NMR study of low subcellular pH during the development of cherry tomato fruit

Abstract

Changes in metabolites (organic acids, sugars and amino acids) and subcellular pH were studied during fruit development of cherry tomato (Lycopersicon esculentum Mill. var. cerasiformae). Fructose and glucose were the major sugars, whereas citrate and malate the two major organic acids. At different stages of fruit development, vacuolar and cytoplasmic pH changes were followed by in vivo ¹³C and ³¹P NMR spectroscopy. Fruit compartments had a cytoplasmic pH around 7.1 as early as the cell-divi-sion and -expansion stages. The vacuolar pH measured by in vivo ¹³C NMR spectroscopy decreased from 4.5 to 3.6. Concomitantly, strong accumulation of γ-aminobutyric acid (GABA) was observed during the first 15 days after anthesis and glutamate decarboxylase (GAD) activity increased 10-fold during the first 8 days of development. The relationships between organic acid biosynthesis and storage, GABA produc-tion, and subcellular pH changes during development of cherry tomato fruit are discussed.