Chenping Xu

Coupling short-term changes in ambient UV-B levels with induction of UV-screening compounds.

A substantial number of studies have been conducted over the last several decades to assess the potential impacts of long‐term increases in ultraviolet‐B radiation (UV‐B between 280 and 320 nm) that will result from continued depletion of stratospheric ozone. However, seasonal changes, tropospheric chemistry and cloudiness are the dominant factors controlling ambient UV‐B levels on a short‐term or daily basis. The effects of short‐term changes in UV‐B on plant growth, phytochemistry and physiological processes have received relatively little attention. The USDA UV‐B Monitoring and Research Program provides an excellent network of stations that provide an opportunity to monitor long‐term changes in solar UV‐B radiation and evaluate 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 on separate groups of seedlings planted at intervals over the growing season during contrasting periods of ambient levels of UV radiation. The levels of UV‐screening compounds correlated with UV‐B levels in both species and with UV‐A in soybean but the sensitivity of the response differed between the two species and among the soybean cultivars. Response differences among species may be related to unique secondary chemistry of each species, so one response estimate or action spectrum may not be appropriate for all species.

Utility of proteomics techniques for assessing protein expression

Proteomic technologies are currently used as an effective analytical tool for examining modifications in protein profiles. Understanding the natural variation of soybean seed proteins is necessary to evaluate potential unintended (collateral) effects due to transgenic modifications in genetically modified (GMO) soybeans. We used two-dimensional polyacrylamide gel electrophoresis (2D-PAGE), matrix-assisted laser desorption/ionization time of flight (MALDI-TOF) mass spectrometry, and liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) to separate, identify and quantify the different classes of soybean seed proteins. Sixteen soybean genotypes, including four wild and twelve cultivated genotypes, belonging to four different subgroups were used as models for protein profile evaluation. Significant variations of allergen and anti-nutritional protein profiles were observed between two different groups, cultivated and wild soybean genotypes. However, only minor variations in protein profiles were observed within the soybean samples from the same group (cultivated or wild). These results may be useful to scientists needing to compare GMO and non-GMO soybeans once additional data are generated on additional soybean varieties and the same varieties grown at different geographical locations.

Development of UV-B screening compounds in response to variation in ambient levels of UV-B radiation

The induction of UV-B screening compounds in response to exposure to UV-B radiation is a commonly reported response and is generally considered to be an adaptive response of plants for protection from UVinduced damage. However, a number of questions remain to be answered including the importance of qualitative and localization differences among species in providing protection, indirect consequences of changes in leaf secondary chemistry on ecological processes and the dose response of metabolite accumulation. 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 range of UV-B levels due to natural variation in ambient UV-B radiation. Soybean cultivars Essex, Clark and Clark-magenta, an isoline of Clark that produces minimal levels of flavonols, were grown beneath shelters covered either with polyester to block most UV-B radiation or teflon which is nearly transparent in the UV range and harvested at regular intervals for pigment and protein analysis. Daily levels of weighted UV-B varied from <1 to >7 kJ m-2. Increases in UV-screening compounds showed a positive dose response to UV-B radiation in all cultivars with Essex showing the steepest dose response. UV-A also induced screening compounds in all species The hydroxycinnimates of the magenta isoline showed a steep dose response to UV-A and a rather constant (non dose specific) but small additional increment in response to UV-B. The Clark isoline, which produced primarily the flavonol quercetin, showed a dose response to UV-B intermediate between that of Clark-magenta and Essex. All three cultivars show similar tolerance to UV-B in field conditions indicating that UV-induced pigment production is adequate to protect them from excessive UV-B damage.