Soil salinity is one of the most significant abiotic stresses limiting plant growth. The ability of plant cells to adapt and survive under salt stress conditions involves triggering a network of signaling events including hormones such as abscisic acid (ABA) known to regulate many important aspects of growth and development. ABA is also known to play a critical role in stress responses such as the regulation of seed germination under salt and osmotic stress. Components of the gibberellic acid (GA) signaling pathway have also been shown to regulate germination; however, the involvement of GA signaling in salt and osmotic stress is largely unexamined. Here, we examined the responses of mutants in the GA signaling pathway (rgl2 and spy) and in the ABA signaling pathway (abi3 and abi5) to salt (NaCl) and osmotic (mannitol) stress during seed germination and early seedling development. Several mutants show resistance to increased levels of both salt and osmotic stress at germination and later stages of seedling development suggesting a role for ABA and GA signaling in these processes. qRT-PCR was employed to determine the effect of salt stress on seed germination via transcriptional control of the components in GA or ABA signaling pathways. We found that RGL2, ABI3, and ABI5 transcripts are greatly induced by NaCl in wildtype plants, but show little if any induction by NaCl in mutant backgrounds suggesting that this regulation of induction during salt stress may occur through ABA–GA crosstalk. Overall, our results indicate that each of the ABA and GA signaling pathways is individually involved in regulation of various seedling developmental stages under stress conditions. In addition, these two hormone pathways appear to be interacting in the regulation of germination and early seedling growth under salt and osmotic stress conditions.
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