Mass Spectrometry Imaging Analysis of Metabolic Changes in Green and Red Tomato Fruits Exposed to Drought Stress

Plant metabolism is altered in response to various environmental changes. In vegetable crops such as tomato (Solanum lycopersicum), the metabolic composition of fruits varies depending on the variety or cultivar as well as the cultivation method used. Few studies have examined the metabolic fluctuations in fruits under stress conditions, such as drought. We previously examined the metabolomes of mature green tomato fruits, which undergo drastic changes in chemical composition during ripening, and mature red fruits in response to drought stress. We detected or predicted fluctuations in the levels of fatty acids and phospholipid constituents, such as inositol and ethanolamine. In this study, we determined the localizations of these metabolites in fruits using mass spectrometry imaging. The accumulation patterns of stearic acid and palmitic acid were similar, but unlike these fatty acids, oleic acid accumulated to high levels in the placenta. Inositol is involved in various physiological processes; under drought conditions, this metabolite is synthesized by a different pathway compared to under normal conditions. The biosynthesis of pectin, a component of the gel surrounding the seeds, was suppressed under drought stress but increased in seeds. We propose that under drought conditions, a shift to phospholipid biosynthesis occurs that protects seeds from dehydration.