Effects of Plant-Growth-Promoting Rhizobacteria (PGPR) and Cyanobacteria on Botanical Characteristics of Tomato (Solanum lycopersicon L.) Plants.

Tomatoes are an important agricultural product because they contain high concentrations of bioactive substances, such as folate, ascorbate, polyphenols, and carotenoids, as well as many other essential elements. As a result, tomatoes are thought to be extremely beneficial to human health. Chemical fertilizers and insecticides are routinely utilized to maximize tomato production. In this context, microbial inoculations, particularly those containing PGPR, may be utilized in place of chemical fertilizers and pesticides. In this study, we investigated the effects of PGPR (Bacillus subtilis, and Bacillus amyloliquefaciens) and cyanobacteria when utilized alone, and in conjunction with each other, on the growth, quality, and yield of fresh fruits of tomato plants. The results showed that the inoculation significantly increased all measured parameters of tomato plants compared with the control. Combined use of B. subtilis and B. amyloliquefaciens had a positive impact on tomato yield, increasing fruit yield. Moreover, leaflet anatomical characteristics were altered, with increased thickness of the upper epidermis, lower epidermis, palisade tissue, spongy tissue, and vascular bundles. Tomato fruit quality was improved, as measured by an increased number of fruit per plant (76% increase), fruit weight (g; 33% increase), fruit height (cm; 50% increase), fruit diameter (cm; 50%), total soluble solids (TSS; 26% increase), and ascorbic acid (mg/100 g F.W.; 75% increase), relative to the control, in the first season. In addition, fruit chemical contents (N, P, and K) were increased with inoculation. The results suggest that inoculation with B. subtilis and B. amyloliquefaciens could be successfully used to enhance tomato plant growth and yield.

Improving the Tolerance to Salinity Stress in Lettuce Plants (Lactuca sativa L.) Using Exogenous Application of Salicylic Acid, Yeast, and Zeolite.

Salinity is among the most limiting factors of crop production worldwide. This study aims to investigate the influence of the exogenous application of zeolite, yeast, and salicylic acid in alleviating the negative effect of salt stress under field conditions. Lettuce plants (Lactuca sativa L. cv. Batavia) were tested in a split-plot arrangement replicated three times. The salt stress was applied as a whole-plot factor in the concentrations (0 mM, 50 mM, 100 mM, and 150 mM NaCl). After 28 days of sowing, the plants were sprayed twice during the foliage growth with (control, salicylic acid 0.02%, yeast extract 3%, and zeolite 0.5%) as a split-plot factor. The length of roots and shoots, the number and area of leaves, and the biomass accumulation (dry and fresh weights) were measured 50 days after sowing. The concentrations of total soluble sugars, proline, Chlorophylls a and b in leaves have also been quantified. Salt stress significantly reduced the growth and the total chlorophyll of the lettuce plants (p < 0.05) and increased their proline and sugar contents'. Zeolite application improved the growth of lettuce at 0 and 50 mM NaCl, but at the highest salinity level only the number of leaves was improved by 15%. At a mild salinity stress, the application of salicylic acid has significantly (p < 0.05) increased the root length, height of plant, chlorophyll, and proline contents. Regarding the high stress levels (100 and 150 mM NaCl), yeast application showed the best tolerance to salinity stress by improving significantly most of the growth parameters (p < 0.05) but with lower proline, sugar, and chlorophyll contents. In general, foliar spray of yeast extract may offer a good alternative source of nutrients through leaves, leading to a better tolerance of the high salt stress exerted on roots.

Unraveling the roles of brassinosteroids in alleviating drought stress in young Eucalyptus urophylla plants: Implications on redox homeostasis and photosynthetic apparatus.

Water deficit is the most limiting abiotic stress to plants because it affects several physiological and biochemical processes. Brassinosteroids, including 24-epibrassinolide (EBR), are steroids that regulate growth and positively act on gas exchange. This research aims to determine whether EBR can attenuate the negative effects of water deficit, revealing possible contributions of this steroid on photosynthetic machinery of young Eucalyptus urophylla plants under water deficit. The experiment had a completely randomized factorial design with two water conditions (control and water deficit) and three levels of EBR (0, 50, and 100 nM EBR). Water deficit caused a decrease in the levels of total chlorophyll and carotenoids, but these photosynthetic pigments increased by 135 and 226%, respectively, in plants sprayed with EBR when compared to the water deficit + 0 nM EBR treatment. Regarding the antioxidant system, 100 nM EBR induced significant increments in superoxide dismutase (42%), catalase (52%), ascorbate peroxidase (147%), and peroxidase (204%). Steroid application in E. urophylla plants exposed to water deficit increased the effective quantum yield of the photosystem II (PSII) photochemistry and electron transport rate. However, interestingly, it decreased the nonphotochemical quenching and relative energy excess at the PSII level, indicating improvements related to PSII efficiency. This research revealed that application of 100 nM EBR attenuated the negative effects caused by water deficit, being explained by the positive repercussions on antioxidant enzyme activities, chloroplastic pigments, PSII efficiency, electron flux, and net photosynthetic rate.

Parthenium hysterophorus steps up Ca-regulatory pathway in defence against highlight intensities.

Parthenium hysterophorus exhibits tolerance to a great extent against abiotic stresses including high light intensities. In this study, P. hysterophorus was subjected to three different light intensities viz. control (CL, 250 µmol photons m-2 s-1), moderately high (ML, 500 µmol photons m-2 s-1) and high (HL, 1000 µmol photons m-2 s-1) for assessment of biochemical and physiological responses at 3 and 5 days after treatment (DAT). Proteomic responses were also observed at 5 DAT. Level of oxidative stress marker, abundance of H2O2 and O2- was highest in leaves exposed to HL followed by ML treatment. Biomass accumulation, photosynthetic parameters, chloroplast and mitochondrial integrity were also affected by both ML and HL treatments. Differential protein expression data showed modulation of thirty-eight proteins in ML and HL intensities. P. hysterophorus exhibited good ability to survive in ML then HL treatment as demonstrated by enhancement of the antioxidant system and photosynthesis. Furthermore, P. hysterophorus mobilized some key proteins related to calcium signaling, which in turn coordinate physiological homeostasis under stress. Proline and total soluble sugar content were high under stress; however, results of simulated experiment of our study indicate such accumulation of osmolytes may inhibit photon-availability to chloroplast. These results clarify our understanding of the mechanisms underlying the light stress tolerance of P. hysterophorus.

Exogenous Melatonin Counteracts NaCl-Induced Damage by Regulating the Antioxidant System, Proline and Carbohydrates Metabolism in Tomato Seedlings.

Melatonin, a natural agent, has multiple functions in animals as well as in plants. However, its possible roles in plants under abiotic stress are not clear. Nowadays, soil salinity is a major threat to global agriculture because a high soil salt content causes multiple stresses (hyperosmotic, ionic, and oxidative). Therefore, the aim of the present study was to explore: (1) the involvement of melatonin in biosynthesis of photosynthetic pigments and in regulation of photosynthetic enzymes, such as carbonic anhydrase (CA) and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco); (2) the role of melatonin in osmoregulation by proline and carbohydrate metabolism; and (3) the function of melatonin in the antioxidant defense system under salinity. Outcomes of the study reveal that under non-saline conditions, application of melatonin (20 and 50 µM) improved plant growth, viz. shoot length, root length, shoot fresh weight (FW), root FW, shoot dry weight (DW), root DW and leaf area and physio-biochemical parameters [chlorophyll (Chl) a and b, proline (Pro) and total soluble carbohydrates (TSC) content, and increased the activity of CA and Rubisco]. However, tomato seedlings treated with NaCl exhibited enhanced Chl degradation, electrolyte leakage (EL), malondialdehyde (MDA) and reactive oxygen species (ROS; superoxide and hydrogen peroxide). ROS were detected in leaf and root. Interestingly, application of melatonin improved plant growth and reduced EL, MDA and ROS levels through upregulation of photosynthesis enzymes (CA, Rubisco), antioxidant enzymes (superoxide dismutase, catalase, glutathione reductase and ascorbate reductase) and levels of non-enzymatic antioxidants [ascorbate (ASC) and reduced glutathione (GSH)], as well as by affecting the ASC-GSH cycle. Additionally, exogenous melatonin also improved osmoregulation by increasing the content of TSC, Pro and Δ¹-pyrroline-5-carboxylate synthetase activity. These results suggest that melatonin has beneficial effects on tomato seedlings growth under both stress and non-stress conditions. Melatonin's role in tolerance to salt stress may be associated with the regulation of enzymes involved in photosynthesis, the antioxidant system, metabolism of proline and carbohydrate, and the ASC-GSH cycle. Also, melatonin could be responsible for maintaining the high ratios of GSH/GSSG and ASC/DHA.

Serratia liquefaciens KM4 Improves Salt Stress Tolerance in Maize by Regulating Redox Potential, Ion Homeostasis, Leaf Gas Exchange and Stress-Related Gene Expression.

High salinity mitigates crop productivity and quality. Plant growth-promoting soil rhizobacteria (PGPR) improve plant growth and abiotic stress tolerance via mediating various physiological and molecular mechanisms. This study investigated the effects of the PGPR strain Serratia liquefaciens KM4 on the growth and physiological and molecular responsiveness of maize (Zea mays L.) plants under salinity stress (0, 80, and 160 mM NaCl). High salinity significantly reduced plant growth and biomass production, nutrient uptake, leaf relative water content, pigment content, leaf gas exchange attributes, and total flavonoid and phenolic contents in maize. However, osmolyte content (e.g., soluble proteins, proline, and free amino acids), oxidative stress markers, and enzymatic and non-enzymatic antioxidants levels were increased in maize under high salinity. On the other hand, Serratia liquefaciens KM4 inoculation significantly reduced oxidative stress markers, but increased the maize growth and biomass production along with better leaf gas exchange, osmoregulation, antioxidant defense systems, and nutrient uptake under salt stress. Moreover, it was found that all these improvements were accompanied with the upregulation of stress-related genes (APX, CAT, SOD, RBCS, RBCL, H⁺-PPase, HKT1, and NHX1), and downregulation of the key gene in ABA biosynthesis (NCED). Taken together, the results demonstrate the beneficial role of Serratia liquefaciens KM4 in improving plant growth and salt stress tolerance in maize by regulating ion homeostasis, redox potential, leaf gas exchange, and stress-related genes expression.

Genetic Variation and Alleviation of Salinity Stress in Barley (Hordeum vulgare L.).

Barley (Hordeum vulgare L.) represents one of the most important cereals cultivated worldwide. Investigating genetic variability and structure of barley is important for enhancing the crop productivity. This study aimed to investigate the diversity and structure of 40 barley genotypes originated from three European countries (France, the Netherlands, Poland) using amplified fragment length polymorphisms (AFLPs). It also aimed to study 5-aminolevulinic acid (ALA) effect on salinity tolerance of six barley genotypes. The expected heterozygosity (He) diverged from 0.126 to 0.501, with a mean of 0.348. Polymorphic information content (PIC) diverged from 0.103 to 0.482 across barley genotypes, with a mean of 0.316, indicating that barley genotypes are rich in a considerable level of genetic diversity. The 40 barley genotypes were further studied based on their geographical origin (Western Europe and Eastern Europe). The Eastern European region (Poland) has a higher barley variability than the Western European region (France and the Netherlands). Nei's distance-based cluster tree divided the 40 barley accessions into two major clusters; one cluster comprised all the varieties originated from the Eastern European region, while the other major cluster included all accessions originated from the Western European region. Structure analysis results were in a complete concordance with our cluster analysis results. Slaski 2, Damseaux and Urbanowicki genotypes have the highest diversity level, whereas Carmen, Bigo and Cambrinus genotypes have the lowest level. The response of these six varieties to NaCl stress was also investigated. Salt stress (100 mM NaCl) slightly decreased levels of chlorophyll, carotenoid and osmolytes (proteins, soluble sugars, phenolics and flavonoids) in the leaves of Slaski 2, Damseaux and Urbanowicki genotypes at non-significant level, as compared to control samples. However, pigment contents and osmolytes in leaves of Carmen, Bigo and Cambrinus genotypes were significantly decreased by salt stress. Antioxidant enzyme activities were significantly increased in Slaski 2 genotype, but non-significantly increased in Carmen by salt stress. Priming Slaski 2 and Carmen cultivars with ALA under salt stress significantly induced pigment contents, antioxidants enzymes activity and stress-responsive genes expression, relative to NaCl-stressed plants. In conclusion, this study suggested a correlation between variability percentage and degree of salinity resistance. ALA improved salt tolerance in barley.

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 ß-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.