During germination and early seedling development, plants sense and adapt to their growing conditions, which is important for stand establishment and crop yield. The application of osmotic stress (-0.5 MPa PEG) to young tomato seedlings (termed osmopriming) just after germination by complete immersion for a 5-day period, induced adaptation to both drought and salinity stress, allowing greater vegetative biomass production and maintenance of a better water and photosynthetic status. Although the molecular mechanisms by which this stress memory works are not known, changes in the levels of key signalling molecules or transcription factors, linked to some epigenetic changes, could enable long-term changes in gene expression and allow a quicker/more sensitive response to subsequent stresses. It was hypothesized that ABA biosynthesis and signalling plays an important role in these processes, not only in the control of specific phases of development with a large protective effect against environmental stresses via expression of protective proteins (eg. dehydrins, LEA, HSP), but also in the regulation of stomatal conductance in the adult plants. ABA analysis of the young leaves revealed important differences between control and osmoprimed plants when cultivated under optimal and stress conditions. In the absence of stress, the ABA levels in the adult osmoprimed plants were increased by 7-times when compared to the non-osmoprimed plants, while an additional 4-fold increase was registered under high salinity. The physiological and molecular roles of the ABA relations of osmoprimed plants are under investigation. These phenomena may facilitate plant adaptation to harmful conditions and could result from the retention of a stressful memory.