Visualizing the spatial distribution of metabolites in tomato fruit at different maturity stages by matrix-assisted laser desorption/ionization mass spectrometry imaging

Tomato is one of the highest-value fruit and vegetable crop worldwide, serving as an important source of micronutrients in the human diet. Understanding the spatial distribution changes of critical metabolites during fruit maturation is essential for investigating the physiological roles, nutritional value, and potential functional values of phytochemicals in tomato fruit. However, information on their spatial distribution remains limited. This study aimed to visualize the distribution differences of endogenous metabolites in tomatoes across four maturity stages (from green to red) using matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI). Relative quantification results showed that as the fruit ripened, levels of soluble sugars, amino acids and volatile organic compounds (VOCs) increased significantly at the red ripening stage, while L-hydroxysuccinic acid exhibited an opposite trend, and citric acid initially decreased, then increased. Mass spectrometry imaging revealed that soluble sugars, organic acids, and amino acids were evenly distributed throughout the fruit across all maturity stages. During maturation, nine VOCs transitioned from a widespread distribution in the flesh tissue to concentrating near the peel, suggesting that aromatic compounds predominantly localize in the fruit's outer regions at full maturity. Additionally, a colocalization phylogenetic tree was constructed based on the spatial distribution imaging of each metabolite. These findings provide a deeper understanding of the changes and distribution of phytochemicals during tomato fruit development, offering a scientific basis for breeding, utilization, and production strategies.