Metabolomic analysis of Brachypodium distachyon in response to abiotic stress and seed priming application

The arable land area dramatically decreased by environmental stress has become a major concern worldwide. Environmental stress factors, especially salinity and drought, significantly reduce crop quality and yield due to the negative impact on the developmental stages of plants. Understanding the responses of plants against stress can gain new key perspectives on the struggle with stress as well as contribute to the significant improvement on the stress tolerance of the plant system. Seed priming, introduced as a new method for coping with stress, accelerates metabolic responses by awakening the plant memory in the pre-germination period with signal imprints. Thus, when a plant encounter with stress, its defense mechanism passes into the alarm phase faster. Brachypodium distachyon is a uniquely suited monocot model system for grass species, potential biofuel plants, and crucial cereals such as wheat, rice, and barley. In this study, B. distachyon seeds (Bd-21 inbred line) were treated with different concentrations of potassium nitrate (2, 5, and 10 percent KNO3) as chemical priming and distilled water as hydropriming. To examine the effect of seed priming on physiological and metabolic changes of the plants under drought and salinity stress with a time-dependent manner (4 days, 8 days and 12 days) at their vegetative phase, plant height, RWC (relative water content), RMP (relative membrane permeability), and metabolite contents (amino acid and polyamine concentrations by High Performance Liquid Chromatography) were evaluated. Valine, phenylalanine, lysine, arginine, alanine, leucine, and glycine concentrations were increased under drought, while under salinity only valine was increased at all time points. In responses to abiotic stress, the most significant changes were observed at the 12th day of stress, in particular at drought. Compared with non-priming, KNO3 primed groups (5% and 10%) exhibited significantly higher RWC and contents of lysine, glutamate, phenylalanine and aspartic acid, and lower RMP and spermine accumulations. Furthermore, distinctly different accumulation patterns were observed in the proline and polyamine pools of the KNO3 groups showing a possible interaction between KNO3 applications and stress signaling/tolerance responses in B. distachyon under stress. This study highlights the effects of seed priming applications on plant stress responses under drought and salinity stress by investigating gradual metabolites changes.