Glutamate Receptor Homolog3.4 is Involved in Regulation o Seed Germination Under Salt Stress in Arabidopsis

Seed germination is sensitive to salt stress. ABA and Ca2+ are involved in the regulation of seed germination under salt stress. Ca2+ influx mediated by glutamate receptors (GLRs) plays important roles in many physiological processes in plants. Here, we investigated the correlation of GLRs, Ca2+ and ABA during seed germination in response to salt stress by using Arabidopsis thaliana wild-type and T-DNA insertion knockout mutants of glutamate receptor homolog3.4. We demonstrated that atglr3.4-1 and atglr3.4-2 mutants were more sensitive to NaCl during seed germination and post-germination growth than wild-type plants. Treatments of wild-type seedlings with NaCI evoked a marked elevation in cytosolic Ca2+ activity ([Ca2+](cyt)), and the elevation was inhibited by antagonists of GLRs, while the NaCI-induced elevation in ([Ca2+](cyt)) was impaired in atglr3.4-1 and atglr3.4-2 mutants. Moreover, the mutants exhibited a lower expression of 5053, SOS2 and SOS1, and greater accumulation of Na+ than wild-type seeds in the presence of NaCI. Mutation of AtGLR3.4 rendered the mutants more sensitive to ABA, while overexpression of AtGLR3.4 made the transgenic lines more tolerant to ABA in terms of seed germination. However, there was no difference in ABA content between atglr3.4 mutants and wild-type seeds, accompanied by lower expression of AB13 and AB14 in atglr3.4 mutants when challenged with NaCI. These results demonstrate that AtGLR3.4-mediated Ca2+ influx may be involved in the regulation of seed germination under salt stress by modulating Na+ accumulation through the SOS pathway.