Plant growth promoting bacteria (PGPR) induce antioxidant tolerance against salinity stress through biochemical and physiological mechanisms

Salinity is one of the most severe abiotic stress in the world. Also, the irrigated lands have been treated with second salinity. Canola is one of the most important industrial crops for oil production all over the world which is affected by salinity. Salt stress causes imbalanced ion hemostasis (Na⁺ and K⁺) and interrupted mineral absorption in canola. Also, salinity stress leads to oxidative stress (production and accumulation of reactive oxygen species (ROS). Accumulation of ROS is extremely dangerous and lethal for plants. As a consequence, canola production is reduced under salinity stress. So, a suitable approach should be found to deal with salinity stress and prevent the loss of production oilseed. Plant growth-promoting rhizobacteria (PGPR) can colonize on the plant root surface and alleviate the salt stress effect by providing minerals like nitrogen, phosphate, and potassium. Also, they alleviate salt stress by phytohormones like auxin (IAA), cytokinin (CK), and abscisic acid (ABA). This study focus on physiological parameters like leaf area (LA), root length (RL), shoot length (SL), chlorophyll fluorescence indexes (F_v/F_m and F_v/F₀), relative water content (RWC), electrolyte leakage index (ELI), photosynthesis pigments (chlorophyll a, b, and carotenoids), Na⁺, and K⁺; and biochemical parameters like malondialdehyde (MDA) content, hydrogen peroxide content (H₂O₂), total protein content, proline, antioxidant capacity, and antioxidant enzyme activities in canola through the inoculation with Enterobacter sp. S16-3 and Pseudomonas sp. C16-2O. This study showed that LA, RL, SL, chlorophyll fluorescence indexes, RWC were significantly increased and ELI was significantly decreased in bacteria inoculated treatments. Also, MDA, H₂O₂ were decreased, and antioxidant capacity, proline, and antioxidant enzymes were increased due to inoculation with these bacteria. Besides, the amount of K⁺ as an index of salinity tolerance significantly increased, and leaf Na⁺ content was significantly decreased.

Seed osmopriming with Ca2+ and K+ improves salt tolerance in quinoa seeds and seedlings by amplifying antioxidant defense and ameliorating the osmotic adjustment process

Salinity restricts seed germination and seedling growth through induction of osmotic and oxidative stresses. Therefore, this study aimed to enhance salinity tolerance in quinoa seed by pre-optimized osmo-priming treatments of CaCl₂ (10 mM, 10 °C, 10 h) and KNO₃ (150 mM, 5 °C, 24 h). The results showed that these treatments developed the cellular defense mechanisms in seeds as 'priming memory' that could improve the physiological and biochemical responses to salinity in post-priming stages. The germination capacity and seedling growth decreased with increasing salinity that was accompanied with a higher content of MDA and H₂O₂. However, the improvement of primed seed vigor against high salinity was explained by increasing the biological defense mechanisms including antioxidant enzymes (CAT, APX, SOD, GPX and PPO) and antioxidant metabolites (DPPH antioxidant activity, phenolics, flavonoids, ascorbic acid), particularly in presence of salt stress. In addition, Ca²⁺ and K⁺ priming acquired salinity tolerance in post-priming stages through a significant increase in the accumulation of proline, glycine-betaine, soluble carbohydrate. Improvement in homeostasis of K⁺/Na⁺ ratio by promoting K⁺ maintenance and Na⁺ exclusion was also found in post-priming stages. These observations may be utilized as effective methods in improving salinity tolerance of quinoa seed germination in saline agriculture by improving the antioxidant system, osmolyte accumulation and mineral nutrient homeostasis.

Proteomic response of barley leaves to salinity

Drought and salinity stresses are adverse environmental factors that affect crop growth and yield. Proteomic analysis offers a new approach to identify a broad spectrum of genes that are expressed in living system. We applied this technique to investigate protein changes that were induced by salinity in barley genotypes (Hordeum vulgare L.), Afzal, as a salt-tolerant genotype and L-527, as a salt-sensitive genotype. The seeds of two genotypes were sown in pot under controlled condition of greenhouse, using a factorial experiment based on a randomized complete block design with three replications. Salt stress was imposed at seedling stage and leaves were collected from control and salt-stressed plant. The Na(+) and K(+) concentrations in leaves changed significantly in response to short-term stress. About 850 spots were reproducibly detected and analyzed on 2-DE gels. Of these, 117 proteins showed significant change under salinity condition in at least one of the genotypes. Mass spectrometry analysis using MALDI-TOF/TOF led to the identification some proteins involved in several salt responsive mechanisms which may increase plant adaptation to salt stress including higher constitutive expression level and upregulation of antioxidant, upregulation of protein involved in signal transduction, protein biosynthesis, ATP generation and photosynthesis. These findings may enhance our understanding of plant molecular response to salinity.