Growth, Physiology, and Abiotic Stress Response to Abscisic Acid in Tomato Seedlings

The effect of abscisic acid (ABA) on growth, abiotic stress tolerance, and physiology of tomato seedlings was investigated. To examine the effect of ABA concentration on growth and abiotic stresses, six ABA concentrations (0, 10, 50, 100, 150, or $200mg{\cdot}L^{-1}$) were applied by foliar spraying once a day for 10 days. The effect of ABA application number was also studied by using different timing at one ABA concentration ($100mg{\cdot}L^{-1}$) once a day for 1, 3, 5, 7, and 9 days. The effect of ABA on physiology of tomato seedlings was examined by using two concentrations (50 and $100mg{\cdot}L^{-1}$) as compared to the control (non-ABA). Foliar application of ABA decreased the growth characteristics of tomato seedlings in a concentration-dependent manner; however, no statically significant difference was observed between the 50 and $100mg{\cdot}L^{-1}$ treatments. Furthermore, although growth parameters decreased statistically with increasing number of ABA treatments, there was no difference between the 3 and 5 application treatments. Application of ABA enhanced stress tolerance (cold and drought) of tomato seedlings by delaying the starting time of wilting point in drought conditions and reducing the relative ion leakage and chilling injury index in low temperature in all treatments. The transpiration rate decreased significantly, while stomatal diffusive resistance increased significantly with increasing ABA concentration. The relative water content decreased significantly during the period without irrigation. However, relative water content increased with increasing ABA concentration. The ABA enhanced drought tolerance of tomato seedlings by delaying the start time of wilting point from day 3 in the control to day 5 and 7 in the 50 and $100mg{\cdot}L^{-1}$ treatments, respectively. Integrating this result data, we can determine the ABA's ability to maintain of seedling quality at low temperature and water deficit condition.