Free amino aciel contents of tomato fruit grown under water and salinity stresses

The taste of the tomato fruit is known to depend on the kind and amount of free amino acids present. We investigated the differences in free amino acid contents of tomato fruit grown under water and salinity stresses. Water stress was applied by restricting the irrigation to 25% of control. Salinity stress was applied by irrigating with a solution with an electric conductivity of 4.0 dS m(-1) (cf. Control EC of 1.6 dS m(-1)). Glutamate content on a fresh weight basis was unaffected by water stress, but increased 2-fold under salinity stress. This increase may contribute to an improvement in fruit taste. Under water stress and on a dry weight basis, proline and gamma-aminobutyrate were increased, asparagine, glutamine and arginine were decreased, and other amino acids were unaffected. In contrast, under salinity stress, all amino acids were increased. We conclude that a net accumulation of amino acids occurred in tomato fruit under salinity stress, but not under water stress. Furthermore, the accumulation of proline and gamma-aminobutyrate was a common response in tomato fruit under water and salinity stresses. Therefore, these two amino acids may help to defend against water and salinity stresses in tomato fruit.