We have used a frequency-selective rotational-echo double-resonance (REDOR) solid-state NMR experiment to measure the concentrations of glycine glycine pairs in proteins (and protein precursors) of intact leaves of plants exposed to both high- and low-CO2 atomospheres. The results are interpreted in terms of differences in cell-wall biosynthesis between plant species. We illustrate this variability by comparing the assimilation of label in cheatgrass and soybean leaves labeled using N-15-fertilizer and (CO2)-C-13 atmospheres. Cheatgrass and soybean are both C-3 plants but differ in their response to a high-CO2 environment. Based on REDOR results, we determined that cheatgrass (a plant that seems likely to flourish in future low-water, high-CO2 environments) routes 2% of the assimilated carbon label that remains in the leaf after 1 h in a 600-ppm (CO2)-C-13 atmosphere to glycine-rich protein (or its precursors), a structural component of cell walls cross-linked to lignins. In contrast, soybean under the same conditions routes none of its assimilated carbon to glycine-rich protein.