Fig. 2.

Effect of [CO₂] on the D6^S/D6^R isotopomer ratio of photosynthetically generated glucose moieties in sunflower (H. annuus). (A) Deuterium NMR spectrum of a glucose derivative displaying one signal for each of the seven isotopomers of glucose. The signals’ integrals are proportional to the isotopomer abundances. (B) Excerpts of deuterium NMR spectra of glucose prepared from sunflower leaf starch, showing signals arising from the D6^S and D6^R isotopomers of the C6H₂ group of glucose. The solid and dashed spectra were acquired from glucose formed at 280 ppm and 1,500 ppm CO₂, respectively. The dashed spectrum has been shifted sideways to ease comparison. (C) Dependence of the D6^S/D6^R ratio of glucose from sunflower leaf starch on 1/[CO₂] (in units of 10⁻³ ppm⁻¹) during growth [r² = 0.88, slope 0.057 ±0.006 (SEM), P < 10⁻⁷, n = 17, individual plants except for 180 and 280 ppm, where material from two to four plants had to be pooled for each sample].