Salinity effect on plant growth and leaf demography of the mangrove, Avicennia germinans L.

We assessed the effect of salinity on plant growth and leaf expansion rates, as well as the leaf life span and the dynamics of leaf production and mortality in seedlings of Avicennia germinans L. grown at 0, 170, 430, 680, and 940 mol m⁻³ NaCl. The relative growth rates (RGR) after 27 weeks reached a maximum (10.4 mg g⁻¹ d⁻¹) in 170 mol m⁻³ NaCl and decreased by 47 and 44% in plants grown at 680 and 940 mol m⁻³ NaCl. The relative leaf expansion rate (RLER) was maximal at 170 mol m⁻³ NaCl (120 cm m⁻² d⁻¹) and decreased by 57 and 52% in plants grown at 680 and 940 mol m⁻³ NaCl, respectively. In the same manner as RGR and RLER, the leaf production (P) and leaf death (D) decreased in 81 and 67% when salinity increased from 170 to 940 mol m⁻³ NaCl, respectively. Since the decrease in P with salinity was more pronounced than the decrease in D, the net accumulation of leaves per plant decreased with salinity. Additionally, an evident increase in annual mortality rates (λ) and death probability was observed with salinity. Leaf half-life (t _0.5) was 425 days in plants grown at 0 mol m⁻³ NaCl, and decreased to 75 days at 940 mol m⁻³ NaCl. Thus, increasing salinity caused an increase in mortality rate whereas production of new leaves and leaf longevity decreased and, finally, the leaf area was reduced.     

Salt-tolerance in plants. II. In vitro translation of m-RNAs from salt-tolerant and salt-sensitive plants on wheat germ ribosomes. Responses to ions and compatible organic solutes

Abstract Messenger RNA from salt-sensitive and salt-tolerant plants Triticum aestivum. Beta vulgaris, Pisum sativum, Chenopodium album and Atriplex nummularia was translated in vitro in a wheatgerm translation system. The optimal monovalent and divalent ion concentrations for translation were independent of the salt tolerance of the plants from which the m-RNAs were derived. Translation was optimal in 100 120 mol m⁻³ potassium acetate and 1.5–2.0 mol m⁻³ Mg²⁺. Substitution of Na⁺ for K⁺, or of Cl⁻ for acetate, was inhibitory. The pattern of polypeptides synthesized from cytoplasmic m-RNAs of salt-sensitive and salt-tolerant plants remained constant in all the conditions examined. The effects of adding the ‘compatible' organic solutes glycine-betaine and mannitol were examined in the wheat-germ system primed with RNA from the leaves of Triticum aestivum or Beta vulgaris. The rate of translation, the optimum ionic concentrations and the distribution of polypeptide products were maintained in organic solute concentrations of up to 500 mol m⁻³. Proline above 300 mol m⁻³ and surcose above 100 mol m⁻³ did inhibit translation. The results indicate that translation in plants is unlikely in cytoplasmic K⁺ concentrations exceeding 180 mol m⁻³, but would proceed in the presence of up to 500 mol m⁻³ mannitol or glyinebetaine, or of up to 300 mol m⁻³ proline.     

Effect of Ca2+ on the retention of glycerol and amino acids in Dunaliella tertiolecta

When D. tertiolecta cells, previously incubated in a 0.5 kmol m⁻³ NaCl medium with 1mol m⁻³ Ca²⁺, were transferred to an isotonic NaCl medium without Ca²⁺, the intracellular glycerol, as well as intracellular amino acids, was transiently lost to the medium within 30 min. The transient leakage of glycerol and amino acids was enhanced by the addition of EGTA (1 mol m⁻³), while the addition of SrCl₂ (1 mol m ⁻³) or polyamines such as spermidine (5 mol m⁻³) and spermine (5 mol m⁻³) restrained the leakage caused by the lack of external Ca²⁺ of intracellular glycerol and amino acids.     

Salt-tolerance in plants. I. Ions, compatible organic solutes and the stability of plant ribosomes

Abstract Polysomes and ribosomes recovered from a number of plant species were tested for stability when incubated at 25°C in salt solutions in the absence of ATP and initiation factors. Stability was assessed by sucrose density gradient analysis. The stability was inversely proportional to salt concentrations above 125 mol m⁻³ KCl. Polysomes were less stable in the presence of Na⁺ than K⁺ salts, and were much less stable in Cl⁻ than in acetate salts. Polysomes from Triticum aestivum. Hordeum vulgare, Capsicum annuum, Helianthus annuus. Pisum sativum, Atriplex nummularia, Beta vulgaris, Cladophora sp., Enteromorpha sp. and Corallina cuvieri were similarly sensitive to KCl. Polysomes from Ulva lactuca were more sensitive than the other species. Cytoplasmic and plastid polysomes from T. aestivum were similarly unstable in 500 mol m⁻³ KCl. Unprogrammed ribosomal subunit couples from T. aestivum, B. vulgaris and U. lactuca showed Mg²⁺-dependent conformational instability and dissociation in KCl. Slight differences in ribosomal stability were observed between species, but these were unrelated to the salt tolerances of the plants. The ‘compatible’ organic solutes, glycinebetaine and proline, failed to reduce ion-induced instability. Ribosome yield and polysome profiles were similar in leaves of B. vulgaris containing significantly different levels of both Na⁺ and Cl⁻ after growth in media containing 50 or 200 mol m⁻³ NaCl. The results are consistent with the hypothesis that plants maintain a cytoplasmic solute environment that is compatible with ribosomal stability.     

Leaf expansion in sunflower as influenced by salinity and short-term changes in carbon fixation

Abstract With a view to defining factors regulating the growth responses of sunflower to salinity, plants were grown in solution culture (0, 50 or 100 mol m⁻³ NaCl) and under natural light, and the areas of every leaf measured once or twice daily from 22 until 38 d after germination. During this period, carbon availability for growth was manipulated by changing light levels and by the use of a photosynthesis inhibitor, DCMU. Salinity reduced relative leaf expansion rates per plant (RLER) by an average of 0.04 (50 mol m⁻³) and 0.08 (100 mol m⁻³) m² m⁻² d⁻¹ compared with control plants of equivalent leaf area: the effects were found in expanding leaves regardless of age or size. Control plants expanded faster during the day than the night, but plants grown in salt had an almost constant RLER throughout the 24 h, indicating that salt influences the rate of utilization of assimilates independently of their production. DCMU reduced RLER considerably in both control and salt-treated plants and reduced the advantage of control plants during the day. Conditions of low light also reduced the differences in RLER between control and salt-treated plants. When salt was removed from the root medium of non-DCMU plants, the expansion rates equalled that of the controls within 24 h and remained at the same levels for the following 3 d measurement period: this recovery applied to leaves of all ages. Salt-grown plants with no photosynthesis (DCMU treatments) also increased their expansion rates upon removal of salt from the root medium, thus providing further evidence that growth was not limited by carbohydrate status, i.e. that salt influences growth primarily via its effects on the rate of utilization of stored assimilates.     

Effects of external NaCl on the growth of Atriplex amnicola and the ion relations and carbohydrate status of the leaves

Abstract Atriplex amnicola, was grown in nutrient solution cultures with concentrations of NaCl up to 750 mol m^?3. The growth optimum was at 25–50 mol m^?3 NaCl and growth was 10–15% of that value at 750 mol m^?3 NaCl. Sodium chloride at 200 mol m^?3 and higher reduced the rate of leaf extension and increased the time taken for a leaf to reach its maximal length. Concentrations of Na⁺, K⁺ and Mg²⁺ in leaves of different ages were investigated for plants grown at 25, 200 and 400 mol m^?3 NaCl. Although leaves of plants grown at 200 and 400 mol m^?3 NaCl had high Na⁺ concentrations at young developmental stages, much of this Na⁺ was located in the salt bladders. Leaves excluding bladders had low Na⁺ concentrations when young, but very high in Na⁺ when old. In contrast to Na⁺, K⁺ concentrations were similar in bladders and leaves excluding bladders. Concentrations of K⁺ were higher in the rapidly expanding than in the old leaves. At 400 mol m^?3 NaCl, the K⁺:Na⁺ ratios of the leaves excluding bladders were 0.4–0.6 and 0.1 for rapidly expanding and oldest leaves, respectively. The Na⁺ content in moles per leaf, excluding bladders, increased linearly with the age of the leaves; concurrent increases in succulence were closely correlated with the Na ⁺ concentration in the leaves excluding the bladders. Soluble sugars and starch in leaves, stems and buds were determined at dusk and dawn. There was a pronounced diurnal fluctation in concentrations of carbohydrates. During the night, most plant parts showed large decreases in starch and sugar. Concentrations of carbohydrates in most plant organs were similar for plants grown at 25 and 400 mol m^?3 NaCl. One notable exception was buds at dusk, where sugar and starch concentrations were 30–35% less in plants grown at 400 mol m^?3 NaCl than in plants grown at 25 mol m^?3 NaCl. The data indicate that the growth of A. amnicola at 400 mol m^?3 NaCl is not limited by the availability of photosynthate in the plant as a whole. However, there could have been a growth limitation due to inadequate organic solutes for osmotic regulation.     

The characterization of inhibition of net nitrate uptake by salt in salt-tolerant barley (Hordeum vulgare L. cv. California Mariout)

Barley seedlings (Hordeum vulgare L. cv. California Mariout) grown hydroponically for 14-19 d without addition of NaCl were used for describing the effects of salt application on net nitrate uptake and for the calculation of kinetic parameters. The addition of NaCl, KCl, CaCl2, and Na2SO4 to the uptake solution in the experiments led to similar inhibition of nitrate uptake, only at low and very high salt concentrations were ion-specific effects found. The same decrease in nitrate uptake can also be achieved by sorbitol or betaine at corresponding osmolalities. Thus it was concluded that the inhibition of uptake was caused mainly by the osmotic effects of salts. Differences in the mechanisms of inhibition were detected between the two systems of nitrate uptake (high affinity system: HATS, and low affinity system: LATS). The HATS was inhibited non-competitively by NaCl, an apparent Ki of 60 mol m^-3 was calculated using a Dixon-plot. Fitting an equation assuming a non-competitively inhibited HATS by computer program to the raw data resulted in an apparent Ki of about 37 mol m^-3. In contrast, the LATS was affected in a complex way: up to 60 mol m^-3 NaCl the affinity was increased, which led to a stimulation of nitrate uptake at low nitrate concentrations (<2 mol m^-3). An inhibition of the LATS became obvious at concentrations above 3 mol m^-3 nitrate (for all applied salt concentrations) or with 100 mol m^-3 NaCl (throughout the whole nitrate range). Related plots of the data pointed to a competitive effect.Key words: Hordeum vulgare L., net nitrate uptake, high affinity transport system (HATS), low affinity transport system (LATS), salt, inhibition, apparent kinetic parameters.      

Replacement of nitrate by ammonium as the nitrogen source increases the salt sensitivity of pea plants. II. Inter- and intracellular solute compartmentation in leaflets

Pea plants (Pisum sativum L. cv. ‘Kleine Rheinländerin’) grown on ammonium or nitrate as the sole nitrogen source were treated with 50 mol m⁻³ NaCl. Four days after salt addition, ammonium-grown plants developed the first visible damage symptoms (wilting of leaflets, starting from the margins). Salt-treated, nitrate-grown plants were not affected during the experimental period. In order to obtain a better understanding of this differential salt sensitivity, we investigated the inter- and intracellular ion compartmentation of leaflets under both nutritional conditions by analysing ion concentrations in the apoplastic space, in chloroplasts and in protoplasts. When the leaves of nitrate- and ammonium-grown plants had attained similar sodium and chloride contents (after different times of exposure to salinity), the latter had a considerably lower chloroplastic chloride (and also sulphate) concentration. The results suggest that the intracellular compartmentation capacity of ammonium-grown plants is considerably lower than that of nitrate-grown plants. Ion toxicity appeared to initiate breakdown of metabolism in parts of the mesophyll tissue of ammonium-grown plants, causing an abrupt release of solutes into the apoplast, which coincided with the appearance of visible damage. Although the ammonium concentrations in leaves increased dramatically in the later phases of damage development, they were too low to cause the collapse of electrochemical gradients at the time at which damage became visible. Thus, the reason for a lower compartmentation capacity under ammonium nutrition remains as yet unclear.     

Growth cycle stage-dependent NaCl induction of plasma membrane H+-ATPase mRNA accumulation in de-adapted tobacco cells

A cDNA clone encoding an isoform of the plasma membrane H⁺-ATPase was isolated from Nicotiana tabacum. The steady-state plasma membrane H⁺-ATPase message levels were the same in unadapted tobacco cells and tobacco cells adapted to 428 mol m⁻³ NaCl. When cells adapted to 428 mol m⁻³ NaCl maintained in the absence of NaCl (deadapted) for an excess of 100 passages were exposed to 400 mol m⁻³ NaCl for 24 h, there was an increased accumulation of plasma membrane H⁺-ATPase message. The NaCl responsiveness of the deadapted cells was dependent upon the growth cycle stage. Alterations in the levels of plasma membrane FT-ATPase message during the growth cycle support a role for the H⁺-ATPase in cell growth. These results document the induction by NaCl of plasma membrane FT-ATPase message accumulation in tobacco cells, and suggest that enhanced expression of the plasma membrane FT-ATPase has a role in the short term response of cells of NaCl, but is not necessarily involved in long-term adaptation.     

Effects of silicon on enzyme activity and sodium,potassium and calcium concentration in barley under salt stress

Two contrasting barley (Hordeum vulgare L.) cultivars: Kepin No.7 (salt sensitive), and Jian 4 (salt tolerant) were grown in a hydroponics system containing 120 mol m^-3 NaCl only and 120 mol m^-3 NaCl with 1.0 mol m^-3 Si (as potassium silicate). Compared with the plants treated with salt alone, superoxide dismutase (SOD) activity in plant leaves and H⁺-ATPase activity in plant roots increased, and malondialdehyde (MDA) concentration in plant leaves decreased significantly for both cultivars when treated with salt and Si. The addition of Si was also found to reduce sodium but increase potassium concentrations in shoots and roots of salt-stressed barley. Sodium uptake and transport into shoots from roots was greatly inhibited by added Si under salt stress conditions. However, Si addition exhibited little effect on calcium concentrations in shoots of salt-stressed barley. Thus, Si-enhanced salt tolerance is attributed to selective uptake and transport of potassium and sodium by plants. The results of the present study suggest that Si is involved in the metabolic or physiological changes in plants. This revised version was published online in June 2006 with corrections to the Cover Date.     

Salt tolerance in Eucalyptus spp.: identity and response of putative osmolytes

In four species of salt-tolerant eucalypts (Eucalyptus raveretiana, E. spathulata, E. sargentii and E. loxophleba), we found substantial concentrations of quercitol – a cyclitol known for its accumulation in seeds of Quercus. Quercitol was absent in old foliage of E. globulus, a species noted for greater susceptibility to salinity, and also absent in the moderately tolerant E. camaldulensis, but, relative to other species, both had higher foliar concentrations of inositol. Simple sugars and cyclitols accumulated to osmotically significant concentrations in all species. The osmotic potential of expressed sap was always less than that of the external ‘soil’ solution and increasing salinity produced predictable reductions in growth and increases in ion concentrations in foliage of saplings of four eucalypt species. The more salt-tolerant species, E. spathulata, E. loxophleba and E. sargentii, were able to maintain well-regulated leaf Na⁺ concentrations even at 300 mol m⁻³ NaCl. These more salt-tolerant species also showed an apparent increase in net selectivity for K⁺ over Na⁺ as salinity increased, irrespective of the Na⁺ : Ca²⁺ ratio of the external medium (range 25 : 1 to 75 : 1; Ca²⁺ always ≥ 4.0 mol m⁻³). By contrast, E. globulus was unable to exclude Na⁺ when exposed to higher NaCl concentrations (e.g. 200 and 300 mol m⁻³). Carbon isotope signatures of foliage reflected imposed salinity but were not strongly enough correlated with growth to support previous suggestions that isotope discrimination be a means of evaluating salt tolerance. On the other hand, patterns of sugar and cyclitol accumulation should be further explored in eucalypts as traits contributing to salt tolerance, and with potential use as markers in breeding programmes.     

How much sodium accumulation is necessary for salt tolerance in subspecies of the halophyte Atriplex canescens?

Two sympatric subspecies of the xerohalophyte Atriplex canescens Pursh. (Nutt.) were compared for 84 d in outdoor salinity trials in their native coastal desert environment in Sonora, Mexico. Subspecies linearis grows naturally on sea water in the high intertidal zone of estuaries while subspecies canescens grows on dunes. In lysimeter pot experiments, ssp. linearis exhibited 50% growth reduction when the mean root zone salinity reached 1160 mol m⁻³ NaCl compared to just 760 mol m⁻³ for ssp. canescens. When irrigated with sea water in a flood plot, ssp. linearis had 50% higher growth rates than ssp. canescens. The specialization of ssp. linearis for a saline environment was associated with greater net transport of Na⁺ from root to shoot, greater Na⁺ accumulation in the leaves and a higher Na:K ratio in the leaves compared to ssp. canescens. On the other hand, the two subspecies achieved approximately the same degree of osmotic adjustment in the leaves, equal to two to three times the external salinity, and had similar water use efficiencies. Even at relatively low salinities, both subspecies accumulated larger quantities of Na⁺ for osmotic adjustment than K⁺. The results suggest that breeding for Na⁺ accumulation rather than exclusion might be the more effective strategy for improving salt tolerance of conventional crop plants.     

Damaging mechanisms of chilling- and salt stress to <Emphasis Type="Italic">Arachis hypogaea</Emphasis> L. leaves

To investigate damaging mechanisms of chilling and salt stress to peanut (Arachis hypogaea L.) leaves, LuHua 14 was used in the present work upon exposure to chilling temperature (4°C) accompanied by high irradiance (1,200 μmol m⁻² s⁻¹) (CH), salt stress accompanied by high irradiance (1,200 μmol m⁻² s⁻¹) (SH), and high-irradiance stress (1,200 μmol m⁻² s⁻¹) at room temperature (25°C) (NH), respectively. Additionally, plants under low irradiance (100 μmol m⁻² s⁻¹) at room temperature (25°C) were used as control plants (CK). Relative to CK and NH treatments, both the maximal photochemical efficiency of PSII (F_v/F_m) and the absorbance at 820 nm decreased greatly in peanut leaves under CH and SH stress, which indicated that severe photoinhibition occurred in peanut leaves under such conditions. Initial fluorescence (F_o), 1 − q_P and nonphotochemical quenching (NPQ) in peanut leaves significantly increased under CH- and SH stress. Additionally, the activity of superoxide dismutase (SOD), one of the key enzymes of water-water cycle, decreased greatly, the accumulation of malondialdehyde (MDA) and membrane permeability increased. These results suggested that damages to peanut photosystems might be related to the accumulation of reactive oxygen species (ROS) induced by excess energy, and the water-water cycle could not dissipate energy efficiently under the stress of CH and SH, which caused the accumulation of ROS greatly. CH and SH had similar damaging effects on peanut photosystems, except that CH has more severe effects. All the results showed that CH- and SH stress has similar damaging site and mechanisms in peanut leaves.     

Salt stress and fluctuating light have separate effects on photosynthetic acclimation,but interactively affect biomass

In nature, soil salinity and fluctuating light (FL) often occur concomitantly. However, it is unknown whether salt stress interacts with FL on leaf photosynthesis, architecture, biochemistry, pigmentation, mineral concentrations, as well as whole-plant biomass. To elucidate this, tomato (Solanum lycopersicum) seedlings were grown under constant light (C, 200 μmol m⁻² s⁻¹) or FL (5–650 μmol m⁻² s⁻¹), in combination with no (0 mM NaCl) or moderate (80 mM NaCl) salinity, for 14 days, at identical photoperiods and daily light integrals. FL and salt stress had separate effects on leaf anatomy, biochemistry and photosynthetic capacity: FL reduced leaf thickness as well as nitrogen, chlorophyll and carotenoid contents per unit leaf area, but rarely affected steady-state and dynamic photosynthetic properties along with abundance of key proteins in the electron transport chain. Salt stress, meanwhile, mainly disorganized chloroplast grana stacking, reduced stomatal density, size and aperture as well as photosynthetic capacity. Plant biomass was affected interactively by light regime and salt stress: FL reduced biomass in salt stressed plants by 17%, but it did not affect biomass of non-stressed plants. Our results stress the importance of considering FL when inferring effects of salt-stress on photosynthesis and productivity under fluctuating light intensities.     

Effects of salt on growth,ion accumulation,photosynthesis and leaf anatomy of the mangrove,<Emphasis Type="Italic"> Bruguiera parviflora</Emphasis>

The effects of a range of salinity (0, 100, 200 and 400 mM NaCl) on growth, ion accumulation, photosynthesis and anatomical changes of leaves were studied in the mangrove, Bruguiera parviflora of the family Rhizophoraceae under hydroponically cultured conditions. The growth rates measured in terms of plant height, fresh and dry weight and leaf area were maximal in culture treated with 100 mM NaCl and decreased at higher concentrations. A significant increase of Na⁺ content of leaves from 46.01 mmol m^-2 in the absence of NaCl to 140.55 mmol m^-2 in plants treated with 400 mM NaCl was recorded. The corresponding Cl^- contents were 26.92 mmol m^-2 and 97.89 mmol m^-2. There was no significant alteration of the endogenous level of K⁺ and Fe²⁺ in leaves. A drop of Ca²⁺ and Mg²⁺ content of leaves upon salt accumulation suggests increasing membrane stability and decreased chlorophyll content respectively. Total chlorophyll content decreased from 83.44 g cm^-2 in untreated plants to 46.56 g cm^-2 in plants treated with 400 mM NaCl, suggesting that NaCl has a limiting effect on photochemistry that ultimately affects photosynthesis by inhibiting chlorophyll synthesis (ca. 50% loss in chlorophyll). Light-saturated rates of photosynthesis decreased by 22% in plants treated with 400 mM NaCl compared with untreated plants. Both mesophyll and stomatal conductance by CO₂ diffusion decreased linearly in leaves with increasing salt concentration. Stomatal and mesophyll conductance decreased by 49% and 52% respectively after 45 days in 400 mM NaCl compared with conductance in the absence of NaCl. Scanning electron microscope study revealed a decreased stomatal pore area (63%) in plants treated with 400 mM NaCl compared with untreated plants, which might be responsible for decreased stomatal conductance. Epidermal and mesophyll thickness and intercellular spaces decreased significantly in leaves after treatment with 400 mM NaCl compared with untreated leaves. These changes in mesophyll anatomy might have accounted for the decreased mesophyll conductance. We conclude that high salinity reduces photosynthesis in leaves of B. parviflora, primarily by reducing diffusion of CO₂ to the chloroplast, both by stomatal closure and by changes in mesophyll structure, which decreased the conductance to CO₂ within the leaf, as well as by affecting the photochemistry of the leaves.     

Salt activation and inhibition of membrane ATPase from roots of the halophyte Atriplex nummularia

Abstract Salt-stimulated ATPase activity in membrane preparations obtained from roots of Atriplex nummularia Lindl. at pH 5 was not suscep-tible to inhibition by KC1 or NaCl up to 450 mol m-3 but showed a broad peak of activity between 150 and 300 mol m^?3. At pH 8 stimulation occurred at 50 mol m^?3 but concentrations above 100 mol m^?3 depressed activity below the level of the MgATPase activity. By contrast, preparations from roots of Pisum sativum L. at pH 5 showed maximal stimulation at 25 to 50 mol m^?3 of NaCl or KC1; concentrations higher than 150 mol m^?3 depressed activity below that of MgATPase activity. At pH 8 maximal stimulation was observed at 5 to 10 mol m^?3 NaCl or KC1 while the threshold for inhibition was reduced to 15 mol m^?3. With increasing salt concentrations the pH profiles for NaCl stimulation of Atriplex ATPase activity (expressed as the difference between treatment and control) showed a progressive displacement of the apparent optimum towards lower pH. The shift was not apparent when stimulation was expressed as a percentage of MgATPase activity. This shift may be accounted for if NaCl stimulated the monovalent salt-activated ATPase activity but simultaneously inhibited MgATPase activity.     

Cellular and whole plant responses ofVigna radiata to NaCl stress

The effect of different NaCl regimes was examined on the growth and ion accumulation in whole plants and callus cultures ofVigna radiata. Whole plants grown in sand culture were watered with Hoagland's solution supplemented with 0–350 mol m⁻³ of NaCl. Callus cultures were initiated from leaves of 7-d old seedlings of the same seed stock and grown in modified PC-L2 medium containing the same levels of NaCl as in Hoagland's solution. Callus showed the same tolerance to salt as did the whole plant suggesting thatV. radiata appears to have a mechanism(s) for salt tolerance which operates at the cellular level. Ion analysis of whole plant showed that root sodium concentrations of the tolerant cultivar G-65 was much higher while shoot sodium was much less than those of salt sensitive cultivar ML-1. Callus cultures of cv. G-65 also accumulated higher Na⁺ levels. Thus, the greater salt tolerance of cv. G-65 was associated with the control of sodium accumulation at the shoot or cellular level. Communicated by J. POSPíŠILOVá     

Increasing NaCl and CaCl2 concentrations in the growth medium of quince leaves: II. Effects on shoot regeneration

Summary The effects of NaCl and CaCl₂ on shoot regeneration from quince (Cydonia oblonga BA L29 clone) leaves were investigated. Caulogenesis was induced on in vitro-grown leaves treated for 2d in liquid Murashige and Skoog (MS) medium with 11.3 μM 2,4-dichlorophenoxyacetic acid and cultured on MS gelled medium supplemented with 4.5 μM thidiazuron and 0.5 μM naphthaleneacetic acid. Three experiments were performed: in the first, we compared the effects of NaCl at 0, 25, 50, 100, and 200 mM in factorial combination with 3, 9, and 27 mM CaCl₂. In the second, NaCl was tested at 0, 5, 10, 20, 40, and 80 mM with CaCl₂ at 0.3, 1.0, and 3.0 mM. The third experiment was carried out with the same experimental design as the second one but replacing NaCl with Na₂SO₄. Shoot regeneration was evaluated after 50 d of culturing: 25 in darkness and 25 in white light. In the first experiment, shoot regeneration was very poor and was observed only at the lower salt concentrations. In the second experiment, the percentages of caulogenic leaves were much higher, but decreased with increasing NaCl concentration. The more pronounced negative effect of the highest NaCl concentrations appeared to be partly mitigated by CaCl₂ at 1 and 3 mM. The presence of 3 mM CaCl₂, in the experiment with Na₂SO₄, appeared to be even more effective in reducing the adverse effect of sodium stress on caulogenesis. This result was attributed to the lower Cl⁻ concentration in the growth medium, which resulted from replacing NaCl with Na₂SO₄. NaCl applied at low concentrations (5 and 10 mM) in combination with 3 mM CaCl₂ exerted a favorable effect on adventitious shoot regeneration. As regards the Na⁺ and Ca²⁺ interaction, when the Na⁺/Ca²⁺ ratio was below roughly 35 and 20, with NaCl and Na₂SO₄, respectively, at least 60% of leaves showed regenerating capacity, but optimal values of this ratio were not derived.     

Changes in ion and water content of individual shoot organs in a salt-tolerant and a salt-sensitive clone of Agrostis stolonifera L. during and subsequent to treatment with sodium chloride

Abstract Individual leaves and stems were analysed for Na⁺, Cl^?, K⁺ and water content in two clones of Agrostis stolonifera differing in salt resistance, during 14 d of treatment with NaCl, 100 and 200 mol m^?3, and a further 7 d in a salt-free medium. Great differences in ion and water content were revealed between individual organs, and organ-by-organ analysis also emphasized the differences between the clones better than whole shoot analysis. In both clones, Na⁺ and Cl^? accumulated to the greatest degree in the older leaves, but for corresponding organs, the concentrations were lower in the more tolerant clone. In the sensitive clone, the lowest leaves dehydrated in 200 mol m^?3 NaCl and failed to recover, while the plants of the more resistant clone maintained viable water content in all organs. In the resistant clone, K⁺ concentration decreased less in response to salt treatment than in the more sensitive clone. For a full appreciation of the plants' reactions, it was found necessary to express the analytical data on several bases, namely, per unit dry-weight, unit water, and total ion-content.