BIOLOGICAL RESPONSES OF 2 SOYBEAN CULTIVARS EXPOSED TO ENHANCED UVB RADIATION

A UVB exposure and monitoring system has been established at the Oak Ridge National Laboratory's Global Climate Change Research Facility. The system consists of a power supply, and data acquisition and exposure equipment to accomplish controlled, elevated exposure of terrestrial plants to UVB. Plant biomass, selected compounds that absorb UV. radiation, and DNA integrity/damage were measured for two soybean cultivars [Glycine max (L.) Merr.] Forrest and Essex exposed to elevated UVB (32%) above ambient) in this system. The biomass of each major plant organ was observed to be less in soybean cultivar Forrest upon exposure to enhanced UVB with the greatest response in seed pods and stems. In contrast, soybean cultivar Essex showed no biomass response to elevated UVB. Enhanced UVB caused significant (P < 0.1) changes in concentrations of UV-absorbing compounds in both soybean cultivars. The Essex cultivar had an increase in UV-absorbing compounds, whereas a decline was observed for soybean Forrest. There was a decrease in the integrity of DNA, as measured by strand breaks, from both cultivars at 30 and 52 days of exposure. DNA pyrimidine dimers in isolated plant DNA were measured with Micrococcus luteus UV endonuclease. DNA from soybean Forrest exposed to UVB and sampled at 30 and 52 days of exposure had significantly greater (P < 0.05) pyrimidine dimer concentration (dimer frequency approximately 1 dimer per 28,000 DNA bases) than either cultivar exposed to UV treatment for 1 day or Essex at days 30-52 (dimer frequencies less-than-or-equal-to 1 per 120,000 bases of DNA). Decrease in DNA integrity and biomass production in Forrest under elevated UVB may be related to the inability to maintain high concentrations of UV-absorbing compounds in leaves. The tolerant cultivar Essex increased the concentration of UV-absorbing compounds while maintaining biomass production and DNA integrity under elevated UVB.