Seasonal changes in the germination responses of Hordeum maritimum and H. murinum seeds in relation to salinity,temperature and after‐ripening time

Abstract

The effects of temperature and salinity (NaCl) on germination of Hordeum maritimum With, (halophyte) and H. murinum L. (glycophyte) seeds were investigated. Dehulled caryopses were used for monthly germination trials, starting from November (120 days of after‐ripening in darkness at 20±1°C). Trials were continued for one year. Differences in germination response between the two species were observed, confirming that H. Maritimum is better adapted to high salinity levels and to variations in external temperature than H. murinum. H. maritimum showed a germination control mechanism related to after‐ripening time and based on seed dormancy break/resumption. At higher temperature (30°C), thermodormancy was also recorded. No germination strategies were observed in H. murinum that is relatively insensitive to the combined effects of temperature and salinity. Thus, in virtually all treatments, H. murinum exhibited a higher germination rate compared with H. maritimum, as early as 72 h after imbibition, suggesting that dormancy, both in the presence or absence of salt, is totally abolished by early fall or at the latest in winter.     

Differences in efficient metabolite management and nutrient metabolic regulation between wild and cultivated barley grown at high salinity

Physiological and biochemical responses of Hordeum maritimum and H. vulgare to salt stress were studied over a 60‐h period. Growth at increasing salinity levels (0, 100, 200 and 300 mM NaCl) was assessed in hydroponic culture. H. maritimum was shown to be a true halophyte via its typical behaviour at high salinity. Shoot growth of cultivated barley was gradually reduced with increasing salinity, whereas that of wild barley was enhanced at 100 and 200 mm NaCl then slightly reduced at 300 mM NaCl. The higher salt tolerance of H. maritimum as compared to H. vulgare was due to its higher capacity to maintain cell turgor under severe salinity. Furthermore, H. maritimum exhibited fine regulation of Na⁺ transport from roots to shoots and, unlike H. vulgare, it accumulated less Na⁺ in shoots than in roots. In addition, H. maritimum can accumulate more Na⁺ than K⁺ in both roots and shoots without the appearance of toxicity symptoms, indicating that Na⁺ was well compartmentalized within cells and substituted K⁺ in osmotic adjustment. The higher degree of salt tolerance of H. maritimum is further demonstrated by its economic strategy: at moderate salt treatment (100 mm NaCl), it used inorganic solutes (such as Na⁺) for osmotic adjustment and kept organic solutes and a large part of the K⁺ for metabolic activities. Indeed, K⁺ use efficiency in H. maritimum was about twofold that in H. vulgare; the former started to use organic solutes as osmotica only at high salinity (200 and 300 mm NaCl). These results suggest that the differences in salt tolerance between H. maritimum and H. vulgare are partly due to (i) differences in control of Na⁺ transport from roots to shoots, and (ii) H. maritimum uses Na⁺ as an osmoticum instead of K⁺ and organic solutes. These factors are differently reflected in growth.     

Assessing the role of endophytic bacteria in the halophyte Arthrocnemum macrostachyum salt tolerance

• There is an increasing interest to use halophytes for revegetation of salt affected ecosystems, as well as in understanding their mechanisms of salt tolerance. We hypothesized that bacteria from the phyllosphere of these plants might play a key role in its high tolerance to excessive salinity.
• Eight endophytic bacteria belonging to Bacillus and closely related genera were isolated from phyllosphere of the halophyte Arthrocnemum macrostachyum growing in salty agricultural soils. The presence of plant‐growth promoting (PGP) properties, enzymatic activities and tolerance towards NaCl was determined. Effects of inoculation on seeds germination and adult plant growth under experimental NaCl treatments (0, 510 and 1030 mM NaCl) were studied.
• Inoculation with a consortium including the best performing bacteria improved considerably the kinetics of germination and the final germination percentage of A. macrostachyum seeds. At high NaCl concentrations (1030 mM), inoculation of plants mitigated the effects of high salinity on plant growth and physiological performance and, in addition, this consortium appears to have increased the potential of A. macrostachyum to accumulate Na⁺ in its shoots, thus improving sodium phytoextraction capacity.
• Bacteria isolated from A. macrostachyum phyllosphere seem to play an important role in plant salt tolerance under stressing salt concentrations. The combined use of A. macrostachyum and its microbiome can be an adequate tool to enhance plant adaptation and sodium phytoextraction during restoration of salt degraded soils.

     

Effect of Salinity on Seed Germination,Growth, and Ion Accumulation of Atriplex patula (Chenopodiaceae)

Seeds and seedlings of the halophyte Atriplex patula were exposed to 0–2% NaCl to determine the effect of salt stress on germination and growth. Seeds germinated and plants survived and grew in solutions of up to 2.0% NaCl. Both seed germination and dry mass production were negatively affected by increased salinity. Dry mass production declined to 1% of controls and seed germination to 17% of controls in the 2% NaCl treatments, indicating that seeds were less inhibited than growing plants. Also, recovery treatments indicated that high salinity did not permanently injure seeds. Percent ash, and Na⁺ and Cl⁻ ions increased in shoots with each salt increment, while the K⁺ ion content decreased sharply. Atriplex patula is a facultative halophyte, and is limited to low and moderately saline sites because both seed germination and growth are severely reduced at salinities > 1% NaCl.     

Molecular cloning and characterization of plasma membrane- and vacuolar-type Na+/H+ antiporters of an alkaline-salt-tolerant monocot, Puccinellia tenuiflora

A better understanding of salt tolerance in plants might lead to the genetic engineering of crops that can grow in saline soils. Here we cloned and characterized plasma membrane and vacuolar Na?/H? antiporters of a monocotyledonous alkaline-tolerant halophyte, Puccinellia tenuiflora. The predicted amino acid sequence of the transporters were very similar to those of orthologs in monocotyledonous crops. Expression analysis showed that (1) NHA was more strongly induced by NaCl in the roots of P. tenuiflora while in rice it was rather induced in the shoots, suggesting that the role of NHA in salt excretion from the roots partly accounts for the difference in the tolerance of the two species, and that (2) NHXs were specifically induced by NaHCO? but not by NaCl in the roots of both species, suggesting that vacuolar-type Na?/H? antiporters play roles in pH regulation under alkaline salt conditions. Overexpression of the antiporters resulted in increased tolerance of shoots to NaCl and roots to NaHCO?. Overexpression lines exhibited a lower Na? content and a higher K? content in shoots under NaCl treatments, leading to a higher Na?/H? ratio.     

ABA, GA3, and nitrate may control seed germination of Crithmum maritimum (Apiaceae) under saline conditions

Impaired germination is common among halophyte seeds exposed to salt stress, partly resulting from the salt-induced reduction of the growth regulator contents in seeds. Thus, the understanding of hormonal regulation during the germination process is a main key: (i) to overcome the mechanisms by which NaCl-salinity inhibit germination; and (ii) to improve the germination of these species when challenged with NaCl. In the present investigation, the effects of ABA, GA₃, NO⁻₃, and NH⁺₄ on the germination of the oilseed halophyte Crithmum maritimum (Apiaceae) were assessed under NaCl-salinity (up to 200 mM NaCl). Seeds were collected from Tabarka rocky coasts (N-W of Tunisia). The exogenous application of GA₃, nitrate (either as NaNO₃ or KNO₃), and NH₄Cl enhanced germination under NaCl salinity. The beneficial impact of KNO₃ on germination upon seed exposure to NaCl salinity was rather due to NO⁻₃ than to K⁺, since KCl failed to significantly stimulate germination. Under optimal conditions for germination (0 mM NaCl), ABA inhibited germination over time in a dose dependent manner, but KNO₃ completely restored the germination parameters. Under NaCl salinity, the application of fluridone (FLU) an inhibitor of ABA biosynthesis, stimulated substantially seed germination. Taken together, our results point out that NO⁻₃ and GA₃ mitigate the NaCl-induced reduction of seed germination, and that NO⁻₃ counteracts the inhibitory effect of ABA on germination of C. maritimum. To cite this article: A. Atia et al., C. R. Biologies 332 (2009).     

Identification of proteins associated with ion homeostasis and salt tolerance in barley

Identification and characterization of proteins involved in salt tolerance are imperative for revealing its genetic mechanisms. In this study, ionic and proteomic responses of a Tibetan wild barley XZ16 and a well‐known salt‐tolerant barley cv. CM72 were analyzed using inductively coupled plasma‐optical emission spectrometer, 2DE, and MALDI‐TOF/TOF MS techniques to determine salt‐induced differences in element and protein profiles between the two genotypes. In total, 41 differentially expressed proteins were identified in roots and leaves, and they were associated with ion homeostasis, cell redox homeostasis, metabolic process, and photosynthesis. Under salinity stress, calmodulin, Na/K transporters, and H⁺‐ATPases were involved in establishment of ion homeostasis for barley plants. Moreover, ribulose‐1,5‐bisphosphate carboxylase/oxygenase activase and oxygen‐evolving enhancer proteins were significantly upregulated under salinity stress, indicating the great impact of salinity on photosynthesis. In comparison with CM72, XZ16 had greater relative dry weight and lower Na accumulation in the shoots under salinity stress. A higher expression of HvNHX1 in the roots, and some specific proteins responsible for ion homeostasis and cell redox homeostasis, was also found in XZ16 exposed to salt stress. The current results showed that Tibetan wild barley XZ16 and cultivated barley cultivar CM72 differ in the mechanism of salt tolerance.     

Vegetative salt tolerance of barnyard grass mutants selected for salt tolerant germination

Improving salt tolerance of economically important plants is imperative to cope with the increasing soil salinity in many parts of the world. Mutation breeding has been widely used to improve plant performance under salinity stress. In this study, we have mutagenized Echinochloa crusgalli L. with sodium azide and three selected mutants (designated fows A) with salt tolerant germination. Their vegetative growth was compared to that of the wild type after short-term and long-term salt stress. The germination of the three fows A mutants in the presence of inhibitory concentrations of NaCl, KCL, and mannitol was better than that of the wild type. Early growth of the mutants in the presence of 200 mM NaCl was also better than that of the wild type perhaps due to improved K⁺ uptake and enhanced accumulation of sugars particularly sucrose at least in two mutants. But the three mutants and the wild type responded similarly to long-term salt stress. The tolerance mechanisms during short-term and long-term salt stress are discussed.     

Comparative Study of the Interactive Effects of Salinity and Phosphorus Availability in Wild (Hordeum maritimum) and Cultivated Barley (H. vulgare)

The present study aimed to compare the effects of phosphorus (P) deficiency applied only or combined with salinity on root response, P partitioning, acid phosphatase activity, and phenolic compounds in wild (Hordeum maritimum) and cultivated (H. vulgare) barley species. Seedlings were grown hydroponically under low or sufficient P supply, with or without 100 mM NaCl for 55 days. Results showed that, when individually applied, P deficiency and salinity restricted the whole plant relative growth rate in both species of barley, with a more pronounced impact of the former stress. These depressive effects were more pronounced in H. vulgare than in H. maritimum. The combined effects of P deficiency and salinity were not additive neither on whole plant RGR nor on root response parameters in both species. The root area, root/shoot P content, root and leaf acid phosphatase activities, and shoot flavonoids contents increased under P deficiency conditions with and without salt in both species. Overall, the relatively better tolerance of H. maritimum plants to P deficiency applied only or combined with salinity could be explained by the capacity of this species to maintain higher P acquisition efficiency in concomitance with a larger root system, a higher root/shoot DW ratio, a higher root/shoot P content, a greater root and leaf acid phosphatase activities, and a higher flavonoid content and antioxidant capacity under combined effects of both stresses. Thus, H. maritimum constitutes a promising model to ameliorate the tolerance of the cultivated barley species under low-P soils and/or saline regions.     

Effects of temperature,salinity and cold stratification on seed germination in halophytes

Salt tolerance of halophytes corresponds with the habitat requirement of the species. It is an important factor during the germination phase and it can determine successful establishment. This paper presents the effects of alternating temperature–light regimes (4/8°C, 10/20°C, 20/32°C; 12 h dark: 12 h light) and different salinity levels (0, 200, 400, 600 mmol l²¹ NaCl) on seed germination of five halophytes, Halimione pedunculata, Bupleurum tenuissimum, Aster tripolium, Triglochin maritimum and Armeria maritima. The five species differ with respect to family and life‐form and spatially correspond to a decreasing salt gradient (i.e. distance from salt water, with H. pedunculata being the most tolerant and A. maritima being the least). Armeria maritima, A. tripolium and T. maritimum seeds were additionally subjected to a cold stratification experiment. The results showed that Halimione pedunculata, an annual therophyte of year‐round heavily saline habitats, was dormant under all experimental conditions. Bupleurum tenuissimum, a species typical to sites of varying salinity prone to leaching during spring and autumn rainfall, germinated best under cold and warm temperatures, but only under non‐saline conditions. Aster tripolium and T. maritimum, close neighbours in salt marshes, showed very similar germination behaviour: seeds of both species tolerated high levels of salinity and germinated best in summer temperatures during periods of highest soil salinity, and germination was significantly promoted by cold. Armeria maritima, a species usually found on the marginal fringes of saline habitats, germinated only under low salt levels and maximum germination was under cold (spring) and warm (autumn) temperatures, with no significant effect of cold stratification.     

Effect of salinity and chemical factors on seed germination in the halophyte Crithmum maritimum L.

Seeds of the halophyte Crithmum maritimum L. were exposed to salt stress and chemical pretreatments in order to improve germination. Seeds submitted to salt stress did not germinate but they recovered rapidly upon transfer to distilled water, recovery being higher after a low salinity pretreatment. Chemical treatments resulted in differential effects on seed germination. Known dormancy breakers such as potassium nitrate and thiourea had no effect on sea fennel seed germination. Conversely, l-ascorbic acid (40 or 60 mM) and ethanol (96%) significantly improved germination rate by 10, 30 and 30%, respectively. Pretreatment of seeds with l-ascorbic acid at 40 mM was shown to alleviate the negative effects of low NaCl concentration on germination. These findings indicate that the application of ascorbic acid may be used to improve sea fennel seed germination, which is of great interest for cultivating this plant.     

FACTORS INFLUENCING SEED GERMINATION IN SALICORNIA PACIFICA VAR. UTAHENSIS

The halophyte, Salicornia pacifica var. utahensis (Tiderstorm) Munz produces seed under high salinity conditions, and deposits its seed on saline soil. Experiments were conducted to determine the effect of salinity, temperature and growth regulators on germination. Results indicate that the seeds can germinate at very high salt concentration (5% NaCl). Germination was sensitive to the changes in temperature regimes. At higher 30–20 C, light-dark sequence, no germination occurred at 3, 4 and 5% NaCl treatments. On the other hand, 30% germination did occur at 5% NaCl treatment at a temperature regime of 15–5 C. These seeds required light for germination. Only 50% germination occurred in the non-saline control in the dark and the addition of NaCl further reduced germination. The GA₃ partially alleviated the inhibitory effect of NaCl and darkness. Kinetin did not promote germination.     

Effect of oxygen availability and salinity on EARLY LIFE HISTORY STAGES OF SALT MARSH PLANTS. I. Different germination strategies of Spartina alterniflora and Phragmites australis (Poaceae)

Gradients in oxygen availability and salinity are among the most important environmental parameters influencing zonation in salt marsh communities. The combined effects of oxygen and salinity on the germination of two salt marsh grasses, Spartina alterniflora and Phragmites australis, were studied in growth chamber experiments. Germination of both species was initiated by emergence of the shoot and completed by root emergence. Percentage S. alterniflora germination was reduced at high salinity (40 g NaCl/L) and in decreased oxygen (5 and 2.5%). In 0% oxygen shoots emerged, but roots did not. P. australis germination was reduced at a lower salinity (25 g NaCl/L) than S. alterniflora, and inhibited at 40 g NaCl/L and in anoxia. However, a combination of hypoxia (10 and 5% O2) and moderate salinity (5 and 10 g NaCl/L) increased P. australis germination. When bare areas in the salt marsh are colonized, the different germination responses of these two species to combinations of oxygen and salt concentrations are important in establishing their initial zonation. In high salinity wetlands S. alterniflora populates the lower marsh and P. australis occupies the high marsh at the upland boundary.     

The effect of extended exposure to hypersaline conditions on the germination of five inland halophyte species

In order to determine how salinity and exposure time affect seed viability and germination, seeds of five halophytes, Atriplex prostrata, Hordeum jubatum, Salicornia europaea, Spergularia marina, and Suaeda calceoliformis were exposed to 3.0, 5.0, and 10.0% NaCl solutions for 30, 60, 90, 365, and 730 d. Recovery experiments in distilled water indicated significantly different species responses to salinity over time. Percentage germination and rate of germination in H. jubatum were dramatically reduced following extended exposure and all seeds exposed to 10% NaCl for > 1 yr failed to germinate. Spergularia marina seeds were stimulated following short-term exposure to 3% NaCl; however, germination was delayed and overall germination was significantly reduced with exposure time in the two higher salinity levels. Percentage germination in A. prostrata decreased over time, but salinity level was not related to this reduction. Germination of S. europaea and S. calceoliformis, the most salt-tolerant species being tested, was stimulated by exposure to high salinity. Both species had a significant increase in percentage germination and in the germination rate when compared to seeds germinated in distilled water. Baseline germination data from seeds placed in 0, 1, 2, and 3% NaCl solutions indicated that S. europaea and S. calceoliformis were the only species to germinate in the 3% NaCl solution. Spergularia marina failed to germinate in the 2% NaCl treatment, and germination of A. prostrata and H. jubatum was significantly reduced at this salinity level. It is concluded that prolonged exposure to saline solutions can inhibit or stimulate germination in certain species, and the resulting germination and recovery responses are related to the duration and intensity of their exposure to salt in their natural habitats.     

Influence of Salinity and Temperature on the Germination of Haloxylon recurvum Bunge ex. Boiss.

The stem succulent perennial halophyteHaloxylon recurvum Bungeex. Boiss. grows and produces seed under highly saline conditionsand seeds are deposited in saline soils. Experiments were conductedto determine the effect of salinity and temperature on the germinationof seeds. Results indicate that seeds can germinate at veryhigh salt concentrations (500 mM). However, highest germinationpercentages were obtained in distilled water. Cooler thermoperiodspromoted germination, while high temperatures significantlyinhibited the germination of seeds at all NaCl concentrationstested. Rate of germination decreased with increases in salinity.At higher thermoperiods the rate of germination was significantlylower in comparison to lower thermoperiods. Seeds recover afterbeing transferred to distilled water and recovery was higherfrom higher salinity concentrations and lower thermoperiods.Final recovery germination percentages in high salt treatmentswere significantly lower than non-saline controls, indicatingthat exposure to high concentration of NaCl permanently inhibitedgermination. Germination; halophyte; Haloxylon recurvum recovery of germination; salinity; temperature     

Comparative salt tolerance analysis between Arabidopsis thaliana and Thellungiella halophila, with special emphasis on K(+)/Na(+) selectivity and proline accumulation

The eco-physiology of salt tolerance, with an emphasis on K⁺ nutrition and proline accumulation, was investigated in the halophyte Thellungiella halophila and in both wild type and eskimo-1 mutant of the glycophyte Arabidopsis thaliana, which differ in their proline accumulation capacity. Plants cultivated in inert sand were challenged for 3 weeks with up to 500 mM NaCl. Low salinity significantly decreased A. thaliana growth, whereas growth restriction was significant only at salt concentrations equal to or exceeding 300 mM NaCl in T. halophila. Na⁺ content generally increased with the amount of salt added in the culture medium in both species, but T. halophila showed an ability to control Na⁺ accumulation in shoots. The analysis of the relationship between water and Na⁺ contents suggested an apoplastic sodium accumulation in both species; this trait was more pronounced in A. thaliana than in T. halophila. The better NaCl tolerance in the latter was associated with a better K⁺ supply, resulting in higher K⁺/Na⁺ ratios. It was also noteworthy that, despite highly accumulating proline, the A. thaliana eskimo-1 mutant was the most salt-sensitive species. Taken together, our findings indicate that salt tolerance may be partly linked to the plants’ ability to control Na⁺ influx and to ensure appropriate K⁺ nutrition, but is not linked to proline accumulation.     

Comparison of salt tolerance and osmotic adjustment of low-sodium and high-sodium subspecies of the C4 halophyte, Atriplex canescens

The relationship between Na⁺ accumulation and salt tolerance was tested by comparing subspecies of the halophyte, Atriplex canescens (fourwing saltbush), that differed markedly in Na⁺ content and Na:K ratios. Above ground tissues of one low-sodium and two high-sodium subspecies were compared with respect to cation accumulation, osmotic adjustment and growth along a salinity gradient in greenhouse trials. Plants of each subspecies were grown for 80 d on 2.2, 180, 540 and 720 mol m^?3 NaCl. At harvest, A. canescens ssp. canescens had significantly lower Na⁺ levels, higher K⁺ levels and lower Na:K ratios in leaf and stem tissues than A. canescens ssp. macropoda and linearis over the salinity range (P < 0.05 or 0.01). Na:K ratios in leaves of the latter two, high-sodium, subspecies were approximately 2 on the lowest salinity treatment and ranged from 5 to 10 on the more saline solutions. By contrast, Na:K ratios in leaves of the low-sodium subspecies canescens, were only 0.4 on the lowest salinity and ranged narrowly from 1.7 to 2.3 at higher salinities. However, despite different patterns of Na⁺ and K⁺ accumulation, all three subspecies exhibited equally high salt tolerance and had similar osmotic pressures in their leaves or stems over the salinity range. Contrary to expectations, high salt tolerance was not necessarily dependent on high levels of Na⁺ accumulation in this species.     

Effect of salinity on seed germination and seedling growth of the halophyte Suaeda japonica Makino

Seed germination and seedling growth of the annual halophyte species Suaeda japonica Makino were investigated in response to variable salinity of sediment pore water. The germination percentage of S. japonica’s soft brown seeds, which are dominant among dimorphic seeds, decreased with an increase in salinity, although germination was still observed at 1200‐mM NaCl concentration. The germination percentage and germination speed observed in April were higher than those observed in December when treated with sediment water with 400–1200 mM of NaCl concentrations. These data suggest that S. japonica seedlings could be established on sediments that experience high temperatures. Germination recovery of S. japonica seeds transferred from 600‐mM NaCl containing sediment (seawater equivalent) was lowest among 0–1200‐mM NaCl treatments, implying the low tolerance of seawater conditions of S. japonica seeds. Seeds germinated in 900‐ to 1200‐mM NaCl medium showed poor growth, but survived, in hypersaline conditions, and exhibited improvement in growth upon transfer to lower salinity.