Chemical exchange saturation transfer magnetic resonance imaging for metabolic mapping of ripening tomato fruit:...

Chemical Exchange Saturation Transfer Magnetic Resonance Imaging (CEST-MRI) is an established tool in animal or human MRI to indirectly visualize metabolites in vivo. We used CEST-MRI to map the major metabolites in tomato fruit at tissue level throughout ripening. Phantom experiments showed a CEST effect in the 1 and 3 ppm chemical shifts for major soluble sugars and free amino acids, respectively, and a tendency for the CEST signal to decrease from pH 4.7 to 3.7. Fruit images for hydroxyl or amine moieties were well-contrasted for all ripening stages, showing gradients within and between tissues. Mean hydroxyl-CEST signals correlated with the ex vivo concentrations of soluble sugars of dissected tissues, although this was not the case for amino acids. This approach holds much promise for monitoring composition changes in vivo within a plant organ tissue.