N., Morales, L.O., Lindfors, A.V., Robson, T.M., and Aphalo, P.J.: _Epidermal UV-A absorbance and whole-leaf flavonoid composition in pea respond more to solar blue light than to solar UV radiatio_n. Plant, Cell & Env., 2015: 38, 941-952, DOI: 10.1111/pce.12403. http://onlinelibrary.wiley.com/doi/10.1111/pce.12341/abstract

Other peer-reviewed articles:

Morales, L.O., Brosché, M., Vainonen, J.P., Sipari, N., Lindfors, A.V., Strid, Å., and Aphalo, P.J.: Are solar UV-B- and UV-A-dependent gene expression and metabolite accumulation in Arabidopsis mediated by the stress response regulator radical-induced cell death1? Plant, Cell & Env., 2015: 38, 878-851, DOI: 10.1111/pce.12341.http://onlinelibrary.wiley.com/doi/10.1111/pce.12403/abstract

Luis O. Morales, Mikael Brosche, Julia Vainonen, Gareth I. Jenkins, Jason J. Wargent, Nina Sipari, Ake Strid, Anders V. Lindfors, Riitta Tegelberg, and Pedro J. Aphalo. Multiple Roles for UV RESISTANCE LOCUS8 in Regulating Gene Expression and Metabolite Accumulation in Arabidopsis under Solar Ultraviolet Radiation. PLANT PHYSIOLOGY, 161(2):744–759, FEB 2013. DOI: 10.1104/pp.112.211375 http://www.ncbi.nlm.nih.gov/pubmed/23250626

Luis O. Morales, Riitta Tegelberg, Mikael Brosche, Anders Lindfors, Sari Siipola, and Pedro J. Aphalo. Temporal variation in epidermal flavonoids due to altered solar UV radiation is moderated by the leaf position in Betula pendula. Physiologia Plantarum, 143:261–270, 2011. DOI: 10.1111/j.1399-3054.2011.01511.x http://www.ncbi.nlm.nih.gov/pubmed/21883252

Titta Kotilainen, Anders Lindfors, Riitta Tegelberg, and Pedro J. Aphalo. How Realistically Does Outdoor UV-B Supplementation with Lamps Reflect Ozone Depletion: An Assessment of Enhancement Errors. Photochemistry and Photobiology, 87(1):174–183, 2011. DOI: 10.1111/j.1751-1097.2010.00843.x http://www.ncbi.nlm.nih.gov/pubmed/21091954

Titta Kotilainen, Riitta Tegelberg, Riitta Julkunen-Tiitto, Anders Lindfors, Robert B. O'Hara, and Pedro J. Aphalo. _Seasonal fluctuations in leaf phenolic composition under UV manipulations reflect contrasting strategies of alder and birch tree_s. Physologia Plantarum, 140(3):297–309, Nov 2010. DOI: 10.1111/j.1399-3054.2010.01398.x http://www.ncbi.nlm.nih.gov/pubmed/20626643

Luis O. Morales, Riitta Tegelberg, Mikael Brosche, Markku Keinanen, Anders Lindfors, and Pedro J. Aphalo. Effects of solar UV-A and UV-B radiation on gene expression and phenolic accumulation in Betula pendula leaves. Tree Physiology, 30(7):923–934, JUL 2010. DOI: 10.1093/treephys/tpq051 http://www.ncbi.nlm.nih.gov/pubmed/20519675

Titta Kotilainen, Tuulia Venalainen, Riitta Tegelberg, Anders Lindfors, Riitta Julkunen-Tiitto, Sirkka Sutinen, Robert B. O'Hara, and Pedro J. Aphalo. Assessment of UV Biological Spectral Weighting Functions for Phenolic Metabolites and Growth Responses in Silver Birch Seedlings. Photochemistry and Photobiology, 85(6):1346–1355, NOV-DEC 2009. DOI: 10.1111/j.1751-1097.2009.00597.x http://www.ncbi.nlm.nih.gov/pubmed/19682323

Titta Kotilainen, Riitta Tegelberg, Riitta Julkunen-Tiitto, Anders Lindfors, and Pedro J. Aphalo. Metabolite specific effects of solar UV-A and UV-B on alder and birch leaf phenolics. Global Change Biology, 14(6):1294–1304, JUN 2008. DOI: 10.1111/j.1365-2486.2008.01569.x http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2486.2008.01569.x/abstract