Bacillus firmus (SW5) augments salt tolerance in soybean (Glycine max L.) by modulating root system architecture, antioxidant defense systems and stress-responsive genes expression.

Soil salinity is an adverse abiotic factor which reduces plant growth, yield and quality. Plant growth-promoting rhizobacteria (PGPR) have a great potential to enhance growth and alleviate saline stress effects without harming the environment via regulating physiological and molecular processes in plants. This study aimed at investigating Bacillus firmus SW5 effects on the performance of soybean (Glycine max L.) subjected to salt stress (0, 40 and 80 mM NaCl). Salinity stress mitigated the growth and biomass yield, root architecture traits, nutrient acquisition, chlorophyll level, transpiration rate (E), photosynthesis rate (Pn), stomatal conductance (gs), soluble proteins content, soluble sugars content and total phenolics and flavonoid contents of soybean plants. High salinity augmented the levels of osmolytes (glycine betaine and proline), hydrogen peroxide (H2O2), malondialdehyde (MDA) and the activities of antioxidant enzymes (APX, CAT, SOD and POD) in soybean plants. High salinity also induced the expression of antioxidant enzyme-encoding genes (APX, CAT, POD, Fe-SOD) and genes conferring tolerance to salinity (GmVSP, GmPHD2, GmbZIP62, GmWRKY54, GmOLPb, CHS) in soybean plants. On the other hand, inoculation of NaCl-stressed soybean plants with Bacillus firmus SW5 promoted the growth and biomass yield, chlorophyll synthesis, nutrient uptake, gas exchange parameters, osmolytes levels, total phenolic and flavonoid contents, and antioxidant enzymes activities, in comparison with the plants treated with NaCl alone. Bacillus firmus SW5 inoculation also significantly reduced the IC50 values for both DPPH and β-carotene-linoleic acid assays and indicated higher antioxidant activities in salt-stressed plants. Furthermore, contents of H2O2 and MDA were alleviated in salinity-stressed soybean plants inoculated with Bacillus firmus SW5, in comparison with those in plants exposed to NaCl alone. The antioxidant enzyme-encoding genes and stress-related genes exhibited the highest expression levels in soybean plants inoculated with Bacillus firmus SW5 and treated with 80 mM NaCl. Taken together, our results demonstrate the crucial role of Bacillus firmus SW5 in ameliorating the adverse effects of high salinity on soybean growth and performance via altering the root system architecture and inducing the antioxidant defense systems and stress-responsive genes expression.

El-Esawi MA ，Alaraidh IA ，Alsahli AA ，Alamri SA ，Ali HM ，Alayafi AA ... -  《-》

Halotolerant Rhizobacterial Strains Mitigate the Adverse Effects of NaCl Stress in Soybean Seedlings.

Salinity is one of the major abiotic constraints that hinder health and quality of crops. Conversely, halotolerant plant growth-promoting rhizospheric (PGPR) bacteria are considered biologically safe for alleviating salinity stress. We isolated halotolerant PGPR strains from the rhizospheric soil of Artemisia princeps, Chenopodium ficifolium, Echinochloa crus-galli, and Oenothera biennis plants; overall, 126 strains were isolated. The plant growth-promoting traits of these isolates were studied by inoculating them with the soil used to grow soybean plants under normal and salt stress (NaCl; 200 mM) conditions. The isolates identified as positive for growth-promoting activities were subjected to molecular identification. Out of 126 isolates, five strains-Arthrobacter woluwensis (AK1), Microbacterium oxydans (AK2), Arthrobacter aurescens (AK3), Bacillus megaterium (AK4), and Bacillus aryabhattai (AK5)-were identified to be highly tolerant to salt stress and demonstrated several plant growth-promoting traits like increased production of indole-3-acetic acid (IAA), gibberellin (GA), and siderophores and increased phosphate solubilization. These strains were inoculated in the soil of soybean plants grown under salt stress (NaCl; 200 mM) and various physiological and morphological parameters of plants were studied. The results showed that the microbial inoculation elevated the antioxidant (SOD and GSH) level and K+ uptake and reduced the Na+ ion concentration. Moreover, inoculation of these microbes significantly lowered the ABA level and increased plant growth attributes and chlorophyll content in soybean plants under 200 mM NaCl stress. The salt-tolerant gene GmST1 was highly expressed with the highest expression of 42.85% in AK1-treated plants, whereas the lowest expression observed was 13.46% in AK5-treated plants. Similarly, expression of the IAA regulating gene GmLAX3 was highly depleted in salt-stressed plants by 38.92%, which was upregulated from 11.26% to 43.13% upon inoculation with the microorganism. Our results showed that the salt stress-resistant microorganism used in these experiments could be a potential biofertilizer to mitigate the detrimental effects of salt stress in plants via regulation of phytohormones and gene expression.

Khan MA ，Asaf S ，Khan AL ，Adhikari A ，Jan R ，Ali S ，Imran M ，Kim KM ，Lee IJ ... -  《-》

Seed priming and foliar application with jasmonic acid enhance salinity stress tolerance of soybean (Glycine max L.) seedlings.

Jasmonic acid (JA) is an important molecule that has a regulatory effect on many physiological processes in plant growth and development under abiotic stress. This study investigated the effect of 60 μmol L-1 of JA in seed priming (P) at 15 °C in darkness for 24 h, foliar application (F), and/or their combination effect (P + F) on two soybean cultivars - 'Nannong 99-6' (salt tolerant) and 'Lee 68' (salt sensitive) - under salinity stress (100 mmol L-1 sodium chloride (NaCl)). Salinity stress reduced seedling growth and biomass compared with that in the control condition. Priming and foliar application with JA and/or their combination significantly improved water potential, osmotic potential, water use efficiency, and relative water content of both cultivars under salinity stress. Similarly, seed priming with JA, foliar application of JA, and/or their combination significantly improved the following properties under salinity stress compared with the untreated seedlings: net photosynthetic rate by 68.03%, 59.85%, and 76.67% respectively; transpiration rate by 74.85%, 55.10%, and 80.26% respectively; stomatal conductance by 69.88%, 78.25%, and 26.24% respectively; intercellular carbon dioxide concentration by 61.64%, 40.06%, and 65.79% respectively; and total chlorophyll content by 47.41%, 41.02%, and 55.73% respectively. Soybean plants primed, sprayed with JA, or treated with their combination enhanced the chlorophyll fluorescence, which was damaged by salinity stress. JA treatments improved abscisic acid, gibberellic acid, and JA levels by 60.57%, 62.50% and 52.25% respectively under salt stress compared with those in the control condition. The transcriptional levels of the FeSOD, POD, CAT, and APX genes increased significantly in the NaCl-stressed seedlings irrespective of JA treatments. Moreover, JA treatment resulted in a reduction of sodium ion concentration and an increase of potassium ion concentrations in the leaf and root of both cultivars regardless of salinity stress. Monodehydroascorbate reductase, dehydroascorbate reductase, and proline contents decreased in the seedlings treated with JA under salinity stress, whereas the ascorbate content increased with JA treatment combined with NaCl stress. The application of 60 μmol L-1 JA improved plant growth by regulating the interaction between plant hormones and hydrogen peroxide, which may be involved in auxin signaling and stomatal closure under salt stress. These methods could efficiently protect early seedlings and alleviate salt stress damage and provide possibilities for use in improving soybean growth and inducing tolerance against excessive soil salinity. © 2020 Society of Chemical Industry.

Sheteiwy MS ，Shao H ，Qi W ，Daly P ，Sharma A ，Shaghaleh H ，Hamoud YA ，El-Esawi MA ，Pan R ，Wan Q ，Lu H ... -  《-》

Chitosan Modified Biochar Increases Soybean (Glycine max L.) Resistance to Salt-Stress by Augmenting Root Morphology, Antioxidant Defense Mechanisms and the Expression of Stress-Responsive Genes.

Mehmood S ，Ahmed W ，Ikram M ，Imtiaz M ，Mahmood S ，Tu S ，Chen D ... -  《Plants-Basel》

Halotolerant plant-growth promoting rhizobacteria modulate gene expression and osmolyte production to improve salinity tolerance and growth in Capsicum annum L.

Yasin NA ，Akram W ，Khan WU ，Ahmad SR ，Ahmad A ，Ali A ... -  《-》