Growth-promoting bacteria and natural regulators mitigate salt toxicity and improve rapeseed plant performance.

Salinity is a major environmental stress that limits plant production and portraits a critical challenge to food security in the world. In this research, the impacts of plant growth-promoting bacteria (Pseudomonas RS-198 and Azospirillum brasilense RS-SP7) and foliar application of plant hormones (salicylic acid 1 mM and jasmonic acid 0.5 mM) on alleviating the harmful effects of salt stress in rapeseed plants (Brassica napus cv. okapi) were examined under greenhouse condition. Salt stress diminished rapeseed biomass, leaf area, water content, nitrogen, phosphorus, potassium, calcium, magnesium, and chlorophyll content, while it increased sodium content, endogenous salicylic and jasmonic acids, osmolyte production, H2O2 and O2•- generations, TBARS content, and antioxidant enzyme activities. Plant growth, nutrient content, leaf expansion, osmolyte production, and antioxidant enzyme activities were increased, but oxidative and osmotic stress indicators were decreased by bacteria inoculation + salicylic acid under salt stress. Antioxidant enzyme activities were amplified by jasmonic acid treatments under salt stress, although rapeseed growth was not generally affected by jasmonic acid. Bacterial + hormonal treatments were superior to individual treatments in reducing detrimental effects of salt stress. The best treatment in rectifying rapeseed growth under salt stress was combination of Pseudomonas and salicylic acid. This combination attenuated destructive salinity properties and subsequently amended rapeseed growth via enhancing endogenous salicylic acid content and some essential nutrients such as potassium, phosphorus, and magnesium.

Biochar and lignite affect H+-ATPase and H+-PPase activities in root tonoplast and nutrient contents of mung bean under salt stress.

This research was conducted to evaluate effects of biochar (50 and 100 g kg-1 soil) and lignite (50 and 100 g kg-1 soil) treatments on H+-ATPase and H+-PPase activity of root tonoplast, nutrient content, and performance of mung bean under salt stress. High saline conditions increased H+-ATPase and H+-PPase activities in root tonoplast, sodium (Na) content, reactive oxygen species (H2O2 and O2-) generation, relative electrolyte leakage (REL) and 2,2-Diphenyl-1-picrylhydrazyl (DPPH) activity in root and leaf, but decreased relative water content (RWC), chlorophyll content index, leaf area, potassium (K), calcium (Ca), magnesium (Mg), zinc (Zn) and iron (Fe) content of plant tissues, root and shoot dry weight of mung bean. Lignite and biochar treatments decreased the H+-ATPase and H+-PPase activities of root tonoplast under salt stress. Moreover, these treatments increased the cation exchange capacity of soil and nutrient values in plant tissues. Biochar and lignite diminished the generation of reactive oxygen species and DPPH activity in root and leaf cells, and these superior effects improved chlorophyll content index, leaf area and growth of mung bean under both conditions. In general, the results of this study demonstrated that biochar and lignite decreased the entry of Na ion into the cells, enriched plant cells with nutrients, and consequently improved mung bean performance under salt toxicity.

Effect of biochar on growth and ion contents of bean plant under saline condition.

A pot experiment was conducted with three biochar ratios (non-biochar, 5, and 10% total pot mass) and three salinities (control, 6, and 12 dSm-1 sodium chloride) treatments. At the flowering stage, we harvested common bean (Phaseolus vulgaris L. cv. Derakhshan) plants and measured growth characteristics and nutrient contents. As an average, salt stress decreased shoot and root dry weight, leaf area, relative water content, chlorophyll fluorescence (Fv/Fm) and leaf chlorophyll content, however, increased root length, sodium (Na) content of root and shoot, Na uptake, and translocation of bean plants, compared to control. On the other hand, the growth and ion contents of bean were affected positively by use of biochar, but Na translocation was not changed. Addition of biochar improved content of chlorophylls a, b, and total, and potassium (K), calcium (Ca), and magnesium (Mg) contents, while, diminished Na content and uptakes. Moreover, in case of measured parameters, 10% biochar was more effective compared to 5%. Overall, biochar enhanced growth of a bean under saline condition, which may have contributed to the reduction of Na uptake and enhance of K, Ca, and Mg contents.

Nano-silicon alters antioxidant activities of soybean seedlings under salt toxicity.

Materials with a particle size less than 100 nm are classified as nano-materials. The physical and chemical properties of nano-materials can vary considerably from those of bulk materials of the same composition. Silicon (Si) still fails to get recognized as an essential nutrient for plant growth and development, however the beneficial effects in terms of growth, biotic and abiotic stress resistance have been indicated in a variety of plant species for their growth. The aim of this study was to investigate the effects of different nano-silicon rates on the growth and antioxidant activities of soybean (Glycine max L. cv. M7) under salt stress. The results showed that salinity decreased shoot and root dry weight, potassium (K+) concentration in the root and leaf; however, increased sodium (Na+) concentration, catalase, peroxidase, ascorbate peroxidase and superoxide dismutase activities, phenolic components, ascorbic acid and α-tocopherol contents, lipid peroxidation, hydrogen peroxide, and oxygen radical's concentration. Between the treatments, 0.5 and 1 mM of nanosilicon oxide (nano-SiO2) improved shoot and root growth of seedlings. In contrast, a foliar application of SiO2 at 2 mM reduced the soybean growth. Overall, exogenous nano-silicon alleviated the salt stress by increase in K+ concentration, antioxidant activities, non-enzymatic compounds and decreasing of Na+ concentration, lipid peroxidation, and reactive oxygen species production.

Antioxidant enzyme and osmotic adjustment changes in bean seedlings as affected by biochar under salt stress.

Salinity damaged cellular membranes through overproduction of reactive oxygen species (ROS), while osmolytes and antioxidant capacities play a vital role in protecting plants from salinity caused oxidative damages. Biochar also could alleviate the negative impacts of salt stress in crops. The pot experiment was conducted to investigate the effects of biochar on some antioxidant enzyme activities and osmolyte adjustments of common bean (Phaseolus vulgaris L. cv. Derakhshan) under salinity stress. Bean plants were subjected to three salinity levels (non-saline, 6 and 12 dSm-1 of NaCl) and biochar treatments (non-biochar, 10% and 20% total pot mass). Shoot and root dry weights of bean were decreased at two salt stress treatments. Salinity increased the activity of catalase (CAT), ascorbate peroxidase (APX), peroxidase (POD), polyphenol oxidase (PPO) and superoxide dismutase (SOD), and the content of malondialdehyde (MDA), oxygen radicals (O2•-), and hydrogen peroxide (H2O2) in leaf and root compared to control. Additionally, increased magnitudes of proline, glycine betaine, soluble sugar and soluble protein contents were more pronounced under 12 dSm-1 NaCl than those under 6 dSm-1 NaCl. In contrast, biochar applied to soil enhanced the shoot and root dry weight in comparison with the non-biochar treatment. Furthermore, all of the antioxidant activities of seedlings in soil treated with biochar, particularly at 20% biochar, declined. With the addition of biochar, the contents of MDA, O2•- and H2O2 displayed remarkable decrease, and the osmotic substances accumulation in leaves and roots also reduced. The presented results supported the view that biochar can contribute to protect common bean seedlings against NaCl stress by alleviating the oxidative stress.