Amino acid pools and enzyme activities of NH3-assimilation (glutamine synthetase, glutamate synthase), proline biosynthesis (pyrroline-5-carboxylate reductase), proline catabolism (proline dehydrogenase, proline oxidase), and ornithine transamination (ornithine transaminase) were determined in control and salinized (140 mM NaCl) calli from tomato roots. Three populations were used: the domestic salt-sensitive Lycopersicon esculentum Mill. cv. P-73, the wild salt-tolerant Lycopersicon pennellii (Correll) D'Arcy, accession PE-47, and their F1interspecific cross, for which the relative growth rate on salt media was intermediate to those of the parents. Compared with control conditions, proline levels increased with NaCl treatments by twofold, threefold, and sixfold in the wild species, the F1hybrid, and the domestic species, respectively. This proline accumulation in the F1and the domestic populations was not modulated by changes in the enzyme activities of proline biosynthesis or catabolism. NaCl tolerance, amino acid (proline, alanine, arginine, asparagine) content, and velocity of enzymes responsible for proline biosynthesis and catabolism are dependent on explant sources (cotyledon, root) from which the F1calli were derived. The comparison of proline (PRO) responses in the different calli and populations indicated (i) various changes in anabolic or catabolic rates of PRO metabolism for a given range of PRO accumulation and (ii) the presence in the F1of both wild and sensitive parent characters in growth and PRO responses. Key words: callus culture, Lycopersicon esculentum, Lycopersicon pennellii, F1tomato, proline synthesis, proline catabolism, salt stress.