Location of sugars in barley seeds during germination by NMR microscopy
The distribution and fluctuation of sugars in germinating barley seeds were examined by 13C nuclear magnetic resonance (NMR) spectroscopy, 1H-NMR imaging and 1H-NMR localized spectroscopy in relation to morphology. Maltose, sucrose, fructose and oils were detected in intact imbibed seeds by 13C-NMR spectra. During the first 6 d of germination, the maltose content increased and the oil content gradually decreased, whilst the levels of sucrose and fructose remained constant. Sugars were located by 1H-NMR images and 1H-NMR localized spectra in the vascular bundle of the seeds as well as in the solubilized endosperm. They were also detected in the shoots. The sugars detected in an 80% ethanol shoot extract were sucrose and glucose, which were located in the vascular bundles but not in the mesophyll cells of the coleoptile. They were also located in the basal part of the shoot, but not above 7 mm from the scutellum. The data suggest that the sugars are primarily transported through the vascular bundles and, at the same time, rapidly incorporated into mesophyll cells in the leaves.