Nitrate Promotes Germination Under Inhibition by NaCl or High Concentration of Glucose

Seed germination, one of the most important stages in a plant's life cycle, can be affected by abiotic stresses, such as salinity. The plant hormone abscisic acid (ABA) and high concentrations of glucose are also known to inhibit germination. In contrast, nitrate is known to stimulate germination in many plants. However, this stimulatory effect has not yet been investigated in the presence of inhibitory effects caused by abiotic stresses, ABA, and glucose. In this study, we show that nitrate can alleviate the inhibitory effects of sodium chloride (NaCl) or high concentrations of glucose on seed germination in Arabidopsis, while it was not able to promote germination that was inhibited by exogenous ABA and mannitol (an inducer of osmotic stress). An analysis of the gene expression involved in the regulation of germination showed that GA20ox1, encoding the gibberellin (GA) synthesis enzyme, SPATULA (SPT), encoding a bHLH transcription factor, and CYP707A2, encoding an ABA catabolic enzyme, were significantly upregulated by the addition of KNO₃ in the presence of NaCl or glucose. Our results suggest the possibility that these genes are involved in the nitrate-mediated control of seed germination in the presence of NaCl or glucose.