Exogenous ALA applied on different plant parts promotes tomato fruit quality and GABA synthesis.

Introduction: Tomato fruit are rich in Methods: To investigate the effects of 5-aminolevulinic acid (ALA) on fruit quality and GABA synthesis in greenhouse tomatoes, the tomato cultivar ( Results and discussion: The results demonstrated that exogenous ALA application to different parts of greenhouse-grown tomato plants substantially increased single-fruit weight by 42.37%-76.24%, soluble sugar content by 78.51%-94.52%, soluble solids by 9.09%-41.71%, soluble protein by 82.71%-241.05%, and ascorbic acid content by 1.31%-5.06% in mature tomatoes. And it reduced the organic acid content of the fruit by 12.81%-33.61%. Moreover, ALA applied at different parts of plants substantially enhanced the free amino acid content by 11.22%-16.50%, among them, umami amino acid content by 7.26%-20.13%. Besides, GABA content in mature tomato fruits was increased by 214.58%-433.32 across the different application parts. Exogenous ALA application at different sites regulates the activity of glutamate acid decarboxylase (GAD) and increases the content of glutamate for GABA synthesis pathway during tomato fruit development, thereby affecting the GABA content. In summary, exogenous ALA applied at different parts of tomato plants regulates the metabolism of amino acids and enhances the biosynthesis of GABA, which promotes the nutrient quality of the fruit.