Roots Of Salt-stressed Plants Research Articles

Physiological and biochemical responses of soybean seedlings (Glycine max L.) to α-tocopherol treatment under salt stress

Background. Salinity is one of the most important factors affecting the growth and productivity of plants. It creates stressful conditions for legumes at the initial phases of ontogenesis. The prospects of exogenous α-tocopherol usage to increase the salt resistance of Glycine max L. were studied. The aim of the work was to study the influence of salt stress and α-tocopherol on the growth of soybean and indicators characteri­zing the antioxidant system functioning. Materials and methods. Soybean seedlings of the Oksana variety were the objects of our study. Seeds of the control group were soaked in distilled water, seeds of the experimental groups – in α-Toc acetic solutions in concentrations (0.01; 0.1; 0.5; 1.0 g/L). A 100 mM sodium chloride solution was used to create salinity. The samples of cotyledons, hypocotyls and primary roots of 10-day-old soybean were used for determination of biochemical parameters. Germination of seeds, raw weight, length of soybean hypocotyls and roots, content of TBA-reactive substances, carbonyl groups of oxidatively modified proteins, proline, catalase and ascorbate peroxidase activity were determined. Results. It was established that salinity caused inhibition of soybean seed germination and growth. Pretreatment of soybean seeds with α-Toc (0.1 and 0.5 g/L) effectively increased germination and improved growth indicators of soybean. An increase in TBA-reactive substances and oxidatively modified proteins in hypocotyls and roots of salt-stressed plants was recorded. α-Toc reduced the level of peroxidation and oxidatively modified proteins of soybean seedlings under salinity. Proline synthesis increased during the development of the salt stress reaction, and its accumulation is an adaptive response of soybean plants. The pretreatment of α-Toc caused a significant increase of proline and stimulated catalase and ascorbate peroxidase activity in soybean seedling tissues under salt stress. However, a high concentration of α-Toc (1.0 g/L) slowed down the activity of antioxidant enzymes. Conclusions. Our study suggests the participation of α-Toc in the formation of legumes salt resistance. The α-Toc pretreatment of soybean seeds improved germination and enhanced growth processes, normalized the oxidative state of the salt-stressed soybean seedlings by inhibiting peroxidation and reducing the degree of oxidatively modified proteins, stimulating the activity of antioxidant enzymes, and increasing the content of proline.

Purines enrich root-associated Pseudomonas and improve wild soybean growth under salt stress

The root-associated microbiota plays an important role in the response to environmental stress. However, the underlying mechanisms controlling the interaction between salt-stressed plants and microbiota are poorly understood. Here, by focusing on a salt-tolerant plant wild soybean (Glycine soja), we demonstrate that highly conserved microbes dominated by Pseudomonas are enriched in the root and rhizosphere microbiota of salt-stressed plant. Two corresponding Pseudomonas isolates are confirmed to enhance the salt tolerance of wild soybean. Shotgun metagenomic and metatranscriptomic sequencing reveal that motility-associated genes, mainly chemotaxis and flagellar assembly, are significantly enriched and expressed in salt-treated samples. We further find that roots of salt stressed plants secreted purines, especially xanthine, which induce motility of the Pseudomonas isolates. Moreover, exogenous application for xanthine to non-stressed plants results in Pseudomonas enrichment, reproducing the microbiota shift in salt-stressed root. Finally, Pseudomonas mutant analysis shows that the motility related gene cheW is required for chemotaxis toward xanthine and for enhancing plant salt tolerance. Our study proposes that wild soybean recruits beneficial Pseudomonas species by exudating key metabolites (i.e., purine) against salt stress.

Root Exposure to 5-Aminolevulinic Acid (ALA) Affects Leaf Element Accumulation, Isoprene Emission, Phytohormonal Balance, and Photosynthesis of Salt-Stressed Arundo donax.

Arundo donax has been recognized as a promising crop for biomass production on marginal lands due to its superior productivity and stress tolerance. However, salt stress negatively impacts A. donax growth and photosynthesis. In this study, we tested whether the tolerance of A. donax to salinity stress can be enhanced by the addition of 5-aminolevulinic acid (ALA), a known promoter of plant growth and abiotic stress tolerance. Our results indicated that root exposure to ALA increased the ALA levels in leaves along the A. donax plant profile. ALA enhanced Na+ accumulation in the roots of salt-stressed plants and, at the same time, lowered Na+ concentration in leaves, while a reduced callose amount was found in the root tissue. ALA also improved the photosynthetic performance of salt-stressed apical leaves by stimulating stomatal opening and preventing an increase in the ratio between abscisic acid (ABA) and indol-3-acetic acid (IAA), without affecting leaf methanol emission and plant growth. Supply of ALA to the roots reduced isoprene fluxes from leaves of non-stressed plants, while it sustained isoprene fluxes along the profile of salt-stressed A. donax. Thus, ALA likely interacted with the methylerythritol 4-phosphate (MEP) pathway and modulate the synthesis of either ABA or isoprene under stressful conditions. Overall, our study highlights the effectiveness of ALA supply through soil fertirrigation in preserving the young apical developing leaves from the detrimental effects of salt stress, thus helping of A. donax to cope with salinity and favoring the recovery of the whole plant once the stress is removed.

Growth-Promoting Effect of Rhizobacterium (Bacillus subtilis IB22) in Salt-Stressed Barley Depends on Abscisic Acid Accumulation in the Roots.

An ABA-deficient barley mutant (Az34) and its parental cultivar (Steptoe) were compared. Plants of salt-stressed Az34 (100 mmol m−3 NaCl for 10 days) grown in sand were 40% smaller than those of “Steptoe”, exhibited a lower leaf relative water content and lower ABA concentrations. Rhizosphere inoculation with IB22 increased plant growth of both genotypes. IB22 inoculation raised ABA in roots of salt-stressed plants by supplying ABA exogenously and by up-regulating ABA synthesis gene HvNCED2 and down-regulating ABA catabolic gene HvCYP707A1. Inoculation partially compensated for the inherent ABA deficiency of the mutant. Transcript abundance of HvNCED2 and related HvNCED1 in the absence of inoculation was 10 times higher in roots than in shoots of both mutant and parent, indicating that ABA was mainly synthesized in roots. Under salt stress, accumulation of ABA in the roots of bacteria-treated plants was accompanied by a decline in shoot ABA suggesting bacterial inhibition of ABA transport from roots to shoots. ABA accumulation in the roots of bacteria-treated Az34 was accompanied by increased leaf hydration, the probable outcome of increased root hydraulic conductance. Thereby, we tested the hypothesis that the ability of rhizobacterium (Bacillus subtilis IB22) to modify responses of plants to salt stress depends on abscisic acid (ABA) accumulating in roots.

Salt stress reduces root water uptake in barley (Hordeum vulgare L.) through modification of the transcellular transport path.

The aim of the study was to understand the hydraulic response to salt stress of the root system of the comparatively salt-tolerant crop barley (Hordeum vulgare L.). We focused on the transcellular path of water movement across the root cylinder that involves the crossing of membranes. This path allows for selective water uptake, while excluding salt ions. Hydroponically grown plants were exposed to 100 mM NaCl for 5-7 days and analysed when 15-17 days old. A range of complementary and novel approaches was used to determine hydraulic conductivity (Lp). This included analyses at cell, root and plant level and modelling of water flow. Apoplastic barrier formation and gene expression level of aquaporins (AQPs) was analysed. Salt stress reduced the Lp of root system through reducing water flow along the transcellular path. This involved changes in the activity and gene expression level of AQPs. Modelling of root-Lp showed that the reduction in root-Lp did not require added hydraulic resistances through apoplastic barriers at the endodermis. The bulk of data points to a near-perfect semi-permeability of roots of control plants (solute reflection coefficient σ ~1.0). Roots of salt-stressed plants are almost as semi-permeable (σ > 0.8).

Changes in soluble amino-N, soluble proteins and free amino acids in leaves and roots of salt-stressed maize genotypes

The effects of salt stress on the contents of organic solutes and on the pattern of free amino acids were studied in leaves and roots of two maize genotypes, BR5033 (salt-tolerant) and BR5011 (salt-sensitive). In leaves and roots of salt-stressed plants, soluble amino-N increased with time when compared to the controls. Salt stress increased the soluble protein content only in leaves of BR5011. Salinity increased the content of the majority of the free amino acids in leaves and roots of genotypes studied. Results suggest the hypothesis of disturbances in translocation of N-containing compounds from shoot to root in the salt-sensitive genotype. Results also suggest that the accumulation of organic solutes, mainly in roots of BR5033, may have an important role in the tolerance of this genotype to salt stress.

Effect of calcium on root development and root ion fluxes in salinised barley seedlings.

The effects of various Na / Ca ratios on root growth, development, and ion acquisition patterns were studied in hydroponic experiments with barley (Hordeum vulgare L.) plants. In total, interactions between three different levels of salinity (1, 50 and 100 mM NaCl) and three different levels of Ca2+ (0.1, 1 and 10 mM) were studied (a full factorial experiment). Growth rate and biomass accumulation were significantly lower in salinised roots. In addition to reduction in extension growth, salinity also significantly affected plant developmental processes (for example reduced root hair density and root thickening). Supplemental Ca2+ significantly ameliorated those detrimental effects of salinity. Non-invasive, microelectrode ion-flux (MIFE) measurements showed that the onset of salt stress caused rapid and prolonged efflux of H+, K+ and NH4+ from the root epidermis. This efflux could be significantly reversed, or completely prevented, by the presence of high Ca2+ concentration in the bath solution, even after several days of salt stress. Membrane potential measurements in root epidermal cells showed that high Ca2+ levels in the bath were able to restore (otherwise depolarised) membrane potential back to control level (-120 to -130 mV). At the same time, no significant impact of Ca2+ on net Na+ uptake in plant roots was found. Some limitations of the MIFE technique for study of Na+ uptake kinetics under saline conditions, as well as possible ionic mechanisms underlying the ameliorating Ca2+ effects on ion fluxes in roots of salt-stressed plants, are discussed.

Growth, mineral nutrition, organic constituents and rate of photosynthesis inSesbania grandiflora L. grown under saline conditions

Sesbania showed a luxuriant growth in soil with an electrical conductivity of up to 10 m Scm−1. Under saline conditions Na and Cl accumulated at different rates in the plants. Accumulation of these ions in the leaf rachis compared with leaflets appears to be an adaptive feature of this legume. Maintenance of an optimum K level and accumulation of Ca are also indicative of a salt-tolerance mechanism. Accumulation of Fe in the roots of salt-stressed plants is noteworthy. Organic acids and soluble sugars which accumulated in plants under stress condition may play a role in osmotic adjustment. The level of proline, however, remained unaltered. Though the chlorophyll content of the leaves decreased, the photosynthetic rate was found to be enhanced by saline conditions. The probable relationships between these changes and the salt tolerance mechanism in the plant have been discussed.