Non-structural phenolic compounds perform a variety of functions in plants, including acting as antioxidants. We describe a microplate-adapted colorimetric total phenolics assay that utilizes Folin-Ciocalteu (F-C) reagent. The F-C assay relies on the transfer of electrons in alkaline medium from phenolic compounds to phosphomolybdic/phosphotungstic acid complexes, which are determined spectroscopically at 765 nm. Although the electron transfer reaction is not specific for phenolic compounds, the extraction procedure eliminates approximately 85% of ascorbic acid and other potentially interfering compounds. This assay is performed in microcentrifuge tubes and assessed in a 96-well plate reader. At least 64 samples can be processed in 1 d.

Photosynthetic and respiratory exchanges of CO2 by plants with the atmosphere are significantly larger than anthropogenic CO2 emissions, and these fluxes will change as growing conditions are altered by climate change. Understanding feedbacks in CO2 exchange is important to predicting future atmospheric [CO2] and climate change. At the tissue and plant scale, respiration is a key determinant of growth and yield. Although the stimulation of C 3 photosynthesis by growth at elevated [CO2] can be predicted with confidence, the nature of changes in respiration is less certain. This is largely because the mechanism of the respiratory response is insufficiently understood. Molecular, biochemical and physiological changes in the carbon metabolism of soybean in a free-air CO 2 enrichment experiment were investigated over 2 growing seasons. climate change ͉ elevated CO2 ͉ free air CO2 enrichment ͉ metabolic ͉ soybean T he rate at which atmospheric CO 2 concentration ([CO 2 ]) is rising and driving climate change is the net consequence of anthropogenic carbon emissions plus ecosystem processes that release or remove carbon from the atmosphere. Carbon emission to the atmosphere from fossil fuel burning, cement production and land use change has risen to Ϸ10 PgCy Ϫ1 (1). Dark respiration from plants in terrestrial ecosystems is a much larger flux, emitting 50-60 PgCy Ϫ1 (2). The change in plant respiration that will occur by the middle to end of this century in direct response to rising [CO 2 ] has long been of interest and uncertainty (3, 4). Changes in respiration will combine with the well characterized stimulation of C 3 photosynthesis by elevated [CO 2 ] to impact the net primary productivity of ecosystems and their capacity to act as sources or sinks of carbon. Key synthesis papers have variously concluded that elevated [CO 2 ] will cause plant respiration to increase as much as 11%, decrease as much as 18%, or not change (5-8). This uncertainty corresponds to an increase or decrease in carbon release to the atmosphere similar in size to current anthropogenic carbon emissions. The primary reason for uncertainty is that the mechanisms of plant respiratory responses to elevated [CO 2 ] have not been resolved (3,(5)(6)(7)(8). This knowledge gap also restricts our understanding at the tissue and whole-plant scales of how elevated [CO 2 ] impacts growth and crop yield. Our research tested the hypothesis that plants respond to the greater carbon supply resulting from long-term growth at elevated [CO 2 ] through acclimation for increased metabolic capacity and greater respiratory flux. Results and DiscussionThe mechanisms by which field-grown plants respond to growth at elevated [CO 2 ] were investigated in this study by combining genomic analysis with biochemical and physiological phenotyping of soybean in a free-air CO 2 enrichment (FACE) experiment. Soybean was grown over its entire lifecycle in 4 plots at ambient [CO 2 ] (Ϸ380 mol⅐mol Ϫ1 ) and 4 plots at elevated [CO 2 ] (Ϸ550 mol⅐mol Ϫ1 ). This model system featured: (i...

It is anticipated that enrichment of the atmosphere with CO 2 will increase photosynthetic carbon assimilation in C3 plants. Analysis

There is growing interest in measuring the antioxidant status of plant tissues. This protocol describes the oxygen radical absorbance capacity (ORAC) assay, which measures antioxidant inhibition of peroxyl radical-induced oxidations and is a measure of total antioxidant capacity. The assay is performed in a microplate and is assessed with a 96-well multi-detection plate reader. Total antioxidant capacity of 64 experimental samples can easily be analyzed in 1 d. This assay is presented along with rapid assays for total phenolic content and total ascorbate content. Overall, these assays provide a general diagnostic tool of the antioxidant capacity in leaf tissue extracts.

Crops losses to tropospheric ozone (O3) in the United