Baptism of Tomato Seedlings by Osmotic Stress Alters ABA Relations and Improves Tolerance to Salt and Water Stress after Transplant

During germination and early seedling development plants sense and adapt to the growing conditions, which is important for stand establishment and crop yield. ABA biosynthesis and signalling are involved in the control of specific phases of development with a large protective effect against environmental stresses via expression of protective proteins (eg. dehydrins, LEA). It has been hypothesized that, at the early post-germination stage, seedlings monitor the osmotic environment with physiological consequences manifested during the transition to vegetative growth. 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. 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 changes 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.