Profiling and visualization of organic acids in grape plants by desorption electrospray ionization imaging

Organic acids play a crucial role in determining the quality of grapes and their derived products, such as wine and juice. Despite their critical role in grapevine physiology and fruit quality, limited research has investigated the distribution of these acids within grape plants. This study employed desorption electrospray ionization (DESI) imaging to rapidly profile and image key organic acids across various grape tissues. By analyzing the ratios of tartaric and malic acids in different tissues, we leveraged DESI's semi-quantitative capabilities. The results not only align with previous quantitative findings but also reveal distinct spatial distributions of these acids. Malic acid was predominantly localized in the cortex and epidermis, while tartaric acid was concentrated in the pith region of stems, stem junctions, and near veins in leaf blades. These patterns suggest tissue-specific biosynthetic activities and provide spatial evidence for multiple active pathways in tartaric acid synthesis within grape plants. Overall, this study advances our understanding of organic acid metabolism in grapes and highlights DESI as a powerful and high throughput tool for obtaining semi-quantitative chemical data with high spatial resolution in plant science.