PARENT SESSION
Contributed Oral Session 49: Climate and Vegetation Dynamics
Tuesday, August 9, 8:00 AM - 11:30 AM, Meeting Room 520 C, Level 5, Palais des congrès de Montréal
Partitioning the effects of UV-A and UV-B in the Development of UV-B screening compounds in soybean Glycine max, under field conditions.
Sullivan, Joe*,1, Xu, Chenping1, Natarajan, Savithiry2, 1 Department of Natural Resource Sciences and Landscape Architecture, College Park, MD, USA2 Soybean Genetics and Improvement Laboratory, Beltsville, MD, USA
ABSTRACT- The induction of UV-B screening compounds in response to UV-B radiation is a commonly reported response in plants and is generally considered to be an adaptive response to UV-B. However, a number of questions remain to be answered including the importance of qualitative and localization differences among species, indirect consequences of changes in leaf chemistry on ecological processes and the dose response of metabolite accumulation. Also the role that UV-A plays in this response has seldom been studied under field conditions. In this study we utilized UV monitoring data provided on site by the USDA UV-B Monitoring and Research Program to monitor the changes in UV-screening compounds in soybeans under a natural range of UV-B radiation. Soybean cultivars Essex, Clark and Clark-magenta, that produces minimal levels of flavonols, were grown beneath shelters covered with polyester to block most UV-B radiation but transmit UV-A or Teflon which is nearly transparent in the UV range. Plants were harvested at regular intervals for pigment and protein analysis. Daily levels of UV-B varied from <1 to >7 kJ m-2 when weighted with a commonly used action spectrum. Increases in UV-screening compounds showed a positive dose response to UV-B radiation in all cultivars with Essex showing the steepest dose response but UV-B levels alone only explained about 50% of the response. The inclusion of UV-A as a treatment factor by using a new action spectrum that includes UV-A and by the use of UV-A alone as a single factor significantly improved the relationship between screening compounds and UV levels and indicated that UV-B levels alone only accounted for about 20% of the total change in screening compounds. Finally, the changes in screening compounds appeared to saturate when cumulative UV-B levels were considered up to a 12-day period and this was most apparent in the magenta isoline of Clark, which suggests that induction of non-flavonoid screening compounds may saturate at lower UV levels than do flavonoids. These results suggest that studies that attempt to assess the role that UV-B may have on protection by inducible screening compound or the ecological implications of changes in leaf secondary chemistry due to increases in UV-B should include UV-A, which is not expected to change with ozone depletion, in the assessment.
Key words: UV-B radiation, action spectra, UV-screening compounds, flavonoids