Submitted to: Photochemistry and Photobiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/27/2007
Publication Date: 7/23/2007
Citation: Sullivan, D., Gitz, D.C., Liu-Gitz, L., Gao, W., Slusser, J. 2007. Coupling short-term changes in ambient UV-B levels with induction of UV-screening compounds. Photochemistry and Photobiology. 83(4):863-870. Interpretive Summary: Because plants are not capable of moving from one place to another, they simply have to stay in one place and take whatever the environment throws at them. Understanding exactly how plants deal with environmental stresses is a first step in developing crops which tolerate stress. Sunlight contains ultraviolet radiation which has been shown to damage plants. Plants make compounds, secondary phenolics, in their leaves which protect against UV, just as humans accumulate melanin in their skin in response to UV. We investigated how rapidly Barley can adapt to UV in the field. We found that these plants vary the amount of sunscreen pigments more rapidly than was previously thought. This work is also important since UV has been shown to make plants tolerant to other stresses such as drought and cold.
Technical Abstract: A substantial number of studies have been conducted over the last several decades to assess the potential impacts of long-term increases in UV-B radiation (UV-B between 280-320 nm) that might result from continued depletion of stratospheric ozone. However, in addition to stratospheric ozone levels and seasonal changes, tropospheric conditions such as cloudiness exert a much larger influence on short-term fluctuations in ambient UV-B levels. The effects of short-term changes in UV-B radiation on plant growth, phytochemistry and physiological processes have received relatively little attention. The USDA UV-B Monitoring and Research Program provides an excellent opportunity to monitor long-term changes in solar UV-B radiation and the responses of plants to short-term variation in UV-B levels on a near real time basis. In this study Barley (Hordeum vulgare L.) and soybean (Glycine max (L) Merr.) were used as model systems. Emerging seedlings of these species were grown under either near ambient levels of UV-B or under reduced levels (ca 90% reduction) in the field. Periodic measurements of foliar UV-screening compounds were made of separate groups of seedlings planted at intervals over the growing season following contrasting periods of ambient levels of UV-B. Ambient levels of UV-B modulated the levels of flavonoids and other putative UV-screening compounds in both species but the role of UV-A was more pronounced in soybean than in barley. These results suggest that short-term fluctuations in solar UV-B levels may modulate screening compound levels and subsequent protection from UV-B damage at higher UV-B levels. Species-specific differences may be related to the kinetics of the induction of the phenylpropanoid pathway.