Influence of silicon on microdistribution of mineral ions in roots of salt-stressed barley as associated with salt tolerance in plants

Two contrasting barley (Hordeum vulgare L.) cultivars: Kepin No.7 (salt sensitive), and Jian 4 (salt tolerant) were grown hydroponically to investigate the microdistribution of mineral ions in roots as affected by silicon (Si) with respect to salt tolerance. The experiment was undertaken consisting of two treatments with 3 replicates: (i) 120 mmol · L⁻¹ NaCl alone (referred to as Si-NaCl+), (ii) 120 mmol · L⁻¹ NaCl + 1.0 mmol · L⁻¹ Si (as potassium silicate) (referred to as Si+NaCl+). Plant root tips were harvested for microanalysis using an energy dispersive X-ray microanalyzer (EDX) 30 d after transplanting. Higher Cl and Na X-ray peaks were recorded in the root epidermal, cortical and stelar cells of roots for the treatment Si-NaCl+ with the majorities of Na and Cl being accumulated in epidermal and cortical cells, while relatively low K peaks were observed regardless of the barley cultivars used. By contrast, considerably higher K peaks were detected in the epidermal, cortical and stelar cells of the roots for the treatment Si+NaCl+, but lower Cl and Na peaks were also observed for this treatment with both Na and Cl ions being evenly distributed in the epidermal, cortical and stelar cells. These findings directly support our previous finding, which showed that Si depressed the uptake of sodium but enhanced the uptake of potassium by salt-stressed barley. We believe that one of the possible mechanisms involved in Si-enhancement of salt tolerance in barley is attributed to the Si-induced changes in the uptake and microdistribution of mineral ions in plants.     

Influence of silicon on microdistribution of mineral ions in roots of salt-stressed barley as associated with salt tolerance in plants

Two contrasting barley (Hordeum vulgare L.) cultivars: Kepin No.7 (salt sensitive), and Jian 4 (salt tolerant) were grown hydroponically to investigate the microdistribution of mineral ions in roots as affected by silicon (Si) with respect to salt tolerance. The experiment was undertaken consisting of two treatments with 3 replicates: (i) 120 mmol · L-1 NaCl alone (referred to as Si-NaCl+), (ii) 120 mmol·L-1 NaCl + 1.0 mmol · L-1 Si (as potassium silicate) (referred to as Si+NaCl+). Plant root tips were harvested for microanalysis using an energy dispersive X-ray microanalyzer (EDX) 30 d after transplanting. Higher Cl and Na X-ray peaks were recorded in the root epidermal, cortical and stelar cells of roots for the treatment Si-NaCl+ with the majorities of Na and Cl being accumulated in epidermal and cortical cells, while relatively low K peaks were observed regardless of the barley cultivars used. By contrast, considerably higher K peaks were detected in the epidermal, cortical and stelar cells of th     

Characteristics of Salt-Tolerant and Salt-Susceptible Cultivars of Barley

Twelve cultivars of barley (Hordeum vulgare L.) from the collection of the Vavilov Institute of Plant Industry, Russian Academy of Agricultural Sciences, were screened by assessing the length of 6-day-old seedlings grown in water culture at 70, 120, and 170 mM NaCl. As a result, two salt-susceptible cultivars, Belogorskii and QB 60.1, and three salt-tolerant cultivars, Elo, Odesskii 115, and Local from Ecuador, were selected, and these cultivars were used in the greenhouse soil-culture experiments. The grain yield of salt-tolerant cultivars was affected by NaCl to a lesser degree than that of the salt-susceptible cultivars. In both cases, soil salinization increased the sodium content in the seedlings as compared to the control plants. Characteristically, salt-susceptible cultivars accumulated more Na⁺ in their shoots than salt-tolerant cultivars; the reciprocal pattern was found in the roots. Soil salinization decreased K⁺ content in the shoots of the salt-susceptible cv. Belogorskii as compared to the control, whereas in the most tolerant cv. Local from Ecuador, the potassium content increased.     

Corn uptake and microbial immobilization of 15N-labeled urea-N in soil as affected by composted pig manure

The tolerance of 24 genotypes of barley was assessed by estimating their survival in saline conditions either in a glasshouse or in a controlled environment cabinet. Two cultivars, sensitive Triumph and resistant Gerbel, were picked for further study, which involved sequential harvesting of plants grown in a range of salinities. After about one month in 200 mol m^–3 sodium chloride, the sodium concentration in the roots and shoots of the sensitive Triumph was about 1.5 times that in the roots of resistant Gerbel. The addition of Na to the root medium reduced the potassium transport to the shoot in Triumph to a much greater extent than in Gerbel, so the K:Na ratio of Gerbel was twice that for Triumph, when averaged over all treatments and harvests. The sodium, potassium and chloride concentrations within the major subcellular compartments of the cortical cells of roots of Triumph and Gerbel were determined by X-ray microanalysis following freeze-substitution and dry-sectioning. The mean cytoplasmic sodium concentration (245 mol m^–3 analysed volume) in Triumph grown in 200 mol m^–3 NaCl for 15 d was almost 1.4 times greater than that in the resistant Gerbel: the potassium concentration in Gerbel showed a lower reduction than did that of Triumph. Another major difference between the two cultivars was the higher concentrations of sodium and chloride in the cell walls of Triumph than Gerbel: the sodium concentration in the cortical cell walls of the salt-sensitive cultivar was about 1.75 times that in the more salt-resistant cultivar. The exchange capacity of the cell walls of Gerbel was greater than that of Triumph. We hypothesise that ion transport to the shoot reflects cytosolic ion concentrations, with a more sensitive cultivar having a higher sodium concentration in its cytoplasm than a more resistant variety. It is noteworthy that the difference in the K:Na ratio between the shoots of Gerbel and Triumph after 15 days of exposure to 200 mol m^–3 NaCl was similar to the difference in their symplastic K:Na ratios.     

New perspective on the mechanism of alleviating salt stress by spermidine in barley seedlings

Salt stress is considered to be a major limiting factor for plant growth and crop productivity. Salt injuries in plants are mostly due to excess Na⁺ entry. A possible survival strategy of plants under saline environments is the effective compartmentation of excess Na⁺ by sequestering Na⁺ in roots and inhibiting transport of Na⁺ from roots to shoots. Our previous study showed that exogenous application of polyamines (PAs) could attenuate salt injuries in barley plants. In order to further understand such protective roles of PAs against salt stress, the effects of spermidine (Spd) on sodium and potassium distribution in barley (Hordeum vulgare L.) seedlings under saline conditions were investigated. The results showed that exogenous application of Spd induced reductions in Na⁺ levels in roots and shoots with comparison of NaCl-treated plants, while no significant changes in K⁺ levels were observed. Correspondingly, the plants treated with Spd exogenously maintained high values of [K⁺]/[Na⁺] as compared with salt-stressed plants. Moreover, it was shown by X-ray microanalysis that K⁺ and Na⁺ accumulated mainly in the exodermal intercellular space and cortical cells of roots under salinity stress, and low accumulation was observed in endodermal cells and stelar parenchyma, indicating Casparian bands possibly act as ion transport barriers. Most importantly, Spd treatment further strengthened this barrier effects, leading to inhibition of Na⁺ transport into shoots. These results suggest that, by reinforcing barrier effects of Casparian bands, exogenous Spd inhibits Na⁺ transport from roots to shoots under conditions of high salinity which are beneficial for attenuating salt injuries in barley seedlings.     

Exogenous silicon (Si) increases antioxidant enzyme activity and reduces lipid peroxidation in roots of salt-stressed barley (Hordeum vulgare L.)

Two contrasting barley (Hordeum vulgare L.) cultivars, i.e. Kepin No.7 (salt sensitive) and Jian 4 (salt tolerant), were grown hydroponically to study the effect of exogenous silicon (Si) on time dependent changes of the activities of major antioxidant enzymes and of lipid peroxidation in roots under salt stress. Enzymes included: superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and glutathione reductase (GR). Three treatments with three replicates were investigated consisting of a control (basal nutrients with neither NaCl nor Si added), 120 mmol/L-1 NaCl, and 120 mmol/L-1 NaCl +1.0 mmol/L-1 Si. Plant roots were harvested 2, 4 and 6 days after treatment and assayed for activities of the antioxidant enzymes and the concentrations of reduced glutathione (GSH) and malondialdehyde (MDA), and electrolytic leakage percentage (ELP). The activities of SOD, POD and CAT in roots of salt-stressed plants were significantly stimulated at Day 2 compared to control plants, but considerably decreased at Day 4 and onward. GR activity in roots of salt-stressed plants remained unchanged at Day 2, but significantly decreased at Day 4 and onward. However, exogenous Si significantly enhanced these enzyme activities in roots of salt-stressed plants compared to Si-deprived salt treatments. This Si effect was time-dependent and became stronger as the experiments continued. The tendency of change in the activities of antioxidant enzymes and the concentration of GSH coincided with the concentration of MDA, the end product of lipid peroxidation, and the ELP. Higher activities of antioxidant enzymes, and higher concentration of GSH, but lower concentration of MDA and lower ELP were noted in cultivar Jian 4 compared to Kepin No. 7, implying genotypic differences with Jian 4 being less susceptible to stress-dependent membrane lipid peroxidation. The effects of Si-enhanced salt tolerance are discussed with respect to cell membrane integrity, stability and function in barley.     

Salt-tolerant reed plants contain lower Na<Superscript>+</Superscript> and higher K<Superscript>+</Superscript> than salt-sensitive reed plants

Reed plants (Phragmites australis Trinius) grow not only in fresh and brackish water areas but also in arid and high salinity regions. Reed plants obtained from a riverside (Utsunomiya) were damaged by 257 mM NaCl, whereas desert plants (Nanpi) were not. When the plants were grown under salt stress, the shoots of the Utsunomiya plants contained high levels of sodium and low levels of potassium, whereas the upper part of the Nanpi plants contained low levels of sodium and high levels of potassium. One month salt stress did not affect potassium contents in either Utsunomiya or Nanpi plants, but it did dramatically increase sodium contents only in the Utsunomiya plants. The ratio of K⁺ to Na⁺ was maintained at a high level in the upper parts of the Nanpi plants, whereas the ratio markedly decreased in the Utsunomiya plants in the presence of NaCl. Accumulation of Na⁺ in the roots and Na⁺ efflux from the roots were greater in the Nanpi plants than in the Utsunomiya plants. These results suggest that the salt tolerance mechanisms of Nanpi reed plants include an improved ability to take up K⁺ to prevent an influx of Na⁺ and an improved ability to exclude Na⁺ from the roots.     

Potato plants bearing a vacuolar Na<Superscript>+</Superscript>/H<Superscript>+</Superscript> antiporter HvNHX2 from barley are characterized by improved salt tolerance

Two cultivars of potato (Solanum tuberosum L.) were transformed with a barley antiporter gene HvNHX2 driven by the CaMV 35S promoter. The expressed transgene conferred a higher NaCl tolerance to one of the cultivars. Under salt stress, the more salt-tolerant transgenic plants had longer roots, higher dry weight, and suppressed cell expansion as compared to wild-type plants. The salt tolerance of the plants grown in vitro was not accompanied by elevated total sodium in any plant organs tested. Instead, higher potassium was found in roots of transgenic plants. Possible mechanisms of plant salt tolerance are discussed.     

Response of barley grains to the interactive e.ect of salinity and salicylic acid

Effect of grain soaking presowing in 1 mM salicylic acid (SA) and NaCl (0, 50, 100, 150 and 200 mM) on barley (Hordeum vulgare cv Gerbel) was studied. Increasing of NaCl level reduced the germination percentage, the growth parameters (fresh and dry weight), potassium, calcium, phosphorus and insoluble sugars content in both shoots and roots of 15-day old seedlings. Leaf relative water content (RWC) and the photosynthetic pigments (Chl a, b and carotenoids) contents also decreased with increasing NaCl concentration. On the other hand, Na, soluble sugars, soluble proteins, free amino acids including proline content and lipid peroxidation level and peroxidase activity were increased in the two plant organs with increasing of NaCl level. Electrolyte leakage from plant leaves was found to increase with salinity level. SA-pretreatment increased the RWC, fresh and dry weights, water, photosynthetic pigments, insolube saccharides, phosphorus content and peroxidase activity in the stressed seedlings. On the contrary, Na⁺, soluble proteins content, lipid peroxidation level, electrolyte leakage were markedly reduced under salt stress with SA than without. Under stress conditions, SA-pretreated plants exhibited less Ca²⁺ and more accumulation of K⁺, and soluble sugars in roots at the expense of these contents in the plant shoots. Exogenous application (Grain soaking presowing) of SA appeared to induce preadaptive response to salt stress leading to promoting protective reactions to the photosynthetic pigments and maintain the membranes integrity in barley plants, which reflected in improving the plant growth.     

HCO−3 uptake through the roots and its effect on the productivity of willow cuttings

Abstract Young willow plants (Salix‘aquatica gigantea’) were grown in hydroponic culture media, and ¹⁴C–labelled sodium bicarbonate was fed to the roots. Uptake of ¹⁴C-label in the leaves and shoots was assayed after two different feeding periods (6 h, 48 h). Even during the shortest feeding period, ¹⁴C-label had been transferred to the leaves and shoots. Compared with the longer feeding period, after the 6 h feeding period more label was in the form of acid-labile products, whereas after the 48 h feeding period most of the label was in acid-stable products. A second experiment was designed to test whether carbon uptake by roots affects the growth of young willow plants. Uniform rooted cuttings were grown in hydroponic cultures at five different levels of bicarbonate: 0, 0.015, 0.147 0.737, and 1.473 mol m^?3 NaHCO₃. After a 4-week growing period we determined the biomass of leaves, shoots, roots and cuttings. Production of total dry matter (shoots, leaves and roots) increased with increasing bicarbonate concentration. Saturation of dry matter production was reached at 0.737 mol m^?3 NaHCO₃, but a higher concentration of NaHCO₃ (1.470 mol m^?3) caused a slight decrease in the dry matter production. At 0.737 mol m^?3 NaHCO₃ the total dry weight increased by 31.1%, which suggests that uptake of dissolved carbon dioxide through the roots might affect carbon budgeting in young willow plants.