13C-nmr Spectroscopy to Monitor Sugars in Pitch of Internodes of a sh2 Corn at Developmental Stages

Sugars move through stalks to be deposited in kernels in sweet corn (Zea mays L.). Concentrations of sugars in stalks change as plants pass through developmental stages. To follow such changes, carbon-13 nuclear magnetic resonance spectroscopy (C-nmr), a technology that can measure concentrations of sugars in tissues, was compared with analysis by high-performance liquid chromatography (HPLC). A shrunken-2 hybrid (cv. Illini Gold), was monitored from mid-whorl to fresh-market maturity (R3). Internodes near the base of the stalk, just below the ear, and between an ear and the tassel were sampled at each developmental stage. Chemical shifts in C-nmr spectra were measured in parts per million hertz (ppm) down-field relative to tetramethyl silane. Through silk emergence (R1) C-nmr spectra were similar regardless of internode, having line positions between 60 and 105 ppm. Unique lines for glucose, fructose, and sucrose were at 96, 98, and 104 ppm, respectively, and mole fractions were similar to those determined by HPLC. The highest concentrations were recorded at R1 for sucrose (26.1 mg·mL-1), from tasseling (VT) through R3 for fructose (avg. 30.4 mg·mL-1), and from VT to R1 for glucose (avg. 32 mg·mL-1). Carbon-13 nuclear magnetic resonance spectroscopy can be used, with minimal sample handling, to monitor sugar concentrations in sweet corn.