The present study deals with the effects of osmotic stress, $\Psi_s$, temperature (T) and zinc (Zn) concentrations (in the physiological range) on the germination processes of seeds in three plant species of different ecological affiliation, namely: Senna alexandrina, Senna italica (native to hot deserts) and Senna occidentalis (a wild mesophytic plant). Total content, specific and allocation of soluble and potentially free amino acids in the embryonic axis (radicle and hypocotyl) were determined. It was observed that, addition of zinc to the seed incubation medium improved the adjustment of radicles to water deficiency conditions through increasing the allocation of free amino acids into the radicles and hence increasing the osmotic potentials of radicles. Also, zinc induced additional adaptation of the plants to extreme temperatures through increasing total osmotically active amino acids in the radicle. While, glutamic was the dominant amino acid in radicles of S. alexandrina and S. italica (xerophytes), proline was the dominant in S. occidentalis (mesophyte). The statistical analysis indicated that the trifactorial interaction ($\Psi_s \times T \times Zn$) had the major effect on the total free amino acids of the three plants.