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     

Growth characteristic and ion contents of rice callus under the influence of NaCl and hydroxyproline

Calli of salt tolerant (Bhoora rata) and salt susceptible (GR₁₁) rice varieties were cultured on Linsmaeir and Skoog’s medium containing LD₅₀ concentration of NaCl (200 mM) and hydroxyproline (10 mM). Growth rate of callus and Na⁺, K⁺, Cl⁻, Mg⁺², and Ca⁺² contents of the cultured rice tissues were determined at the end of 0, 2, 4 and 6 weeks of incubation. Hydroxyproline resistant calli of both rice varieties when cultured on Linsmaeir and Skoog’s medium containing both NaCl and hydroxyproline showed increased dry weight and enhanced intracellular levels of K⁺, Mg⁺² and Ca⁺². The accumulation of Na⁺ and Cl⁻ ions was less in the hydroxyproline resistant calli.     

Growth, proline accumulation and ion content in sodium chloride-stressed callus of date palm

Summary Growth and physiological responses of date palm. Phoenix dactylifera L. cv. Barhee, callus to salinity stress were examined. Callus induced from shoot tips of offshoots was cultured on Murashige and Skoog medium supplemented with NaCl at concentrations ranging from 0 to 225 mM, in consective increments of 25 mM. Data obtained after 6 wk of exposure to salt have shown a significant increase in callus proliferation in response to 25 mM NaCl the lowest level tested, beyond which callus weight decreased. At 125 mM NaCl and higher, callus growth was nearly completely inhibited. Physiological studies on callus exposed to salt stress have shown an increase in proline accumulation in response to increased salinity. Proline accumulation was correlated to callus growth inhibition. Furthermore, increasing the concentration of NaCl in the culture medium generally resulted in a steady increase in Na⁺ and reduction in K⁺ concentrations. However, at 25 mM NaCl, the only level at which callus growth was significantly enhanced, an increase in K⁺ content was noted, in comparison to the NaCl free control. In response to increasing external NaCl level, the Na⁺/K⁺ ratio increased The Na⁺/K⁺ ratio was positively correlated to proline accumulation and hence callus growth inhibition. This study provides, an understanding of the response of date palm callus to salinity, which is important for future studies aimed at developing strategies for selecting and characterizing somaclonal variants tolerant to salt stress.     

<Emphasis Type="SmallCaps">l</Emphasis>-tryptophan decarboxylase activity and tryptamine accumulation in callus cultures of <Emphasis Type="Italic">Vinca minor</Emphasis> L.

l-tryptophan decarboxylase (TDC, EC 4.1.1.28) catalyses the formation of tryptamine from tryptophan, and therefore it plays a role in terpenoid indole alkaloids biosynthesis. In this study, TDC activity and tryptamine accumulation were monitored in callus cultures of important medicinal plant Vinca minor L. Callus cultures, established from leaf tissues, were incubated on Murashige and Skoog (MS) medium supplemented with 4.4 μM kinetin and different concentrations (0.44, 1.1, 2.2, 4.4 and 6.6 μM) of naphthaleneacetic acid (NAA), and grown either in the dark or under 16 h photoperiod. When the basal enzyme activity of TDC was determined in these cultures, it was 0.5–0.7 nmol tryptamine mg⁻¹ prot. min⁻¹. Moreover, this activity remained linear over time and over protein concentrations, and with optimum pH levels between 6.5 and 7.5, and an optimum temperature of 35°C. The Michaelis–Menten constant (K_m) for l-tryptophan was 1.3 mM. TDC cofactor, pyridoxal-5′-phosphate (1 mM), increased the enzyme activity. During later stages of callus culture growth cycle, an increase in TDC activity was observed, and this activity depended on culture conditions and age of callus cultures. In addition, TDC activity and tryptamine accumulation in callus cultures were strongly enhanced by light treatment.     

Selection of callus cultures of sugarcane (Saccharum sp.) tolerant to NaCl and their response to salt stress

Stable callus cultures tolerant to NaCl (68 mM) were developed from salt-sensitive sugarcane cultivar CP65-357 by in vitro selection process. The accumulation of both inorganic (Na⁺, Cl⁻ and K⁺) and organic (proline and soluble sugars) solutes was determined in selected and non-selected calli after a NaCl shock in order to evaluate their implication in in vitro salt tolerance of the selected lines. Both salt-tolerant and non-selected calli showed similar relative fresh weight growth in the absence of NaCl. No growth reduction was observed in salt-tolerant calli while a significant reduction about 32% was observed in nonselected ones when both were cultivated on 68 mM NaCl. Accumulation of Na⁺ was similar in both salt-tolerant and non-selected calli in the presence of NaCl. Accumulation of Cl⁻ was lower in NaCl-tolerant than in non-selected calli while proline and soluble sugars were more accumulated in salt-tolerant than in non-selected calli when both were exposed to salt. K⁺ level decreased more severely in non-selected calli than in NaCl-tolerant ones after NaCl shock. The results indicated that K⁺ and Cl⁻ may play a key role in in vitro salt-tolerance in sugarcance cell lines obtained by in vitro selection and that organic solutes could contribute mainly to counteract the negative water potential of the outside medium.     

Salinity tolerance of hydroponically grown <Emphasis Type="Italic">Pinus pinea</Emphasis> L. seedlings

The salinity tolerance and ion transport of 2-month-old seedlings of stone pine (Pinus pinea L.) grown in hydroponic solution containing various concentrations of NaCl (0–100 mM) were studied. The presence of salt of up to 100 mM did not significantly reduce growth. Seedling hydration was insensitive to salinity. High salt concentrations reduced K⁺ and Ca²⁺ uptake, root accumulation, and export to shoots. Na⁺ and Cl⁻ ions, representing the major part of the ionic uptake, were effectively compartmentalized in vacuoles. We concluded that seedlings of stone pine cultivated hydroponically were highly tolerant to salt concentrations of up to 100 mM for a culture period of 38 days. This tolerance was associated with the accumulation of Na⁺ and Cl⁻ ions in the shoots.     

Uptake of inorganic ions and compatible solutes in cultured mangrove cells during salt stress

Summary Callus of the mangrove plant, Sonneratia alba J. Smith, established from pistils of flower buds were cultured on solid Murashige and Skoog medium supplemented with 0 to 500 mM NaCl. Maximum growth was observed with 50 mM NaCl, and net growth of callus occurred for concentrations up to 200 mM NaCl. At 500 mM NaCl, growth of callus was completely inhibited, although a part of the tissue was still alive after 30 d. Cellular levels of Na⁺ and Cl⁻ were greatly increased by the treatment with NaCl. Uptake of K⁺ was also enhanced and was accompanied by increasing levels of Na⁺ and Cl⁻ so that the Na⁺/K⁺ ratio was almost constant (4.1–4.2) in callus grown with 50–200 mM NaCl. Levels of Mg²⁺ and Ca²⁺ were not changed significantly with 50–200 mM NaCl, whereas levels of free NH ₄ ⁺ , NO ₃ ⁻ and SO ₄ ²⁻ ions, which are convertible to organic compounds, were lowest in callus grown with 50 mM NaCl. The rate of conversion of ¹⁵NH ₄ ⁺ into macromolecules during 30 d culture with 0–100 mM NaCl did not vary greatly, but 200 mM NaCl reduced the biosynthesis of macromolecules from this ion. The highest rate of conversion of ¹⁵NO ₃ ⁻ into macromolecules was observed at 50 mM NaCl. Identification of compatible solutes with NMR-spectroscopy indicated that mannitol is the compatible solute for intact plants of Sonneratia alba, but no accumulation of mannitol was found in calluses, not even in those grown at high concentrations of NaCl.     

Salinity adaptation of plasma membrane H+-ATPase in the salt marsh plant Spartina patens: ATP hydrolysis and enzyme kinetics

Spartina patens, an intertidal C4 grass, grows in the upper salt marsh and tolerates coastal seawater salinity. The regulation of ion movement across the plasma membrane (PM) for plant salt tolerance is thought to be achieved by an electrochemical gradient generated by plasma membrane H⁺-ATPase. In this study, the change of PM H⁺-ATPase in response to NaCl was characterized for S. patens callus. Callus was cultured for 10 weeks under salinity levels of 0 mM, 170 mM, 340 mM, and 510 mM NaCl. Plasma membrane was isolated from a Dextran/PEG aqueous polymer two-phase system and the purity was demonstrated with membrane enzyme markers. There was a significant increase (up to 2-3 fold) of PM H⁺-ATPase activity when callus was grown on media containing NaCl. The incremental activation of PM H⁺-ATPase activity would enable the cell to tolerate higher cytoplasmic NaCl concentrations. PM H⁺-ATPase appeared to have a higher Vmax and a lower substrate concentration (Km to reach Vmax. When growth medium salinity increased from 0 mM to 170 and 340 mM, the Vmax of H⁺-ATPase increased from 0.64 to 1.00 and 1.73, respectively, while the Km decreased from 3.58 to 2.07 and 2.44 mM, respectively. In vitro NaCl inhibition kinetic data revealed a pattern of non-competitive inhibition by NaCl on PM H⁺-ATPase. The response of PM H⁺-ATPase in S. patens callus suggests that this species has evolved mechanisms that can regulate this important enzyme when cells are exposed to NaCl.     

Exogenous Putrescine Reduces Sodium and Chloride Accumulation in NaCl-Treated Calli of the Salt-Sensitive Rice Cultivar I Kong Pao

In order to gain information on the putative involvement of polyamines (PAs) in the response of rice cells to salinity, mature embryo-derived calli issued from the salt-sensitive cultivar I Kong Pao were exposed for 3 months to the simultaneous presence of NaCl (0, 150 and 300 mM) and exogenous polyamines (putrescine (Put): 1 and 10 mM; spermidine (Spd): 1 and 10 mM; spermine (Spm): 1 mM). Callus growth, endogenous PAs, Na⁺, K⁺ and Cl⁻ concentrations were quantified and analysed in relation to cell viability based on 2,3,5-triphenytetrazolium chloride (TTC) reduction. All exogenous PAs were efficiently absorbed from the external medium. Exogenous Put 1 mM clearly stimulated growth of salt-stressed calli in relation to a decrease in both Na⁺ and Cl⁻ accumulation. In contrast, Spd 10 mM and Spm 1 mM exacerbated the deleterious impact of NaCl on callus growth and induced a decrease in K⁺ concentration. While Put helped in the maintenance of cell viability, Spd 10 mM and Spm 1 mM decreased cell viability, mainly in relation to an inhibition of the alternative respiratory pathway. It is proposed that Put may assume positive functions in salt stress resistance in rice.     

Ethylene and nitric oxide are involved in maintaining ion homeostasis in <Emphasis Type="Italic">Arabidopsis</Emphasis> callus under salt stress

In the present study, the role of ethylene in nitric oxide (NO)-mediated protection by modulating ion homeostasis in Arabidopsis callus under salt stress was investigated. Results showed that the ethylene-insensitive mutant etr1-3 was more sensitive to salt stress than the wild type (WT). Under 100 mM NaCl, etr1-3 callus displayed a greater electrolyte leakage and Na⁺/K⁺ ratio but a lower plasma membrane (PM) H⁺-ATPase activity compared to WT callus. Application of exogenous 1-aminocyclopropane-1-carboxylic acid (ACC, an ethylene precursor) or sodium nitroprusside (SNP, a NO donor) alleviated NaCl-induced injury by maintaining a lower Na⁺/K⁺ ratio and an increased PM H⁺-ATPase activity in WT callus but not in etr1-3 callus. The SNP actions in NaCl stress were attenuated by a specific NO scavenger or an ethylene biosynthesis inhibitor in WT callus. Under 100 mM NaCl, the NO accumulation and ethylene emission appeared at early time, and NO production greatly stimulated ethylene emission in WT callus. In addition, ethylene induced the expression of PM H⁺-ATPase genes under salt stress. The recovery experiment showed that NaCl-induced injury was reversible, as signaled by the similar recovery of Na⁺/K⁺ ratio and PM H⁺-ATPase activity in WT callus. Taken together, the results indicate that ethylene and NO cooperate in stimulating PM H⁺-ATPase activity to modulate ion homeostasis for salt tolerance, and ethylene may be a part of the downstream signal molecular in NO action.     

Selection and characterization of mannitol-tolerant callus lines of Vigna radiata (L.) Wilczek

An osmotically (mannitol) tolerant callus line of Vigna radiata (L.) Wilczek has been isolated from callus cultures grown on modified PC-L2 medium supplemented with increasing concentrations of mannitol. The tolerance was stable and retained after growth in the absence of mannitol selection for 2 months. The growth of the tolerant line, in the presence of mannitol (540 mol m^-3) was comparable to that of a sensitive callus line growing in the absence of mannitol. This line not only grew well on media containing up to 720 mol m^-3 mannitol, but also required 450 mol m^-3 mannitol for its optimal growth. Osmotically tolerant callus also showed increased tolerance to NaCl (0–250 mol m^-3) stress as compared to sensitive callus. Accumulation of Na⁺ was lower, and the level of K⁺ was more stable in osmotically tolerant than in sensitive calli, when both were exposed to salt. The free proline content of both tolerant and sensitive calli increased on media supplemented with mannitol or NaCl. However, the proline content of sensitive callus was higher than in tolerant callus in the presence of same concentrations of mannitol or NaCl.Abbreviations NAA -naphthaleneacetic acid - 2,4-d 2,4-dichlorophenoxyacetic acid - BAP 6-benzylaminopurine     

Sodium transport in basil

In order to diversify the production of plants with pharmacological interest, it is important to understand the mechanisms involved in their tolerance to environmental constraints, such as salinity. Basil (Ocimum basilicum), known for its therapeutic uses, has been claimed to be salt tolerant, but physiological aspects of this behavior remain unknown. Since salt tolerance is known to be associated with several characteristics concerning Na⁺ transport to leaves, we studied this function in hydroponically grown basil. We analyzed the response of 30-day-old seedlings to 25–50 mM NaCl applied for 15 days. Growth was poorly affected, indicating that these concentrations corresponded to the tolerated salinity range. Leaves accumulated Na⁺ at relatively high concentration, without dehydrating. Potassium concentration in leaf tissues was maintained close to control level, indicating that K⁺ was 15- to 25-fold preferred over Na⁺ for ion transport and deposition. Collection of xylem sap on detopped plants revealed that this preference was only 10-fold for ion introduction into root xylem sap. Short-term (24 h) changes in Na⁺ distribution between organs after stem (steam) girdling suggested that Na⁺ downward recirculation by phloem occurred. Although modest, this transport might have augmented K⁺ selectivity of ion deposition in leaves.     

Proline accumulation and sodium sulfate tolerance in callus cultures of Brassica napus L. cv. Westar

Callus cultures of Brassica napus L. cv. Westar were selected which contained 5 – 6 times more proline than unselected callus. Callus pieces from these cultures were able to survive much better after subculture to medium containing 105 mM Na₂SO₄ than unselected callus, or unselected callus cultured on exogenous proline before or during transfer to the salt. Exogenous proline was rapidly absorbed. In unselected callus there was a peak in proline accumulation ca. 2 days after transfer to Na₂SO₄, followed by a decline. In contrast proline accumulation in tolerant callus was linear with time, reaching maximum levels at 8 days. Proline levels induced by exposure to salt were maintained in the absence of stress.Abbreviations DW Dry weight - FW Fresh weight     

In vitro selection and characterization of Ni-tolerant callus lines of Setaria italica L

Nickel tolerant callus lines of Setaria italica L. were developed from callus cultures grown on MS medium supplemented with 0.5 mg·dm⁻³ kinetin+2.0 mg·dm⁻³ 2,4-D+2.0 mg·dm⁻³ Ni⁺². Standard growth parameters such as callus fresh and dry weight, growth tolerance index were used as indicators of nickel toxicity. Measurements as early as 2 weeks after the beginning of the treatments did not yield consistent results. However, growth tolerance index at 4, and 8 weeks after the beginning of treatments yielded significant differences among the non-tolerant and tolerant calli. The tolerant calli has enhanced growth at 2.0 mg·dm⁻³ Ni⁺² while non-tolerant calli showed a reverse trend in growth in the presence of 2.0–2.5 mg·dm⁻³ of nickel. The tolerant calli differentiated into mass of embryogenic calli within 4 weeks of culture which could be maintained for prolonged period without loss of regenerative capacity.     

The effect of NaCl on proline accumulation in potato seedlings and calli

The effects of salt stress were studied on the accumulation and metabolism of proline and its correlation with Na⁺ and K⁺ content in shoots and callus tissue of four potato cultivars, viz., Agria, Kennebec (relatively salt tolerant), Diamant and Ajax (relatively salt sensitive). Na⁺ and proline contents increased in all cultivars under salt stress. However, K⁺ and protein contents decreased in response to NaCl treatments. The activities of enzymes involved in proline metabolism, Δ¹-pyrroline-5-carboxylate synthetase (P5CS) and proline dehydrogenase (ProDH) increased and decreased, respectively, in response to elevated NaCl concentrations. The changes of P5CS and ProDH activities in more salt sensitive cultivars (Diamant, Ajax) were more than those in the tolerant ones. Then the stimulation of synthesis in combination with a partially increase of protein proteolysis, a decrease in proline utilization and inhibition of oxidation resulted in high proline contents in seedlings and calli under salt stress. In callus tissue, reduced growth and cell size may be partially responsible for high proline accumulation in response to high NaCl levels. However, although the basic proline contents in the seedlings of more salt tolerant cultivars were higher than the sensitive ones, a clear relationship was not generally observed between accumulation of proline and salt tolerance in potato.     

Comparison of the effects of NaCl and KCl at the roots on seedling growth,cell death and the size,frequency and secretion rate of salt glands in leaves of <Emphasis Type="Italic">Limonium sinense</Emphasis>

Twenty days’ exposure to 50 or 100 mM NaCl in the rooting medium substantially increased fresh and dry weights of seedling shoots of the recretohalophyte Limonium sinense while 200 or 300 mM were increasingly inhibitory. KCl treatment was only slightly stimulating (50 mM) or strongly inhibitory (100–300 mM). Lesser effects on leaf area were also seen. Diameter of foliar salt glands was significantly larger than that of controls in 100 and 200 mM NaCl with the effect being reversed at higher concentrations. Gland enlargement was also observed in the presence of 100 mM KCl, while larger concentrations reduced gland size. Generally, gland diameter was larger in the presence of NaCl than in KCl. NaCl and KCl also increased gland number per leaf and secretion rate per gland. At 100 and 200 mM NaCl or KCl, Na⁺ secretion per leaf from NaCl-treated plants exceeded K⁺ secretion rate from KCl-treated plants while at 200 mM, Na⁺ secretion per gland was significantly higher for Na⁺ than for K⁺. Evidence of cell death in leaves of salt-treated plants using Evans blue staining indicates that release of cell contents through loss of membrane integrity contributed to the secretion values. We conclude that the greater tolerance of L. sinenseto to NaCl compared to KCl is linked to the more effective secretion of Na⁺ than of K⁺ and, in turn, to a greater stimulation of salt gland formation and activity and larger gland diameter.     

Effects of Na2SO4, K2SO4 and KCl on Growth and Ion Uptake of Callus Cultures of Vaccinium corymbosum L. cv. Blue Crop

Non-selected and Na₂SO-, K₂SO₄- or KCl-selected callus culturesof Vaccinium corymbosum L. cv. Blue Crop were grown on mediasupplemented with 0, 25 and 50 mM Na₂SO₄ (non-selected and Na₂SO(-selectedonly), 0, 25 and 50mMK₂SO₄ (non-selected and K₂SO₄-selectedonly) or 0, 50 and 100 mM KCl (non-selected and KCl-selectedonly). On all media, growth of selected callus (on a fresh-weightor dry-weight basis) was greater than that of non-selected callus,and selected callus grew optimally on the level and type ofsalt on which it was selected. Selected callus was friable andmaintained a higher f. wt:d. wt ratio. Tissue water potentialin selected callus was more negative than in non-selected callus. Flame photometry and chloridometry showed Na⁺, K⁺ and Cl^–accumulated in callus to concentrations equal to or greaterthan the initial concentration in the medium. Turbidometry showedthat tissue SO₄^2- concentration was lower than the concentrationin the medium. In most cases selected callus accumulated moreNa⁺, K^sup, SO₄^2– or Cl^– than non-selected callus.Vacuolar ion concentration was measured by electronprobe X-raymicroanalysis, and on most media selected callus had highervacuolar ion concentrations than non-selected callus. SO₄^2–and Cl^– were accumulated in the vacuoles at concentrationshigher than the external medium, but vacuolar Na⁺ concentrationdid not reach external concentration on Na₂SO₄ and on potassiumsalts was maintained between 12 and 17 mM. Vacuolar K⁺ concentration(approx. 142–191 mM on no salt) decreased on Na₂SO₄ andincreased on K₂SO₄ and KCl. There was no precise correlation between total or specific ionaccumulation (Na⁺, K⁺, SO₄^2– and Cl^– and fresh-weightyield. Results suggest that selection results in adaptationin response to decreased water potential of the medium. Vaccinium corymbosum, blueberry, electronprobe X-ray microanalysis, callus, in vitro selection, salt tolerance, KCl, K₂SO₄, Na₂SO₄     

In vitro recurrent selection of potato: production and characterization of salt tolerant cell lines and plants

A stable salt-tolerant potato cell line, able to grow on media containing 60–450 mM NaCl (i.e. low to high salinity) was selected. Callus grown on 120 or 150 mM NaCl showed higher fresh weights than the rest of the treatments. Replacing NaCl by KCl or Na2SO4 showed that reductions in fresh weight were mainly due to the presence of Na+ ions. When PEG 6000 was added to the medium instead of salt, the salt tolerant cell lines were unable to overcome the PEG-induced water stress. Whole plants, regenerated from salt tolerant callus, exhibited salt stress tolerance as evidenced by their higher fresh and dry weights when watered with 90 mM NaCl, and they also produced more tubers per plant under salt stress. Salt-tolerant plants differed phenotypically from control plants both in terms of leaf shape, tuber flesh and skin colour, which was reddish. In addition, DNA fingerprinting by RAPDs, with 70 different primers, confirmed that the salt tolerant regenerants also differed genotypically from the control, salt sensitive Kennebec potato plants from which they had been selected. This revised version was published online in June 2006 with corrections to the Cover Date.     

<Emphasis Type="Italic">In vitro</Emphasis> selection of NaCl-tolerant callus lines and regeneration of plantlets in a bamboo (<Emphasis Type="Italic">Dendrocalamus strictus</Emphasis> Nees)

Summary Sodium chloride-tolerant plantlets of Dendrocalamus strictus were regenerated successfully from NaCl-tolerant embryogenic callus via somatic embryogenesis. The selection of embryogenic callus tolerant to 100 mM NaCl was made by exposing the callus to increasing (0–200 mM) concentrations of NaCl in Murashige and Skoog medium having 3% (w/v) sucrose, 0.8% (w/v) agar, 3.0 mg l⁻¹ (13.6 μM) 2,4-dichlorophenoxyacetic acid (2,4-D), and 0.5mg l⁻¹ (2.3μM) kinetin (callus initiation medium). The tolerance of the selected embryogenic callus to 100 mM NaCl was stable through three successive transfers on NaCl-free callus initiation medium. The tolerant embryogenic callus had high levels of Na⁺, sugar, free amino acids, and proline but a slight decline was recorded in K⁺ level. The stable 100 mM NaCl-tolerant embryogenic callus differentiated somatic embryos on maintenance medium [MS medium +3% sucrose +0.8% agar +2.0 mg l⁻¹ (9.0 μM) 2,4-D+0.5 mg l⁻¹ (2.3 μM) kinetin] supplemented with different (0–200 mM) concentrations of NaCl. About 39% of mature somatic embryos tolerant to 100 mM NaCl germinated and converted into plantlets in germination medium [half-strength MS+2% sucrose+0.02 mg l⁻¹ (0.1 μM) α-naphthaleneacetic acid +0.1 mg l⁻¹ (0.49 μM) indole-3-butyric acid] containing 100 mM NaCl. Of these plantlets about 31% established well on transplantation into a garden soil and sand (1:1) mixture containing 0.2% (w/w) NaCl.     

Development of callus and suspension cultures of potato resistant to NaCl and mannitol and their response to stress

Callus and suspension cultures adapted to various concentrations of NaCl or mannitol were developed from the cultivated potato Solanum tuberosum cv. Desire. Growth of the calli was less inhibited by mannitol than by iso-osmotic concentrations of NaCl. Reduction of growth by both NaCl and mannitol was considerably lower in osmotically adapted calli than in non-adapted ones. Salt-adapted suspension cultures that grew in the medium to which they had been originally adapted had a shorter lag in growth as well as a shorter time required to achieve the maximum growth, as compared with non-adapted cells. Suspension cultures adapted to NaCl concentrations higher than 150 mM were obtained only after preadaptation to osmotic stress. Adaptation of these cells was found to be stable. Accumulation of Na⁺ was lower and level of K⁺ was more stable in osmotically adapted than in non-adapted calli, when both were exposed to salt. Potassium level in NaCl-adapted calli exposed to saline medium was lower than that in non-adapted calli in standard medium. The maximum of Cl^– and Na⁺ accumulation was reached at higher external salt concentration in salt-adapted than in non-adapted suspension cultures. In both callus and suspension cultures, Cl^– accumulated more than Na⁺. Potassium level decreased more in non-adapted than in NaCl-adapted suspension cultures. The decrease of osmotic potential in osmotically adapted calli exposed to mannitol and in salt-adapted calli and suspension cultures exposed to salt was correlated to the increase of the external concentration. Such a correlation was not found in osmotically adapted calli exposed to salt. Non-electrolytes were found to be the main contributors to the decrease is osmotic potential in both callus and suspension cultures.