The role of exogenous glutamine on germination, plant development and transcriptional expression of some stress-related genes in onion under salt stress

The purpose of this research was to explore the role of glutamine (Gln) on plant germination and growth under salinity [0, 50, 100, 150, 200 mM sodium chloride (NaCl)], and on the activation of some stress-related genes [CuZn-Superoxide Dismutase (SOD), Mn-SOD, L-ascorbate oxidase (AO), DNA Polymerase Delta 1 (POLD)-1, Chaperon (CHAPE) and Heat Shock Protein (HSP)-21], genetic template stability and photosynthetic pigment activation. Under salt stress, 2 mM Gln application reduced the mean germination time (MGT) (4.51 days), increased the coefficient of velocity of germination (CVG) (75.85), germination index (GI) (1.46) and germination percentage (GP) (82%), indicating that it was the best application for germination under stress. Gln promoted the development of aboveground plant organs. 3 mM Gln increased the number of leaves from 5.3 to 13.7 and 4.3 to 6.6 under unstress and stress conditions, respectively. Under salt stress, Gln increased photosynthetic pigments and genomic template stability (GTS) (80%). At 2 mM Gln, total chlorophyll and carotenoid content increased from 1.59 mg · g^-1 TA to 2.23 mg · g^-1 TA and from 0.28 mg · g^-1 TA to 0.37 mg · g^-1 TA, respectively. The effect on gene expression levels varied with the concentration. The application of 2 mM Gln, which enhanced germination and vegetative parameters under stress, caused a raise in CuZn-SOD gene expression and a 43% decrease in the transcriptional expression of the HSP-21 gene as an indicator of the functionality of the repair mechanism. The improved growth of Gln-treated plants under stress suggests that Gln is involved in bridging the energy deficit of the plant by acting as an alternative fuel for metabolic activities under stress.