SOME DELETERIOUS EFFECTS OF LONG-TERM SALT STRESS ON GROWTH,NUTRITION, AND PHYSIOLOGY OF GERBERA (GERBERA JAMESONII L.) AND POTENTIAL INDICATORS OF ITS SALT TOLERANCE

Tolerance of gerbera (Gerbera jamesonii L.) to long-term sodium chloride (NaCl) salt stress was evaluated by subjecting plants to 0, 10, 20, 30 and 40 mM NaCl levels for ten weeks. Increased NaCl led to a significant decrease in leaf and stem biomass. Salt stress significantly affected sodium (Na⁺), potassium (K⁺) concentrations in leaves, stems and roots leading to sharp declines in K⁺/Na⁺ ratios. Magnesium concentrations in stems and roots also showed significant declines. Adverse effect of salt stress on chlorophyll content was also significant. Proline seemed less effective in osmotic adjustment under long-term high salt stress. Switching from vegetative to reproductive growth phase was crucial for certain physiological functions. Leaf Na⁺ concentration showed significant correlation with important traits. These data suggest that NaCl threshold level in irrigation water for gerbera is around 10 mM. Leaf fresh weight, chlorophyll content and leaf K⁺/Na⁺ ratio are promising indicators of salt-sensitivity of gerbera.     

Response of Digitalis purpurea plants to temporary salinity

Abstract

The effect of two different levels of salinity upon adult plants of Digitalis purpurea has been studied. Seeds of D. purpurea plants were sown in pots of equal size and moistened with deionized water during one year. Afterwards, different treatments with NaCl were initiated, the concentrations being 100 mM and 200 mM NaCl in irrigation water during 63 days. Growth, measured as dry and fresh weight, and soluble protein contents, were lower in stressed plants than in control plants. Monovalent cation analysis showed that in leaves K⁺ plus Na⁺ (Total M) values did not change with the different treatments, but that in roots these values increased with the increasing salinity stress. On the other hand, proline levels were higher in stressed plants although the accumulation of this amino acid was not significant In leaves, Cl^? levels increased linearly with salinity degree, and the accumulation of this ion was faster than that of Na⁺, whereas in roots, the Cl^? level remained relatively low.

Total cardenolide levels in leaves and roots of the 100 mM NaCl plants were higher than those in 200 mM NaCl and control plants. We infer that moderate salinity conditions lead to raised cardenolide levels, principally in leaves, but the reason for this is not clear.     

Effects of Soil Alkalization on Osmotic Adjustment and Ion Balance in Sorghum (Sorghum Bicolor L.)

Sorghum (Sorghum bicolor L.) was grown on an alkalinized plot for 90 days. Inorganic ions and compatible solutes were measured to investigate the physiological adaptations by which sorghum tolerates natural alkaline stress. Plant growth was clearly inhibited. The stress led to increased Na⁺ content in roots but had only a small effect on Na⁺ accumulation in leaves; K⁺ content in roots was lower than that in leaves and stems; and Na⁺ content and Na⁺/K⁺ ratio were much higher in roots than in leaves and stems. These suggest that maintaining a substantially higher osmotic potential in roots for greater uptake of water and restricting the spread of Na⁺ to shoots are physiological adaptations to alkalinity. Soluble sugar was the main osmolyte in roots, stems, and leaves; proline, amino acids, and oxalates contributed to osmotic regulation slightly, and it was noteworthy that K⁺ played a major role in osmotic regulation in leaves.     

Lavandula multifida response to salinity: Growth,nutrient uptake,and physiological changes

Fern leaf lavender (Lavandula multifida L.) is a perennial shrub native to Almería with known medicinal properties, which grows in saline soils that are increasingly present in the Mediterranean region. However, the effects of salinity on the mineral nutrition and physiology of L. multifida are unknown. In the present study, we evaluated the salt resistance of this species and compared it with other members of the Lamiaceae . Plants of L. multifida were grown in pots in a mixture of sphagnum peat‐moss and Perlite, and treated with five different NaCl concentrations [10 (control), 30, 60, 100, and 200 mM NaCl] over a period of 60 d. The effects of different levels of salinity on mineral nutrient and osmolyte concentrations and on biomass were evaluated. Our results show that L. multifida plants were able to grow with 60 mM NaCl without significant biomass reduction. Na⁺ and Cl⁻ were the main contributors to the osmotic potential in both roots and leaves, whereas total soluble sugars (TSS) and proline made only a small contribution. The concentrations of TSS and proline showed different trends in the different organs: in roots, both showed the highest concentrations at 60 mM NaCl, whereas in leaves TSS increased and proline decreased with increasing salt stress. To survive salinity, L. multifida plants increased salt excretion (Na⁺ and Cl⁻) by leaves at 100 and 200 mM NaCl and leaf succulence at 60, 100, and 200 mM NaCl. Excessive accumulation of Na⁺ and Cl⁻ was avoided by shedding leaves. Our results indicate that L. multifida is better adapted to salinity compared to other members of the Lamiaceae ¸ a consideration that is particularly relevant for their growth in arid saline areas.     

Physiological Response to Sodium Chloride of Wild Swiss Chard

ABSTRACT

The present work was aimed at determining the limits of tolerance to sodium chloride (NaCl) of a halophyte, Beta macrocarpa Guss (wild Swiss chard). Five week-old plants were cultivated with a nutritive solution to which was added 0, 100, 200, and 300 mM NaCl. Plants were harvested after four weeks of treatment. The growth (fresh and dry weight, leaf surface area, and leaf number), water contents, and the mineral composition (meq · g^?1 DW) of roots and leaves (reduced nitrogen (N), K⁺, Ca^{2 +}, Na⁺, Cl^?) were determined on individual plants. Results show that Beta macrocarpa can tolerate up to 200 mM NaCl. A significant decrease in biomass production (to 50% of control) was observed only for 300 mM NaCl. In the latter treatment, leaf mean surface area was 25% of control. The shoot-to-root ratio was not changed. Leaf hydration was not modified by salt treatment. This ability of the plant to maintain the hydric equilibrium of its leaves seemed associated with an efficient intracellular compartmentalization of Na⁺ and Cl^? ions. Salt treatment had little effect on N content (80% of control), but decreased significantly K⁺ and Ca^{2 +} contents. These three essential elements could be limiting for growth of leaves and roots of plants challenged by NaCl.     

Effects of NaCl and silicon on ion distribution in the roots,shoots and leaves of two alfalfa cultivars with different salt tolerance

Abstract

The effects of exogenous NaCl and silicon on ion distribution were investigated in two alfalfa (Medicago sativa. L.) cultivars: the high salt tolerant Zhongmu No. 1 and the low salt tolerant Defor. The cultivars were grown in a hydroponic system with a control (that had neither NaCl nor Si added), a Si treatment (1 mmol L^?1 Si), a NaCl treatment (120 mmol L^?1 NaCl), and a Si and NaCl treatment (120 mmol L^?1 NaCl + 1 mmol L^?1 Si). After 15 days of the NaCl and Si treatments, four plants of the cultivars were removed and divided into root, shoot and leaf parts for Na⁺, K⁺, Ca²⁺, Mg²⁺, Fe³⁺, Mn²⁺, Cu²⁺ and Zn²⁺ content measurements. Compared with the NaCl treatment, the added Si significantly decreased Na⁺ content in the roots, but notably increased K⁺ contents in the shoots and leaves of the high salt tolerant Zhongmu No.1 cultivar. Applying Si to both cultivars under NaCl stress did not significantly affect the Fe³⁺, Mg²⁺ and Zn²⁺ contents in the roots, shoots and leaves of Defor and the roots and shoots of Zhongmu No.1, but increased the Ca²⁺ content in the roots of Zhongmu No.1 and the Mn²⁺ contents in the shoots and leaves of both cultivars, while it decreased the Ca²⁺ and Cu²⁺ contents of the shoots and leaves of both cultivars under salt stress. Salt stress decreased the K⁺, Ca²⁺, Mg²⁺ and Cu²⁺ contents in plants, but significantly increased Zn²⁺ content in the roots, shoots and leaves and Mn²⁺ content in the shoots of both cultivars when Si was not applied. Thus, salt affects not only the macronutrient distribution but also the micronutrient distribution in alfalfa plants, while silicon could alter the distributions of Na⁺ and some trophic ions in the roots, shoots and leaves of plants to improve the salt tolerance.     

Effect of Exogenous Silicon on Ion Distribution of Tomato Plants Under Salt Stress

Seedlings of two tomato cultivars were exposed to 0, 50, or 100 mM sodium chlroide (NaCl) stress with or without silicon (Si) for 10 days, and leaf electrolyte leakage, root activity, plant growth, and ion sodium, potassium, calcium, and magnesium (Na⁺, K⁺, Ca²⁺, and Mg²⁺) contents were determined. No significant differences were observed in total biomass and the root/crown ratio of salt-stressed plants treated with exogenous Si, but leaf electrolyte leakage of both cultivars treated with 50 mM NaCl and Si was lower than that in the same salt treatment without Si. Root activities of both cultivars were significantly affected by treatment with NaCl and exogenous Si. Application of Si induced a significant decrease in Na⁺ content and increases in K⁺, Ca²⁺, and Mg²⁺ contents in leaves of plants treated with 50 mM NaCl, and consequently the K⁺/Na⁺ and Ca²⁺/Na⁺ ratios increased by at least two times. The effects of Si on the ion contents of the roots were not notable.     

CONTRIBUTION OF PROLINE AND INORGANIC SOLUTES TO OSMOTIC ADJUSTMENT IN COTTON UNDER SALT STRESS

Physiological responses to salt stress were investigated in two cotton (Gossypium hirsutum L.) cultivars (Pora and Guazuncho) grown hydroponically under various concentrations of NaCl. Dry matter partitioning, plant water relations, mineral composition and proline content were studied. Proline and inorganic solutes were measured to determine their relative contribution to osmotic adjustment. Both leaf water potential (Ψ_w) and osmotic potential (Ψ_s)decreased in response to NaCl levels. Although Ψ_wand Ψ_s decreased during salt stress, pressure potential Ψ_p remained between 0.5 to 0.7 MPa in control and all NaCl treatments, even under 200 mol m^?3 NaCl. Increased NaCl levels resulted in a significant decrease in root, shoot and leaf growth biomass. Root / shoot ratio increased in response to salt stress. The responses of both cultivars to NaCl stress were similar. Increasing salinity levels increased plant Na⁺ and Cl^?. Potassium level remained stable in the leaves and decreased in the roots with increasing salinity. Salinity decreased Ca²⁺ and Mg²⁺ concentrations in leaves but did not affect the root levels of these nutrients. The K/Na selectivity ratio was much greater in the saline treated plants than in the control plants. Osmotic adjustment of roots and leaves was predominantly due to Na⁺ and Cl^? accumulation; the contribution of proline to the osmotic adjustment seemed to be less important in these cotton cultivars.     

Growth,ion accumulation,and lipid composition of two olive genotypes under salinity 1

Olive (Olea europaea L cv. Leccino and cv. Frantoio) plants grown in aeroponic cultivation system were supplied with Hoagland solutions containing 0 and 150 mM NaCl for 4 weeks. Sodium (Na⁺), chloride (Cl^‐), and potassium (K⁺) concentration was measued on 15‐day‐old leaves and K⁺/Na⁺ selectivity ratio was calculated. Plant water relations were estimated on the same leaves by measuring leaf bulk water and osmotic potentials, and by calculating leaf turgor pressure. Root and leaf tissues were also analysed for lipid composition, estimating free sterol (FS), glycolipid (GL) and phospholipd (PL) content. The salt‐sensitive Leccino accumulated more Na⁺ and Cl^‐ in the leaves and showed a lower K⁺/Na⁺ selectivity ratio than the salt‐tolerant Frantoio. The FS/PL ratio and the content of GL (namely mono‐galactosyldiglyceride, MGDG) in the roots were related to the salt accumulation in the shoot. Salinity‐induced changes on root lipids were more important in Frantoio than in Leccino, indicating the specific role of the roots in salt exclusion mechanisms. Conversely the effect of salinity on leaf lipid composition was more important in the leaves of the salt‐sensitive Leccino.     

COMPARISON OF OSMOTIC REGULATION IN DEHYDRATION- AND SALINITY-STRESSED SUNFLOWER SEEDLINGS

Plant dry matter accumulation rate (DMAR), relative water content (RWC), electrolyte leakage percentage (ELP), chlorophyll content, osmotic adjustment ability (OAA), and osmotica accumulation in leaves of sunflower (Helianthus annuus L.) seedlings under different levels of dehydration and salinity stress induced by iso-osmotic PEG (polyethylene glycol) or sodium chloride (NaCl) were evaluated. Plants were subjected to four stress treatments for 10 days: ?0.44 MPa PEG6000, ?0.44 MPa NaCl, ?0.88 MPa PEG6000, ?0.88 MPa NaCl. Results showed that PEG and NaCl treatments decreased the plant's DMAR and RWC, and NaCl treatments had more severe inhibitory effect on the plants than PEG treatments. Leaf ELP in sunflower seedlings increased after NaCl and PEG treatments. However, leaf ELP under salt stress was higher than that under dehydration stress (PEG treatment). All stress treatments increased OAA in plant leaves. Leaf OAA was enhanced significantly as PEG concentration increases, while leaf OAA was less enhanced at higher concentration of NaCl. OAA of sunflower leaves under dehydration stress was due to an increase in potassium (K⁺), calcium (Ca²⁺), amino acid, organic acid, magnesium (Mg²⁺), and proline content. OAA of sunflower leaves under moderate salt stress was owing to an increase in K⁺, chlorine (Cl^?), amino acid, organic acid, sodium (Na⁺), and proline content, and was mainly due to an accumulation of K⁺, Cl^?, Na⁺, and proline under severe salt stress.     

Growth response and ion homeostasis in two bermudagrass (Cynodon dactylon) cultivars differing in salinity tolerance under salinity stress

Bermudagrass (Cynodon dactylon) is a salinity-tolerant turfgrass that has good use potential in the saline-alkali lands of warm regions. However, the systematic Na⁺ and K⁺ regulation mechanisms under salinity stress remain unclear at the whole plant level. Two bermudagrass cultivars differing in salinity tolerance were exposed to 0, 50, 100, 200, or 300 mM NaCl in a hydroponic system. Growth, absorption, transportation, and secretion of Na⁺ and K⁺, and gas exchange parameters were determined in both cultivars. K⁺ contents were decreased and Na⁺ contents and Na⁺/K⁺ ratios were increased in both bermudagrasses with increased salinity; however, lower Na⁺ content and Na⁺/K⁺ ratio and more stable K⁺ content were found in the leaves of the salinity-tolerant ‘Yangjiang’ than the salinity-sensitive ‘Nanjing’. Higher Na⁺ contents in root cortical cells were found than in the stele cells of ‘Yangjiang’, but the opposite was observed in ‘Nanjing’. Lower Na⁺ contents and higher K⁺ contents were found in vessels for ‘Yangjiang’ than for ‘Nanjing’. Salinity stress increased the selective transport of K⁺ over Na⁺ from roots to leaves and the Na⁺-selective secretion via salt glands, which were stronger in ‘Yangjiang’ than ‘Nanjing’. Net photosynthetic rate and stomatal conductance decreased in the two bermudagrasses with increased salinity; however, they were more stable in ‘Yangjiang’. The results suggested that bermudagrass could reduce Na⁺ accumulation and maintain K⁺ stability in leaves under salinity stress by restricting Na⁺ into vessels in roots, selectively transporting K⁺ over Na⁺ from roots to leaves, selectively secreting Na⁺ via leaf salt glands, and maintaining suitable stomatal conductance.     

High K+ supply avoids Na+ toxicity and improves photosynthesis by allowing favorable K+ : Na+ ratios through the inhibition of Na+ uptake and transport to the shoots of Jatropha curcas plants

This study assessed the relationships between external K⁺ supply and K⁺ : Na⁺ ratios associated with Na⁺ toxicity in Jatropha curcas. Plants were exposed to increasing external K⁺ concentrations (6.25, 12.5, 25, 37.5, and 50 mM), combined with 50 mM NaCl in a nutrient solution. Photosynthesis progressively increased as the external K⁺ : Na⁺ ratios increased up to 0.75. The increase of photosynthesis and plant dry matter correlated positively with K⁺ : Na⁺ in xylem and leaves. The transport rates of K⁺ and Na⁺ from roots to xylem and leaves were inversely correlated. These ions presented an antagonistic pattern of accumulation in all organs. Maximum rates of photosynthesis and plant growth occurred with leaf K⁺ : Na⁺ ratios that ranged from 1.0 to 2.0, indicating that this parameter in leaves might be a good indicator for a favorable K⁺ homeostasis under salinity conditions. The higher K⁺ affinity and selectivity compared with Na⁺ in all organs associated with higher xylem flux and transport to shoots are essential for maintaining adequate K⁺ : Na⁺ ratios at the whole‐plant level. These characteristics, combined with adequate K⁺ concentrations, allow J. curcas to sustain high rates of photosynthesis and growth even under toxic NaCl levels.     

Time sequence studies on uptake and distribution of Na+ and Cl– in diplachne fusca (Kallar grass) grown in NaCl

Abstract

The time sequence of uptake and distribution of labelled Na and Cl^– in osmotically adjusted “Kallar”; grass was studied at low (10 mM) and moderately high salinity (100 mM) in nutrient solutions. Increasing NaCl raised the concentrations of Na⁺ and Cl^– in the tissue of tops and roots but had little or no effect on plant growth. On the leaves no toxic symptoms were obvious, not even in plants grown at salt stress of 200 mM NaCl. In all treatments, the young and the old leaves extruded 30–60% and 30–70% of their total Na⁺ and Cl^–. As the amounts of Na⁺ and Cl^– in the tissue increased with time, their extrusion also increased, however, as a proportion of the total Na⁺ and Cl^– it did not change much with time. Autoradiographs revealed that the extruded salts were distributed equally on the upper and lower surface of all leaves, parallel to veins. There seemed to be a more intense distribution of Na⁺ and Cl^– in the leaf sheaths as well as in the apical region of the roots. However, the net transfer rates, even after only 6 hours of uptake, did not indicate a strong retention mechanism in the roots.     

燕麦幼苗对氯化钠和氯化钾胁迫的生理响应差异

为探讨燕麦对NaCl和KCl胁迫的生理响应差异,采用水培法,研究了不同浓度NaCl和KCl胁迫对幼苗生长,活性氧代谢和渗透调节的影响。结果表明:(1)在75和150mmol/L浓度下,NaCl胁迫对燕麦幼苗的膜脂过氧化伤害和生长抑制大于KCl胁迫。NaCl胁迫下叶片中的超氧化物岐化酶(SOD),过氧化氢酶(CAT)活性及可溶性蛋白、可溶性糖和脯氨酸含量低于KCl胁迫;当浓度增大到225mmol/L时,KCl胁迫叶片中O-2.,H2O2,丙二醛(MDA),可溶性蛋白和可溶性糖含量显著大于NaCl胁迫,而SOD,抗坏血酸过氧化物酶(APX)活性及谷胱甘肽(GSH)含量则相反。(2)225mmol/L KCl和NaCl处理的植株叶片水势分别为-0.867和-1.034 MPa,渗透势分别为-1.409和-1.252 MPa,说明KCl对燕麦的更强伤害不是渗透胁迫所致;经225mmol/L KCl胁迫后,燕麦叶片中Na+含量下降至对照的36.5%,而K+含量上升为对照的1.49倍,而补充20mmol/L NaCl显著提高了225mmol/L KCl胁迫下叶片Na+的含量及SOD,APX活性,降低了K+,H2O2,O-2.和MDA含量,说明离子毒害引起的活性氧积累可能是高浓度KCl胁迫对燕麦幼苗伤害大于NaCl胁迫的重要原因。     

Effect of potassium on uptake and translocation of sodium and potassium in Chinese cabbage under NaCl stress

To investigate the influence of potassium (K⁺) on the salinity tolerance of Chinese cabbage (Brassica pekinensis Rupr.) seedlings, the plants were cultured at three K⁺ levels (0, 5, or 10?mM), under normal (0?mM NaCl) and high-salt (100?mM NaCl) conditions. The results indicated that the dry weight of Chinese cabbage increased with the application of K⁺ under salt stress. Addition of K⁺ increased K⁺ concentrations and suppressed sodium (Na⁺) concentration, which eventually increased the K⁺/Na⁺ ratios in roots or shoots. Application of K⁺ enhanced the uptake of K⁺ and suppressed the uptake of Na⁺. Moreover, the ratios of shoot-K⁺/root-K⁺ increased considerably, but the ratios of shoot-Na⁺/root-Na⁺ decreased in response to K⁺ application. It was concluded that the application of K⁺ could enhance the salt stress tolerance in Chinese cabbage because more K⁺ than Na⁺ was absorbed and translocated from roots to shoots.     

Does H+ pumping by plasmalemma ATPase limit leaf growth of maize (Zea mays) during the first phase of salt stress?

In the first phase of salt stress, growth of plants is impaired mainly by osmotic stress. To elucidate the effect of NaCl salinity on elongation growth of maize leaves in the first phase of salt stress, we investigated the effect of NaCl on gene expression and activity of the plasmalemma H⁺ ATPase of elongating leaves of maize (Zea mays L.). Treatment of maize plants with 125 mM NaCl for 3 d decreased leaf growth relative to control plants (1 mM NaCl). Whereas H⁺ ATPase hydrolytic activity was unaffected, the ability of the H⁺ ATPase to establish a pH gradient was strongly reduced. Total mRNA of plasmalemma H⁺ ATPase was slightly increased. However, mRNA of the ATPase isoform MHA1 was significantly reduced and ATPase isoform MHA4 was strongly increased at the mRNA level. Synthesis of total H⁺ ATPase protein was unchanged as revealed by western blot. The results indicate that reduced pumping of H⁺ ATPase in leaf plasmalemma under salt stress may be caused by a switch to gene expression of the specific isoform MHA4, which shows inferior H⁺‐pumping efficiency in comparison to isoforms expressed under control conditions. We propose that reduced H⁺ pumping of plasmalemma H⁺ ATPase is involved in the reduction of leaf growth of maize during the first phase of salt stress.     

Effect of different salts of sodium and potassium on the growth of Atriplex prostrata (Chenopodiaceae)

Although there are a variety of ions occurring in the soil throughout most of North America, the majority of halophyte literature focuses on the effects of NaCl on plants. In this study, a comparison is made of the effects of NaCl, KC1, Na₂SO₄, and K₂SO₄, on growth of the halophyte Atriplex prostrata Boucher ex DC (SYN: A. triangularis Willd.) at 0, ‐0.75, ‐1.00, and ‐1.50 MPa. Plant survival, height, number of leaves, nodes, and branches were recorded weekly. Photosynthesis was measured once before plants were harvested and dry mass was determined after one month. Content of Na⁺, K⁺,‐Mg²⁺, and Cl^‐ in plant tissue was also measured. A general trend observed was that all plant growth parameters decreased with a lowering of the medium osmotic potential, and that K⁺ salts were more inhibitory than Na⁺ salts. Ion content of plant tissue generally increased with a lowering of osmotic potential. Our data indicated that K⁺, a plant macronutrient, was more inhibitory to plant growth than Na⁺. It is possible that halophytes such as Atriplex prostrata could use Na⁺ as an osmoticum to adjust the vacuolar water potential, but were unable to use K⁺ for this function because of a specific ion toxicity. The inhibitory effect of salt on plant growth parameters and survival follow the pattern; K₂SO₄ >KCl>Na₂SO₄=NaCl.     

Puccinellia tenuiflora Exhibits Stronger Selectivity for K+ over Na+ than Wheat

Abstract

The characteristics of selectivity for K⁺ over Na⁺ by the roots of the halophyte Puccinellia tenuiflora were investigated in comparison with the glycophyte wheat (Triticum aestivum). Under various NaCl concentrations, the concentrations of K⁺ in the shoots of P. tenuiflora were 16–24% lower than those of wheat, whereas the concentrations of K⁺ in Puccinellia roots were 2.8–4.0 times higher than those of wheat. In 200 mM NaCl, the concentrations of Na⁺ in shoots of P. tenuiflora and wheat were similar under high K⁺ levels, but the concentrations of Na⁺ in wheat were 1.6 times higher than those in Puccinellia under low K⁺ levels. The concentrations of K⁺ in roots of P. tenuiflora were 1.5–2.0 times higher than those of wheat under low K⁺ levels. Formulas are given for calculating net selective absorption (SA) capacity and selective transport (ST) capacity by roots for K⁺ over Na⁺. We interpret SA as the net capacity of selectively absorbing K⁺ over Na⁺ by epidermal and cortical cells of whole plant roots into the root symplast. ST could reflect the net capacity of selection for K⁺ over Na⁺ transport from whole root stelar symplast to the xylem vessels. The lower ST value of P. tenuiflora might be the reason for accumulation of K⁺ in its roots. The SA values of P. tenuiflora and wheat were approximately equivalent in the low-affinity K⁺ uptake range. The SA values of the former were about two times higher than that of the latter in the high-affinity K⁺ uptake range, showing the root high-affinity K⁺ uptake system of the halophyte P. tenuiflora has a stronger capacity for K⁺ uptake.     

Salinity‐induced changes in growth,superoxide dismutase activity,and ion content of two olive cultivars

Olive trees (Olea europaea L.) are considered moderately tolerant to salinity, with clear differences found among cultivars. One‐year‐old self‐rooted olive plants of the Croatian cv. Oblica and Italian cv. Leccino were grown for 90 d in nutrient solutions containing 0, 66, or 166 mM NaCl, respectively. The shoot length and the number of nodes and leaves for both cultivars were not affected by salinity up to 66 mM NaCl. However, at 166 mM NaCl, growth of Leccino was reduced earlier and to a higher extent than growth of Oblica. After 10 d of exposure to 66 and 166 mM NaCl, increased activity of superoxide dismutase (SOD) was observed in Leccino, whereas there was almost no response in Oblica. Reduced SOD activity in Leccino at 166 mM NaCl was observed after prolonged stress (90 d), whereas in Oblica SOD was increased at 66 mM compared to control or 166 mM NaCl. Electrolyte and K⁺ leakage were increased and relative water content decreased as NaCl concentration increased with similar intensity of response measured in both cultivars. Oblica exhibited an ability to keep a higher K⁺ : Na⁺ ratio at all salinity levels compared to Leccino, but since no difference was found in leaf K⁺ concentration, this was mainly achieved by less Na⁺ ions reaching the younger leaves. The antioxidative system represents a component of the complex olive salt‐tolerance mechanism, and it seems that the role of SOD in protection from oxidative stress depends on sodium accumulation in leaves.