QUANTITATIVE-EVALUATION OF NMR AND MRI METHODS TO MEASURE SUCROSE CONCENTRATIONS IN PLANTS

Developing pea (Pisum sativum L.) seeds were chosen to evaluate the pe rformance of various nuclear magnetic resonance (NMR) and magnetic res onance imaging (MRI) methods of detecting sucrose in plants. The metho ds included chemical shift selective imaging (CHESS), heteronuclear co rrelation via C-13-H-1 coupling (HMQC), and homonuclear correlation vi a H-1-H-1 coupling (DQF). The same experiments were also performed on sucrose phantom samples to evaluate the methods in the absence of the line broadening observed in plant systems. Using the spin echo techniq ue for multi-slice imaging, we could discern the detailed internal str ucture of the intact seed with a resolution of tens of microns. The pr oton spin-lattice relaxation time and linewidth as a function of the a ge of the seed were measured to optimize the efficiency of the NMR and MR experiments. The age-dependent changes in these NMR parameters are consistent with the accumulation of insoluble starch as age increases . Both the NMR and MRI results are in accord with the results of chemi cal analysis, which reveal that the sucrose concentration is higher in the embryo than in the seed coat, and glucose is at low concentration throughout the seed. Of the three methods for proton observation, the enhanced version of the CHESS approach (CD-CHESS) provides the best c ombination of sucrose detection and water suppression. Direct observat ion of C-13 is preferable to indirect detection using HMQC because of water signal bleed-through in samples with large (>200 Hz) linewidths.