Mechanisms of salt stress tolerance in two rose rootstocks: Rosa chinensis ‘Major’ and R. rubiginosa

The responses of two rose rootstocks Rosa chinensis ‘Major’ and R. rubiginosa were investigated under salt stress. The distribution of chloride and sodium ions in all plant parts was determined. The salt treatments were applied through irrigation water containing 0, 5, 10, 20 and 30 mM NaCl. Necrosis on the leaves as a result of the NaCl treatments was observed with in rootstocks after two months. Leaf injury was more pronounced in R. chinensis ‘Major’ than R. rubiginosa. The rootstock R. rubiginosa showed a higher tolerance to the NaCl stress than R. chinensis ‘Major’. The survival of the plants under increased NaCl stress as well as the extent of leaf injury could be used in the determination of tolerance of the rose genotypes. The lower older leaves contained higher concentrations of Cl⁻ than the young upper leaves. Leaf samples had higher concentrations of Cl⁻ than stem samples taken from the same positions. The roots contained higher amounts of Cl⁻ than the stem samples. The plants accumulated higher amounts of Cl⁻ in comparison with Na⁺. The lower leaves of R. chinensis ‘Major’ had higher amounts of Na⁺ than in all other parts whereas R. rubiginosa had higher concentrations of Na⁺ in the roots than in all other parts.     

The effects of sodium chloride on ornamental shrubs

The use of saline waters is an option for the irrigation of salt tolerant ornamentals as competition for high quality water increases. However, despite the importance of ornamental shrubs in Mediterranean areas, salt tolerance of such species has received little attention. The aims of our investigation were to quantify the growth response and any injury symptom of 12 widely cultivated ornamental shrubs to irrigation with saline water and to investigate any possible relation with the concentration of Na⁺ and Cl⁻ in the plants. Species were irrigated with different salinities (10, 40, and 70 mM NaCl) for a 120-day period. At the end of salt treatment, plants were sampled and dry biomass recorded; the relative growth rate (RGR) was also calculated. Root and leaf samples from each species were used to evaluate Na⁺, K⁺ and Cl⁻ concentrations. Growth rates were significantly reduced in Cotoneaster lacteus, Grevillea juniperina and Pyracantha ‘Harlequin’, which also showed the highest percentage of necrotic leaves. The increasing external NaCl lead to an increase of Na⁺ and Cl⁻ in roots and leaves of the different species, although less Na⁺ was accumulated than Cl⁻: growth reduction well correlated with the concentration of Cl⁻ and/or Na⁺ in the leaves. The most sensitive species (i.e. C. lacteus, G. juniperina and Pyracantha ‘Harlequin’) had high concentrations of Na⁺ and/or Cl⁻ in their leaves and also showed a decrease in their leaf K⁺/Na⁺ ratios. Even though other species (i.e. Bougainvillea glabra, Ceanothus thyrsiflorus, Leptospermum scoparium, Leucophyllum frutescens and Ruttya fruticosa) demonstrated a high ion concentration in their leaves, they could be considered relatively salt tolerant as there was little growth reduction and few symptoms of injury in the leaves. In some other cases (i.e. Cestrum fasciculatum, Escallonia rubra and Viburnum lucidum) the observed tolerance was related to higher ion concentration in the roots compared to the leaves, probably indicative of a limited transport to the shoots. Only in Eugenia myrtifolia was the absence of symptoms associated with a limited Na⁺ and Cl⁻ uptake from the rhizosphere.     

Comparison of growth,leaf water relations and gas exchange of Cistus albidus and C. monspeliensis plants irrigated with water of different NaCl salinity levels

Four-month-old potted Cistus albidus and Cistus monspeliensis plants growing in a greenhouse were submitted to saline stress from 9 August to 2 December, using irrigation water containing 0, 70, and 140 mM NaCl. C. monspeliensis plants are more tolerant to saline irrigation water than C. albidus plants, mainly due to their capacity to resist stress with a lower plant biomass and canopy area; furthermore, they showed no leaf necrosis symptoms. Under saline stress conditions the main growth limiting factor in both species was photosynthesis. Both Cistus species responded to saline stress by developing avoidance and tolerance mechanisms. The avoidance mechanisms took place at a morphological and physiological level. Morphologically, the reduction in the canopy area can be considered a mechanisms for regulating water loss via transpiration. Treated C. monspeliensis plants showed a greater capacity to absorb water and were able to conserve it more efficiently than C. albidus plants. Tolerance mechanisms included Na⁺ and Cl⁻ inclusion and osmotic adjustment. However, the reaction of each species to osmotic adjustment was different, because in C. monspeliensis plants the osmotic adjustment was unable to prevent a decrease in leaf turgor. The curvilinear relationship between P_n and g_l observed in C. monspeliensis plants indicated stomatal limitation of photosynthesis below a leaf conductance of about 160 mmol m⁻² s⁻¹. In C. albidus plants, a linear relationship between photosynthesis and leaf conductance rather a curvilinear model was significant, indicating limitation of the photosynthetic capacity.     

Effects of Stockosorb and Luquasorb polymers on salt and drought tolerance of Populus popularis

The effects of two types of hydrophilic polymers on drought and salt resistance of 1-year-old cuttings of Populus popularis 35–44 were investigated in this study. The polymers used in the experiments were Stockosorb 500 XL (Stockosorb) (a granular type, cross-linked poly potassium-co-(acrylic resin polymer)-co-polyacrylamide hydrogel) and Luquasorb^® product (a powder type of potassium polyacrylate), which were manufactured by Stockhausen GmbH Krefeld and BASF Corporation in Germany, respectively. Drought or salt stress significantly decreased leaf photosynthesis and transpiration, as well as plant water-consumption and dry weight. A significant reduction occurred in Drought + NaCl-stressed plants. Soils treated by 0.5% Stockosorb or Luquasorb markedly alleviated the inhibition of plant growth and leaf gas-exchange that were caused by drought and/or salt stress treatments, and the occurrence of stress-induced leaf injury was delayed for 31 and 51 days, respectively. Experimental results showed that hydrophilic polymers in root media assisted P. popularis plants to tolerate the drought and salt stresses, due to the following reasons: (1) roots took up the retained water from hydrophilic polymers when water was deficient in the soil (Stockosorb-treated plants exhibited a higher rate of water uptake); (2) under saline conditions, Stockosorb and Luquasorb held Na⁺ and Cl⁻ in the soil solution due to their high water-holding capacity, thus limiting an excessive accumulation of toxic ions in the plant organs; furthermore, the exchangeable K⁺ that contained in Stockosorb and Luquasorb resulted in an improved K⁺/Na⁺ homeostasis in salinized plants; (3) hydrophilic polymers aided the plants to tolerate an interactive impacts of drought and salt stresses, which was mainly accounted for their water- and salt-holding capacities. In comparison, the growth and survival enhancement effects of the hydrophilic polymers on Drought + NaCl-treated plants was more evident by Luquasorb application, because it supplied water to plants at a lower rate during soil drying, thus prolonging the duration of water supply and allowed roots to grow in an environment of lower salinity for a long period of salt and drought stresses.     

Irrigation of Myrtus communis plants with reclaimed water: morphological and physiological responses to different levels of salinity

Summary

The influence of irrigation with different sources of reclaimed water on physiological and morphological changes in Myrtus communis plants was investigated to evaluate their adaptability to such conditions. M. communis plants, growing in a growth chamber, were subjected to four irrigation treatments over 4 months (120 d): a control [tap water (0.8 dS m^–1), leaching 10% (v/v) of the applied water] and three reclaimed water irrigation treatments, namely 1.5 dS m^–1 leaching 25% (v/v) of the applied water (RW1), 4.0 dS m^–1 leaching 40% (v/v) of the applied water (RW2), and 8.0 dS m^–1 leaching 55% (v/v) of the applied water (RW3). After treatment, all plants were irrigated with tap water, as for the control plants, for a further 2 months (60 d). At the end of the first period (4 months), none of the myrtle plants showed any adverse change in biomass and the average total dry weight (DW) increased by 53% in treatment RW2. However, at the end of the treatment and recovery period (180 d), accumulations of Cl^– ions, and especially Na⁺ ions, negatively affected the growth of all RW3 plants. Plants irrigated with all three reclaimed water samples had increased difficulty in taking-up water from the substrate (i.e., they had lower leaf water potential and relative water content values). RW2 plants showed a better response in their gas exchange parameters. The use of reclaimed water decreased leaf K⁺/Na⁺ and Ca²⁺/Na⁺ ratios, but no chlorosis or necrosis were observed. The three reclaimed water samples had different effects on the myrtle plants depending on the specific chemical properties of the water. Leaching was found to be important to minimise the negative effects of salinity in the irrigation water.     

Physiological responses and adaptive strategies of tomato plants to salt and alkali stresses

In this study, seedlings of tomato were treated with salt stress or alkali stress. The growth, photosynthesis and concentrations of solutes and inorganic ions in tissue sap of stressed seedlings were measured to investigate the physiological adaptive mechanisms by which tomato tolerates alkali stress. The alkali stress clearly inhibited growth and photosynthesis. With increasing salinity, the Na⁺ concentration and Na⁺/K⁺ ratio in leaves increased, with greater degrees of increase under alkali than under salt stress. This indicated that high-pH caused by alkali stress might affect the control of roots on Na⁺ uptake and increased the intracellular Na⁺ to a toxic level, which might be the main cause of reductions of stomatal conductance and net photosynthetic rates under alkali stress. Under salt stress, organic acids (OAs), Na⁺, K⁺ and Cl⁻ were the main osmolytes in both roots and leaves. Under alkali stress, roots and leaves revealed different mechanisms of ion balance and osmotic regulation. Under alkali stress, in roots, OAs and Na⁺ were the main osmolytes, and the osmotic role of K⁺ was small; however, in leaves, OAs, Na⁺ and K⁺ all played important osmotic roles. The mechanisms governing ionic balance under both stresses were different. Under salt stress, the contribution of inorganic ions to keep ion balance was greater than that of OAs. However, under alkali stress, Cl⁻, H₂PO₄⁻ and SO₄²⁻ concentrations decreased, and tomato might have enhanced OA synthesis to compensate for the shortage of inorganic anions.     

Effects of Ascorbic Acid and Reduced Glutathione on the Alleviation of Salinity Stress in Olive Plants

The aim of this study was to evaluate the effects of low molecular mass antioxidants and NaCl salinity on growth, ionic balance, proline, and water contents of ‘Zard’ olive trees under controlled greenhouse conditions. The experiment was carried out by spraying 2 mM of ascorbic acid (Asc) and 3 mM of reduced glutathione (GSH) on the plants that were treated with two salinity levels (0 and 100 mM NaCl) on their root medium. Plant growth parameters (leaf fresh weight, leaf dry weight, leaf number, total fresh weight, and total dry weight) were significantly improved by Asc compared with growth parameters in GSH and control plants. Higher concentrations of Na⁺ and Cl^– were observed in salt-stressed plants, while Na⁺ and Cl^– concentrations were decreased in the olive leaves that were sprayed with Asc. Salinity in the root zone caused a considerable decline in both K⁺ concentration and K/Na ratio. K⁺ concentration and K/Na ratio were significantly increased by application of Asc on plant leaves. Salinity caused an increase in electrolyte leakage (EL) compared with the control plants. Lowest EL and tissue water content (TWC) was obtained in Asc-sprayed plants, whereas TWC was increased in salt-stressed plants. Plants were subjected to salt stress and showed a higher relative water content (RWC) than the control plants. Salt stress induced proline accumulation in olive leaves. In conclusion, exogenous application of Asc is recommended to improve tolerance of olive plants under saline conditions.     

Orange varieties as interstocks increase the salt tolerance of lemon trees

Summary

We investigated the ability of interstocks to increase salt tolerance in lemon trees. We compared 2-year-old ‘Verna’ lemon trees [Citrus limon (L.) Burm.; VL] grafted on Sour Orange (C. aurantium L.; SO) rootstock either without an interstock (VL/SO), or interstocked with ‘Valencia’ orange (C. sinensis Osbeck; VL/V/SO), or with ‘Castellano’ orange (C. sinensis Osbeck; VL/C/SO). Trees were grown under greenhouse conditions and supplied with nutrient solutions containing 0, 30, or 60 mM NaCl. Reductions in leaf growth caused by salt treatment were greatest in non-interstocked (VL/SO) trees, followed by VL/C/SO trees, and were the least in VL/V/SO trees. Although the levels of Cl^? and Na⁺ ions in the roots and stems were not affected by either interstock, leaf concentrations of Cl^? and Na⁺ were higher in VL/SO trees than in VL/C/SO or VL/V/SO trees, suggesting that an interstock in Citrus trees could limit the uptake and transport of such ions to the shoots. Saline-treated VL/SO trees also tended to have the lowest shoot:root (S:R) ratios; so, overall, there was a negative relationship between S:R ratio and leaf Cl- ion concentration. Leaf transpiration (E_leaf) may also be involved in the reduction in leaf Cl^? concentration, as interstocked trees had lower E_leaf values at mid-day than non-interstocked trees. Salinity increased leaf concentrations of Ca²⁺ in VL/C/SO trees and increased both leaf K⁺ and N concentrations in all trees, regardless of interstock. Salinity reduced leaf water potentials and osmotic potentials, such that leaf turgor was increased in all trees.     

Assessment of tolerance to NaCl salinity of five olive cultivars,based on growth characteristics and Na and Cl exclusion mechanisms

Changes caused by NaCl-induced salinity on several growth parameters and ions accumulation have been measured in five olive (Olea europaea L.) cultivars (‘Chemlali’, ‘Chetoui’, ‘Koroneiki’, ‘Arbequina I18’, and ‘Arbosana I43’) growing in a greenhouse in nutrient solution pot experiment. One-year-old plants were transplanted to sand–perlite (1:1) culture, and were irrigated with half-strength Hoagland nutrient solution containing NaCl at various levels (0.5, 50, 100 and 200 mM). Salinity induced significant decrease in growth parameters, but to a different extent in each cultivar. Leaf growth and total leaf area per plant were significantly affected by all salinity treatments in all studied cultivars, being ‘Arbequina I18’ the most sensitive cultivar. Leaf drop phenomenon was observed from 60 days after salt application at high salinity treatments, mainly in Arbequina I18. Contrary to leaf area, leaf thickness increased progressively during the experiment. ‘Chemlali’ developed thicker leaves at the two highest salinity treatments when compared to the other cultivars. Na⁺ and Cl⁻ concentrations were higher in roots than in shoots and leaves in most of the cultivars investigated. The effectiveness of Na⁺ exclusion mechanism in the roots differed significantly among studied cultivars, working effectively in ‘Chemlali’ (by inhibiting translocation of Na⁺ to the aerial part) and being much less efficient in ‘Arbequina I18’. Furthermore, leaf abscission can be considered as an additional tolerance mechanism of olive cultivars allowing the elimination of leaves that had accumulated Na⁺ and Cl⁻ ions. Tolerance to salinity stress was as follows: ‘Chemlali’ > ‘Chetoui’ > ‘Arbosana I43’ > ‘Koroneiki’ > ‘Arbequina I18’. This order of salt tolerance was indicated by lower reduction in plant growth parameters (shoot elongation, trunk diameter, total plant dry weight, internodes length, and total leaf area), the increase of leaf thickness, and by the effectiveness of the exclusion mechanism of Na⁺ and Cl⁻ in the root system.     

Alleviation of salt-induced adverse effects in eggplant (Solanum melongena L.) by glycinebetaine and sugarbeet extracts

Two eggplant cultivars, Dilnasheen and Bemisal, were selected to assess whether pure GB and sugarbeet extract could effectively ameliorate the harmful effects of salt stress on eggplant (Solanum melongena L.), under saline conditions. Salt stress markedly suppressed the growth, yield, photosynthetic capacity, internal CO₂ level, transpiration, and stomatal conductance in both cultivars. Potassium (K⁺) and Ca²⁺ contents and K⁺/Na⁺ ratios of both root and leaf were also reduced, while GB and proline in leaves, and Na⁺ and Cl⁻ contents in roots and leaves were significantly enhanced. Exogenously applied glycinebetaine and sugarbeet extracts significantly counteracted the salt-induced adverse effects on growth, yield, various gas exchange characteristics, GB and leaf K⁺, Ca⁺, Cl⁻ and Na⁺. However, GB and sugarbeet extract showed differential effects on photosynthetic rate, stomatal conductance and transpiration, internal CO₂ level, C_i/C_a ratio, leaf K⁺, Ca²⁺, and Cl⁻ contents, and K⁺/Na⁺ ratio. Sugarbeet extract proved better than the GB in improving growth, photosynthetic rate, transpiration, stomatal conductance, yield and GB accumulation. Since, sugarbeet extract contains a substantial amount of GB along with a variety of other important nutrients so it was found as effective as pure GB in improving growth and some key physiological processes in eggplant under salt stress. Thus, it can be used as an alternative cheaper source of GB for its use as an ameliorative agent for protecting plants against the hazardous effects of salt stress.     

Calcium starvation increases salt susceptibility in olive plants but has no effect on susceptibility to water stress

Summary

The responses of leaf water status, growth, and ion concentrations to water or to saline stresses were compared in olive cuttings of different Ca²⁺ status. Mist-rooted ‘Picual’ olive cuttings were grown in a greenhouse in 2 l plastic pots containing perlite. A nutrient solution with or without 2.5 mM CaCl₂ was initially used to irrigate the plants. When the Ca²⁺-starved plants differed in height from the Ca²⁺-treated plants, water or saline stress (i.e., no irrigation or 75 mM NaCl, respectively) were applied. The results indicated that Ca²⁺ increased growth in saline-treated plants, but not in water-stressed plants. After 98 d growth, the stresses were relieved and the plants were irrigated again with or without Ca²⁺. Growth increased and leaf water status was increased during this recovery period, but no direct effects of Ca²⁺ were observed in the response of plants to stress-relief. We suggest that the beneficial effect of Ca²⁺ on tolerance to salt stress in olive plants was related to protection against Na⁺ toxicity, because there was no response of water-stressed plants to the supply of Ca²⁺.     

Fruits are more sensitive to salinity than leaves and stems in pepper plants (Capsicum annuum L.)

The effects of NaCl stress on plant growth, gas-exchange, activity of superoxide dismutase (SOD), rate of lipid peroxidation, and accumulation of Na⁺ ion and sugar were investigated in leaves and fruits of pepper plants (Capsicum annuum L.). Especially, the gene expression of l-galactono-1,4-lactone dehydrogenase (GalLDH), which is the last enzyme of ascorbic acid (AsA) biosynthesis, and the relationships between AsA level and Na⁺ concentration in plant tissue were investigated with increasing salinity. Plants were treated with three treatments: the control (0 mM NaCl) and two salinity levels (50 and 100 mM NaCl) for 21 days under greenhouse conditions. Plant growth was markedly restricted due to the reduction of photosynthetic rate and the increase of Na⁺ accumulation in leaves with the increasing intensity of NaCl stress. Salinity had more effect on fruit growth comparing to leaf growth, suggesting that fruits could be more sensitive to salinity than leaves. In comparison with the control, salt stress significantly increased lipid peroxidation (as measured as malondialdehyde content) but decreased SOD activity in both fruits and leaves although the effect was larger in fruits; and the rate of the decrease in SOD activity was greater than that of the increase in lipid peroxidation. The AsA concentration transiently increased first 7 days but it slightly decreased from the initial level in the end of treatment day 21. The change in GalLDH gene expression was similar to AsA concentration. The accumulation of Na⁺, the reduction of AsA level at severe salinity stress were greater in fruits than in leaves; and AsA level had a negative relationship with Na⁺ concentration in both leaves and fruits. These results suggest that the difference in salt sensitivity between fruits and leaves in pepper plants can be related to the difference in inhibition of AsA synthesis, which in turn is probably due to the toxicity of extreme accumulation of Na⁺.     

Improving the fruit yield and quality of cucumber by grafting onto the salt tolerant rootstock under NaCl stress

To investigate the feasibility of using salt tolerant rootstock to increase fruit yield and quality of cucumber under NaCl stress, a greenhouse experiment was carried out to determine fruit yield, leaf relative water content, fruit quality, and mineral composition of cucumber plants (Cucumis sativus L. cv. Jinchun No. 2), either self-grafted or grafted onto the commercial salt tolerant rootstock Figleaf Gourd (Cucurbita ficifolia Bouche) and Chaofeng Kangshengwang (Lagenaria siceraria Standl). Plants were grown in a substrate culture (peat:vermiculite:perlite = 1:1:1, v/v) and irrigated with half-strength Hoagland solutions containing 0, 30, or 60 mM NaCl. The results showed that salinity significantly reduced fruit yield of cucumber owing to a decrease both in mean fruit weight and fruit number. Rootstock had no significant effect on leaf relative water content. Plants grafted onto Figleaf Gourd and Chaofeng Kangshengwang had higher fruit number, marketable and total fruit yield than those of self-grafted plants under 0, 30, and 60 mM NaCl, which could be attributed to, at least in part, the higher K⁺ but lower Na⁺ and/or Cl⁻ contents in the leaves. Salinity improved fruit quality by increasing fruit dry matter, soluble sugar, and titratable acidity contents of all the plants, but had no significant effect on vitamin C content. In comparison to the self-grafted plants, plants grafted onto Figleaf Gourd and Chaofeng Kangshengwang had an overall improved fruit quality under NaCl stress owing to an increase in contents of soluble sugar, titratable acidity, and vitamin C, and a decrease in the percentage of non-marketable fruit and Na⁺ and/or Cl⁻ contents of fruits in comparison to the self-grafted plants, mainly under 60 mM NaCl. Overall, it is suggested that the use of salt tolerant rootstock could provide a useful tool to improve fruit yield and quality of cucumber under NaCl stress.     

Comparison of the responses to NaCl stress of two pea cultivars using split-root system

Two pea (Pisum sativum L.) cultivars were compared: cv Lincoln and cv Douce de Provence. Seedlings grown for 14 d on standard medium were challenged for 21 d with salt using a split-root system. This protocol allowed salt-treated plants to absorb nutrients through a part of their root system maintained in control medium (C), the other part of the root system being placed in medium added with 75 mM NaCl (S). Full salt treatment (S/S) resulted in severe but non-lethal growth inhibition, high concentration of Na⁺ and Cl⁻ in leaves, and decrease in leaf K⁺ and chlorophyll contents. The two latter effects were more pronounced in Lincoln than in D. Provence. Growth inhibition was partially (Lincoln) or totally (D. Provence) alleviated in S/C configuration, and K⁺ content was less diminished than in full salt treatment. S/C treatment mitigated Na⁺ and Cl⁻ accumulation in Lincoln, but not in D. Provence. Thus, in the latter cultivar, growth inhibition by salt in S/S condition likely did not result from excessive Na⁺ and Cl⁻ accumulation in leaves. Increased electrolyte leakage from leaf tissues evidenced damages to leaf cell plasma membrane of both cultivars in S/S condition. However, damages to chloroplasts, as inferred from chlorophyll loss, were much pronounced in Lincoln than in D. Provence. Antioxidant enzymic activities in leaves were measured as proxies for oxidative stress. Catalase activity was stimulated by S/S treatment in both cultivars, but superoxide dismutase (Fe and Cu/Zn isoforms) and gaiacol peroxidase activities were augmented only in Lincoln. The absence of superoxide dismutase activity stimulation by salt in D. Provence could signify either that constitutive activity was sufficient to ensure protection against oxidative stress, or that intrinsic salt tolerance of this cultivar mitigated cellular oxidative stress. Thus, intraspecific variability for salt response exists between pea cultivars presenting similar growth sensitivity to salt.     

Growth, photosynthesis and antioxidant metabolism in mustard (Brassica juncea L.) cultivars differing in ATP-sulfurylase activity under salinity stress

Salinity is one of the major environmental factors limiting crop productivity. The effect of increasing salinity levels (0, 50, 100 mM NaCl) on growth, photosynthetic traits, leaf water potential, oxidative stress, enzymatic and non-enzymatic antioxidants was studied in Pusa Jai Kisan and SS2 cultivars of mustard (Brassica juncea L. Czern & Coss.) differing in ATP-sulfurylase activity at 30 days after sowing (DAS). The cultivar SS2 (low ATP-sulfurylase activity) accumulated higher content of Na⁺ and Cl⁻ in leaf than root. SS2 also showed greater content of thiobarbituric acid reactive substances (TBARS) and H₂O₂ and higher decrease in growth, photosynthetic traits and leaf water potential than Pusa Jai Kisan with increasing salinity levels. Contrarily, Pusa Jai Kisan (high ATP-sulfurylase activity) exhibited higher Na⁺ and Cl⁻ content in root than leaf, lower TBARS and H₂O₂ content and higher activity of catalase, ascorbate peroxidase and glutathione reductase. However, the activity of superoxide dismutase was greater in SS2 than Pusa Jai Kisan. Higher activity of ATP-sulfurylase in Pusa Jai Kisan resulted in increased content of glutathione, a reduced form of inorganic sulfur and an essential component of cellular antioxidant defense system. The lesser decrease in growth and photosynthesis in Pusa Jai Kisan was the result of lesser Na⁺ and Cl⁻ in leaf, higher turgidity and increased activity of antioxidant enzymes and glutathione content.     

Additional nitrogen fertilization affects salt tolerance of lemon trees on different rootstocks

Irrigation with saline water is one of the major problems in citrus crop in arid and semi-arid regions. Because rootstock and fertilization play an important role in citrus salt tolerance, we investigated the influence of the nitrogen fertilization and rootstock on salt tolerance of 2-year-old potted Fino 49 lemon trees. For that, trees grafted on Citrus macrophylla (M) or Sour orange (SO) rootstocks were watered for 12 weeks with complete nutrient solution containing either 0 mM NaCl (control, C), 50 mM NaCl (S), 50 mM NaCl with an additional 10 mM potassium nitrate (S + N), or 50 mM NaCl with a 1% KNO₃ (S + Nf) foliar spray application. Trees on M were more vigorous than trees on SO and saline treatments reduced leaf growth similarly in trees on both rootstocks. Trees on SO had a lower leaf Cl⁻ and Na⁺ concentration than those on M. Additional soil nitrogen (S + N) decreased leaf Cl⁻ concentration and increased leaf K⁺ concentration in salinized trees on both rootstocks. However, the salinity-induced reduction leaf growth was similar in S + N and S trees. This was due to osmotic effect, beside leaf Cl⁻ and Na⁺ toxicity, played an important role in the growth response of Fino 49 lemon to the salt stress. Additional foliar nitrogen in the S + Nf treatment also reduced leaf Cl⁻ concentration relative to the S treatment but trees from S + Nf treatment had the lowest leaf growth. Net assimilation of CO₂ (ACO₂$A_{\text{C}{\text{O}}_2}$), stomatal conductance (g_s) and plant transpiration were reduced similarly in all three salt treatments, regardless rootstock. Salinity reduced leaf water and osmotic potential such that leaf turgor was increased. Thus, the salinity-induced ACO₂$A_{\text{C}{\text{O}}_2}$ reductions were not due to loss of turgor but rather due to high salt ion accumulation in leaves.     

Comparative salt responses at cell and whole-plant levels of cultivated and wild tomato species and their hybrid

SUMMARY

Response to increased salinity was compared in whole plants and calli from leaf, stem and root of Lycopersicon esculentum Mill. cv. P-73, Lycopersicon pennellii (Correll) D'Arcy ac PE-47 and their interspecific hybrid. Three NaCl treatments were applied (0, 70 and 140 raM) for 28 d. In both calli and whole plants, L. pennellii was more salt-tolerant than the cultivated species and the hybrid according to the growth responses, although different degrees of salt tolerance were generally found between plants and calli. The Na⁺ and CI" accumulations with salinity were higher in L. pennellii than in L. esculentum at both levels oforganization. The interspecific hybrid showed an accumulation ability for Na⁺ and CI^" intermediate to its parents in the shoot of the whole plants and similar to L. pennellii in the callus tissues. Either no decrease or a small decrease of K⁺ concentrations with salinity were found in both whole plants and callus tissues of L. esculentum. However, K⁺ concentrations decreased in the organs and calli of L. pennellii and the hybrid with increasing salinity. Only at the whole plant level did L. pennellii have a Na7K⁺ ratio higher than L. esculentum, showing the hybrid to have values between those of its parents in the shoot.     

Growth,biomass allocation and leaf ion concentration of seven olive (Olea europaea L.) cultivars under increased salinity

Olive (Olea europaea L.) is the major fruit tree in the Mediterranean region, often grown in locations where plants are exposed to increased salinity. To determine the effect of NaCl on shoot and root growth, dry matter allocation, leaf Na⁺ and K⁺ concentration, electrolyte (EL) and K⁺ leakage (KL), seven olive cultivars of different origins were grown in nutrient solution containing 0, 33, 66, 100 or 166 mM NaCl for three months. The general effect of salinity was linear and quadratic decrease of observed plant growth parameters. Different responses of tested cultivars to applied levels of salinity were found for stem dry weight, shoot length and number of leaves. As salinity increased, growth of ‘Manzanillo’ declined sharply, whereas ‘Frantoio’ was the most tolerant to growth reduction in most of the observed growth parameters. Allometric analysis showed that biomass allocation under salinity stress was similar in all cultivars, but the slope between shoot weight and total plant weight decreased as salinity increased. Since the higher allocation in roots was not found, it seems that salinity only slowed the above ground plant canopy growth. Sodium concentration in leaves of all cultivars increased as salinity increased with the highest increment reached when the salinity of nutrient solution was raised from 100 to 166 mM NaCl. Significant differences among genotypes were found in leaf Na⁺ and K⁺ concentration and K⁺:Na⁺ ratio, but they were not related to the growth rate. Generally, ‘Frantoio’ and ‘Oblica’ accumulated less Na⁺ and were able to maintain higher K⁺:Na⁺ ratios as compared to other genotypes. Electrolyte leakage and KL linearly increased with increasing salinity and the magnitude of the response depended upon the olive cultivar.     

Growth responses and ion regulation of four warm season turfgrasses to long-term salinity stress

Increased need for salinity tolerant turfgrasses continues due to increased use of saline water for lawn irrigation and turfgrass establishment on highly saline soil in arid and seashore regions. Turfgrasses growing on saline soil suffer from long-term salinity stress, so this experiment was conducted to study the salinity tolerance, growth, and physiological responses of four warm season turfgrasses [including ‘Diamond’ zoysiagrass (Zoysia matrella (L.) Merr.), ‘Z080’ zoysiagrass (Z. japonica Steud.), ‘C291’ bermudagrass (Cynodon dactylon (L.) Pers), and ‘Adalayd’ seashore paspalum (Paspalum vaginatum Sw.)] to 9 months of salinity stress. Seven salinity levels of irrigation water (0, 90, 180, 360, 540, 720, and 900 mM NaCl) were applied to turfgrasses grown in plastic tubes in a glass room. The salinity tolerance decreased in the following order according to percent green leaf canopy area after 9 months of salinity treatments: ‘Diamond’ > ‘Adalayd’ > ‘C291’ > ‘Z080’. Leaf weight, leaf length, canopy height, shoot density were significantly affected by salinity treatments for all turfgrasses. However, leaf width and/or leaf number per shoot were not affected by salinity in all turfgrasses except ‘Diamond’. Leaf and/or root water contents were also little affected. As salinity increased, leaf and root Na⁺ concentrations and Na⁺/K⁺ rates increased significantly and K⁺ concentrations decreased significantly except that of ‘Adalayd’ leaf. ‘Diamond’ and ‘Z080’ could reduce Na⁺ accumulation in the leaves by salt secretion from salt glands, while ‘Adalayd’ could exclude Na⁺ from the leaves and accumulate K⁺ in the leaves. ‘C291’ exhibited both ion regulation mechanisms, but to much less extent. Different growth responses and ion regulation means of four turfgrasses reflected different salinity tolerance mechanisms.     

Ameliorative effects of biological treatments on growth of squash plants under salt stress

The objective of this work was to evaluate the effect of selected biologicals on direct seeded and transplanted squash plant growth and mineral content under salinity stress. The study was conducted in pot experiments using a mixture of sandy loam soil:vermiculite (1:1, v:v) under controlled greenhouse conditions. Biologicals tested included AgBlend, SoilBuilder, Yield Shield, PlantShield, Inoculaid and Equity. Salinity treatments were established by adding 0, 50 and 100 mM of NaCl to a base complete nutrient solution (Hydro-Sol + Ca(NO₃)₂). Pots were irrigated with NaCl solutions and biological treatments were included in the water. Yield Shield was applied as a seed treatment. Salinity negatively affected growth of squash; however, biological treatments significantly increased fresh weight compared to non-treated plants that were challenged with salt stress. Furthermore, biological treatments tested increased the uptake of potassium compared to the non-treated control in both direct seeded and transplanted squash. Sodium concentration was not affected by biologicals in directed seeded squash except for SoilBuilder, Yield Shield and Equity at 100 mM, while AgBlend, SoilBuilder, Inoculaid and Equity decreased sodium uptake in transplants under salt stress. The most effective biologicals increased the K⁺/Na⁺ ratio, which was positively correlated with plant growth. Alteration of mineral uptake may be one mechanism for the alleviation of salt stress. Based on the results of the experiment reported herein, the use of biological treatments may provide a means of facilitating plant growth under salt stress.