Title : GABA Shunt Pathway in Germinating Seeds of Wheat (Triticum aestivum L.) and Barely (Hordeum vulgare L.) under Salt Stress
Abstract:
Soil salinity is one of the major abiotic stresses affecting seed germination, crops growth and productivity. In this study three wheat cultivars (Triticum aestiveum L) (Hurani75, Um Qayes and Sham1) seeds and three barley cultivars (Hordeum vulgare L.) (Rum, Acsad175, and Athrouh) seeds were treated with different concentration of slat stress (NaCl) to investigate the effect of such treatments on seed germination stage physiology and metabolism through the characterization of seeds germination pattern, GABA shunt metabolite levels (GABA, Glutamate and Alanine) and glutamate decarboxylase (GAD) expression using RT-PCR. A trend of decreasing germination percentage with increasing NaCl concentrations was observed in all cultivars. At 200 mM NaCl, the germination was highly inhibited. The inhibition in daily recorded pattern was high in wheat when compared to barley in all cultivars under all NaCl treatments. Under all salt stress treatments, our data showed significant (P≤0.01-0.05) increase with positive correlation (r = 0.50-0.99) between level of GABA shunt metabolites (GABA, alanine, and glutamate) and salt concentration in all wheat and barley cultivars daily for 5 days, and after 5 days, separately. Increased GABA levels were associated with a small but significant (P≤0.01-0.05) increase in the content of Ala and Glu daily and after 5 days in all wheat and barley cultivars. In all NaCl treatments, the transcription of GAD in term of RNA level showed significant (P≤0.01-0.05) increase in all cultivars with positive correlation (r = 0.50-0.98). At 200 mM NaCl, the level of GAD RNA transcripts was significantly (P≤0.01-0.05) decreased. There were increased changes in GAD expression with time because of increasing stress levels. Data showed an association between GAD RNA transcription and the response of germinating seeds to salt stress in terms of GABA shunt metabolites accumulation. The elevated expression of the GAD under salinity stress suggests the need for elevated activity of the GAD-mediated conversion of glutamate to GABA during seed germinating, which provides alternative metabolic routes to the respiratory machinery, balancing carbon and nitrogen metabolism and osmolytes synthesis in wheat and barley germinating seeds under environmental stress. Our study determine the effects of NaCl treatments on embryo development and GABA shunt pathway metabolism of germinating seeds in wheat and barley. Also, this study strongly showed the functional role of GABA shunt pathway during seed germination under salt stress treatments in Jordanian cultivated wheat and barley plants.
