Different antioxidant responses to salt stress in two different provenances of <Emphasis Type="Italic">Carthamus tinctorius</Emphasis> L.

Seedlings of two Tunisian Carthamus tinctorius L. provenances (Kairouan and Tazarka) differing in salt sensitivity were hydroponically grown at 0 and 50 mM NaCl over 21 days. Leaves of Kairouan (salt-sensitive) showed a 48% restriction in their growth at 50 mM NaCl although they accumulated less sodium than those of Tazarka (less salt-sensitive) that maintained an unchanged growth. Salt treatment induced oxidative stress in C. tinctorius and the effect was more pronounced in the leaves of the more salt sensitive provenance, Kairouan. Both provenances exhibited a stimulation of antioxidant enzyme activities with higher catalase (CAT) and superoxide dismutase (SOD) activities in Tazarka and higher peroxidase (POD) activity in Kairouan. But, it seems that antioxidant activities were more correlated with polyphenol content. Actually, leaves of Tazarka experienced higher polyphenol and antioxidant activity than Kairouan at 50 mM NaCl. Hence, moderate salinity (3 g NaCl L⁻¹) enhanced bioactive molecule yield in the less salt sensitive provenance, Tazarka. In addition, C. tinctorius was found rich in ascorbic acid, but the moderate salt stress enhanced its production only in the sensitive provenance.     

Effect of NaCl and CaCl<Subscript>2</Subscript> on the antioxidant mechanism of leaves and stems of the rootstock CAB-6P (<Emphasis Type="Italic">Prunus cerasus</Emphasis> L.) under in vitro conditions

The effect of salinity on the non-enzymic and enzymic antioxidant activity, shoot proliferation and nutrient accumulation was studied in in vitro cultures of the rootstock CAB-6P (Prunus cerasus L.). Three concentrations (0, 30 and 60 mM) of NaCl or CaCl₂ were added to a modified MS medium. Between the two salt treatments used, only the explants treated with CaCl₂ presented significant decrease in growth parameters. The concentrations of Na⁺ and Cl⁻ in the explants treated with NaCl were increased, as NaCl in the culture medium increased. Furthermore, in the explants treated with CaCl₂ the concentrations of Ca²⁺ and Cl⁻ were increased while that of K⁺ decreased, as CaCl₂ concentration increased. The activity of peroxidase in leaves as well as the number of its anionic isoforms was increased under 30 mM CaCl₂ as well as 60 mM NaCl or CaCl₂. On the contrary, increasing salinity, from 0 to 60 mM CaCl₂, resulted in a reduction of the catalase activity in leaves followed by disappearance of the only one catalase isoform that was detected in leaves (60 mM CaCl₂). In the stems of the explants treated with NaCl the peroxidase activity was reduced. In the stems and leaves of the explants grown in saline substrate the non-enzymic antioxidant activity was significantly increased. The results suggest that the stems and leaves of CAB-6P explants presented variable antioxidant responses that were depended on the salt form used. The contribution of enzymic and non-enzymic protection mechanisms to the adaptation of CAB-6P explants under salinity stress is discussed.     

Effect of NaCl on fatty acids, phenolics and antioxidant activity of Nigella sativa organs

The objective of this study was to investigate the effect of salinity on growth, fatty acid composition, phenol content and antioxidant activity of Nigella sativa organs. Plants were grown hydroponically under NaCl stress (0, 20 40 and 60 mM). The results indicated that salinity affected N. sativa growth. The fatty acid composition of the leaves and the roots was investigated for the first time and major fatty acids were linolenic acid (58.1%) in the leaves and linoleic (43.9%) and palmitic (33.3%) acids and in the roots. Total fatty acid (TFA) content of the leaves decreased at 60 mM NaCl while root TFA increased at 20 and 40 mM NaCl. Moreover, the fatty acid composition was affected by NaCl; in leaves, the double bond index (DBI) decreased accompanied by a decrease of the level of linolenic acid which reached 14% at 60 mM NaCl. However, root DBI degree increased at 40 at 60 mM NaCl provoked mainly by the increase of the amount of linoleic acid by 15 and 8%, respectively, and the decrease of the amount of palmitic acid by 20 and 14%, respectively. Salt stress increased total polyphenol and individual phenolic acid contents in shoots. Moreover, the antiradical activity of the shoots (DPPH) increased at 60 mM NaCl. However, in roots, the total polyphenol content and the antiradical activity decreased sharply with increasing NaCl doses. Data reported here revealed the variation of fatty acids and phenolic compound contents in different organs of N. sativa, and the possible role of theses changes in the plant salt response were discussed.     

Effects of silicon on photosynthesis,water relations and nutrient uptake of <Emphasis Type="Italic">Phaseolus vulgaris</Emphasis> under NaCl stress

A greenhouse experiment was conducted to investigate the effects of silicon application on Phaseolus vulgaris L. under two levels of salt stress (30 and 60 mM NaCl in the irrigation water). Salinity significantly reduced growth, stomatal conductance and net photosynthetic rate, and increased Na⁺ and Cl⁻ content mainly in roots. Silicon application enhanced growth of salt stressed plants, significantly reduced Na⁺ content especially in leaves and counterbalanced the effects of NaCl on gas exchange; the effect was more evident at 30 mM NaCl. Cl⁻ content in shoots and roots was not significantly modified by silicon application; the drop in K⁺ content caused by salinity was partially counterbalanced by silicon, especially in roots.     

Salicylic acid-mediated changes in photosynthesis,nutrients content and antioxidant metabolism in two mustard (<Emphasis Type="Italic">Brassica juncea</Emphasis> L.) cultivars differing in salt tolerance

Mustard (Brassica juncea L.) cultivars Alankar (salt-tolerant) and PBM16 (salt-sensitive) plants were grown with 50 mM NaCl and were sprayed with 0.1, 0.5, and 1.0 mM salicylic acid (SA) to study the physiological processes determining salt tolerance and to observe the influence of SA application on the alleviation of NaCl-induced adverse effects. The content of leaf Na⁺, Cl⁻, H₂O₂, TBARS, and electrolyte leakage and the activity of SOD were higher in PBM16 than Alankar. In contrast, nutrients content, activity of APX and GR, glutathione content, photosynthetic and growth characteristics were higher in Alankar. Treatment of 50 mM NaCl resulted in increase of Na⁺ and Cl⁻, oxidative stress, activity of antioxidant enzymes and glutathione content, while nutrients content, photosynthetic, and growth characteristics decreased in both the cultivars. Application of 0.5 mM SA alleviated the negative effects of 50 mM NaCl maximally, but 1.0 mM SA proved inhibitory. The effect of SA was more conspicuous in Alankar than PBM16. It is concluded that the higher tolerance of Alankar was due to its lower leaf Na⁺ and Cl⁻ content, higher nutrients content, and efficient antioxidant metabolism. The application of 0.5 mM SA substantially alleviated salt-induced adverse effects in Alankar.     

Plant growth and responses of antioxidants of <Emphasis Type="Italic">Chenopodium album</Emphasis> to long-term NaCl and KCl stress

The effects of long-term NaCl and KCl treatment on plant growth and antioxidative responses were investigated in Chenopodium album, a salt-resistant species widely distributed in semi-arid and light-saline areas of Xinjiang, China. Growth parameters [plant height, branch number, leaf morphology and chlorophyll (Chl) content], the level of oxidative stress [superoxide anion radical (O₂ ⁻), hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) concentrations], activity of antioxidant enzymes [superoxide dismutase (SOD), catalase (CAT), peroxidase (POX)], the contents of non-enzymatic antioxidants [carotenoids (Car) and ascorbic acid (AsA)] and expression of selected genes were investigated. Plants were grown in the presence of 0, 50, and 300 mM NaCl or KCl for 2 months. Growth was stimulated by 50 mM NaCl or KCl, maintained stable at 300 mM NaCl, but was inhibited by 300 mM KCl. Three hundred mM NaCl did not affect O₂ ⁻, H₂O₂, MDA, Car and AsA, but increased the activities of SOD, CAT and POX compared to the controls. RT-PCR analysis suggested that expression of some genes encoding antioxidant enzymes could be induced during long-term salt stress, which was consistent with the enzyme activities. Treatment with 300 mM KCl was associated with elevated oxidative stress, and significantly decreased Car and AsA contents. These results suggest that an efficient antioxidant machinery is important for overcoming oxidative stress induced by treatment with high NaCl concentrations in C. album. Other strategies of ion regulation may also contribute to the differential tolerance to Na and K at higher concentrations.     

Growth,photosynthesis, and ion distribution in hydroponically cultured <Emphasis Type="Italic">Populus alba</Emphasis> L. cuttings grown under various salinity concentrations

Growth, photosynthesis, and Na⁺, K⁺, and Ca²⁺ distributions were investigated in 2-year-old hydroponically cultured Populus alba L. cuttings exposed to salt stresses (0, 0.85, 8.5, 17, and 85 mM NaCl in experiment 1 and 0, 50, 100, 150, and 200 mM in experiment 2) for 4 weeks in 2/5 Hoagland solution. Salt did not markedly inhibit height growth and diameter increment in 150 and 100 mM NaCl, respectively. The 85 mM NaCl treatment increased the dry weights of roots and total dry weight of plants, while 150 mM NaCl significantly reduced the dry weights of leaves, stems, and total plant weight. The decline in the photosynthetic rate lagged 2 weeks behind that of stomatal conductance in the 50 and 100 mM salt solutions. Different ions exhibited different distributions in different parts of the plant. Most Na⁺ ions were excluded and/or compartmentalized in roots at low and moderate salt stress (≤50 mM). K⁺ content in leaves increased with the increase in the salt concentration in the growth solutions.     

Changes in water relations,photosynthetic activity and proline accumulation in one-year-old olive trees (<Emphasis Type="Italic">Olea europaea</Emphasis> L. cv. Chemlali) in response to NaCl salinity

The comparative responses of young olive trees (Olea europaea L. cv “Chemlali”) to different NaCl salinity levels were investigated over 11 months. One-year-old own rooted plants were grown in 10-L pots containing sand and perlite mixture (1:3 v/v). Trees were subjected to three irrigation treatments: CP (control plants that were irrigated with fresh water); SS1 (salt stressed plants irrigated with water containing 100 mM NaCl) and SS2 plants (salt stressed plants irrigated with water containing 200 mM NaCl). Shoot elongation rate, relative water content, leaf water potential and net carbon dioxide exchange rates decreased significantly with increased NaCl salinity level. Under stressed conditions, the increase of Na⁺ and Cl⁻ ions in both leaves and roots was accompanied with that of proline and soluble sugars. The above results show that the accumulation of proline and sugars under stressed conditions could play a role in salt tolerance. The absence of toxicity symptoms under both stress treatments and the superior photosynthetic activity recorded in SS1-treated plants suggest that cv Chemlali is better able to acclimatize to 100 mM NaCl than at 200 mM NaCl. Our findings indicate that saline water containing 100 mM NaCl, the most available water in arid region in Tunisia, can be recommended for the irrigation of cv Chemlali in the arid south of Tunisia.     

Paxillus involutus mycorrhiza attenuate NaCl-stress responses in the salt-sensitive hybrid poplar Populus×canescens

In order to characterise the effect of ectomycorrhiza on Na⁺-responses of the salt-sensitive poplar hybrid Populus × canescens, growth and stress responses of Paxillus involutus (strain MAJ) were tested in liquid cultures in the presence of 20 to 500 mM NaCl, and the effects of mycorrhization on mineral nutrient accumulation and oxidative stress were characterised in mycorrhizal and non-mycorrhizal poplar seedlings exposed to 150 mM NaCl. Paxillus involutus was salt tolerant, showing biomass increases in media containing up to 500 mM NaCl after 4 weeks growth. Mycorrhizal mantle formation on poplar roots was not affected by 150 mM NaCl. Whole plant performance was positively affected by the fungus because total biomass was greater and leaves accumulated less Na⁺ than non-mycorrhizal plants. Energy dispersive X-ray microanalysis using transmission electron microscopy analysis of the influence of mycorrhization on the subcellular localisation of Na⁺ and Cl⁻ in roots showed that the hyphal mantle did not diminish salt accumulation in root cell walls, indicating that mycorrhization did not provide a physical barrier against excess salinity. In the absence of salt stress, mycorrhizal poplar roots contained higher Na⁺ and Cl⁻ concentrations than non-mycorrhizal poplar roots. Paxillus involutus hyphae produced H₂O₂ in the mantle but not in the Hartig net or in pure culture. Salt exposure resulted in H₂O₂ formation in cortical cells of both non-mycorrhizal and mycorrhizal poplar and stimulated peroxidase but not superoxide dismutase activities. This shows that mature ectomycorrhiza was unable to suppress salt-induced oxidative stress. Element analyses suggest that improved performance of mycorrhizal poplar under salt stress may result from diminished xylem loading of Na⁺ and increased supply with K⁺.     

Responses of antioxidant defense system of <Emphasis Type="Italic">Catharanthus roseus</Emphasis> (L.) G. Don. to paclobutrazol treatment under salinity

The effect of paclobutrazol, a plant growth regulator, on antioxidant defense system was investigated in Catharanthus roseus (L.) G. Don. plants subjected to NaCl stress. The growth parameters were significantly reduced under 80 mM NaCl treatment; however, this growth inhibition was less in paclobutrazol-treated (15 mg l⁻¹ plant⁻¹) plants. The non-enzymatic antioxidants ascorbic acid and reduced glutathione were affected under NaCl stress and they increased significantly under paclobutrazol treatment when compared to NaCl treated as well as control plants (P ≤ 0.05). The activity of antioxidant enzyme ascorbate peroxidase showed a significant enhancement under salinity stress. The catalase activity decreased in roots of NaCl-treated plants, but recovered with paclobutrazol treatment. The results suggested that paclobutrazol have significant role in contributing salt stress tolerance of C. roseus by improving the components of antioxidant defense system.     

Biochemical responses of Hyacinth bean (<Emphasis Type="Italic">Lablab purpureus)</Emphasis> to salinity stress

Effect of salinity on Hyacinth bean, Lablab purpureus (HA-4 cultivar) was evaluated in 10-day old seedlings with 100–500 mM NaCl over 72 h of exposure. The stress reduced dry and fresh weight, leaf surface area, root and shoot length, total chlorophyll, and RWC. Oxidative stress markers, H₂O₂, glutathione, TBARS, proline, ascorbic acid, total phenols, and total soluble sugar contents were significantly elevated. Salinity enhanced antioxidant enzymes, POX, and GR activities and reduced that of CAT in concentration and time dependent manner in leaves. Antioxidant enzymes in roots showed inverse relationship with concentration and time of exposure. Metabolic enzyme β-amylase activity increased in both leaves and roots. Acid phosphatase decreased in leaves and elevated in roots. Intensity of constitutive isozymes correlated with in vitro levels under stress, but the protein band patterns differed from controls. Lablab showed reasonable tolerance up to 300 mM NaCl, but leaves and roots differed in their response.     

Photosystem II photochemistry and physiological parameters of three fodder shrubs, <Emphasis Type="Italic">Nitraria retusa</Emphasis>, <Emphasis Type="Italic">Atriplex halimus</Emphasis> and <Emphasis Type="Italic">Medicago arborea</Emphasis> under salt stress

Nitraria retusa and Atriplex halimus (xero-halophytes) plants were grown in the range 0–800 mM NaCl while Medicago arborea (glycophyte) in 0–300 mM NaCl. Salt stress caused a marked decrease in osmotic potential and a significant accumulation of Na⁺ and Cl⁻ in leaves of both species. Moderate salinity had a stimulating effect on growth rate, net CO₂ assimilation, transpiration and stomatal conductance for the xero-halophytic species. At higher salinities, these physiological parameters decreased significantly, and their percentages of reduction were higher in A. halimus than in N. retusa whereas, in M. arborea they decreased linearly with salinity. Nitraria retusa PSII photochemistry and carotenoid content were unaffected by salinity, but a reduction in chlorophyll content was observed at 800 mM NaCl. Similar results were found in A. halimus, but with a decrease in the efficiency of PSII (F′v/F′m) occurred at 800 mM. Conversely, in M. arborea plants we observed a significant reduction in pigment concentrations and chlorophyll fluorescence parameters. The marked toxic effect of Na⁺ and/or Cl⁻ observed in M. arborea indicates that salt damage effect could be attributed to ions’ toxicity, and that the reduction in photosynthesis is most probably due to damages in the photosynthetic apparatus rather than factors affecting stomatal closure. For the two halophyte species, it appears that there is occurrence of co-limitation of photosynthesis by stomatal and non-stomatal factors. Our results suggest that both N. retusa and A. halimus show high tolerance to both high salinity and photoinhibition while M. arborea was considered as a slightly salt tolerant species.     

Accumulation of inorganic and organic osmolytes and their role in osmotic adjustment in NaCl-stressed vetiver grass seedlings

The accumulation of inorganic and organic osmolytes and their role in osmotic adjustment were investigated in roots and leaves of vetiver grass (Vetiveria zizanioides) seedlings stressed with 100, 200, and 300 mM NaCl for 9 days. The results showed that, although the contents of inorganic (K⁺, Na⁺, Ca²⁺, Mg²⁺, Cl⁻, NO₃⁻, SO₄²⁻ and H₂PO₃⁻)) and organic (soluble sugar, organic acids, and free amino acids) osmolytes all increased with NaCl concentration, the contribution of inorganic ions (mainly Na⁺, K⁺, and Cl⁻) to osmotic adjustment was higher (71.50–80.56% of total) than that of organic solutes (19.43–28.50%). The contribution of inorganic ions increased and that of organic solutes decreased in roots with the enhanced NaCl concentration, whereas the case in leaves was opposite. On the other hand, the osmotic adjustment was only effective for vetiver grass seedlings under moderate saline stress (less than 200 mM NaCl).     

Paraquat pre-treatment increases activities of antioxidant enzymes and reduces lipid peroxidation in salt-stressed cucumber leaves

To investigate whether paraquat (PQ) is involved in regulation of antioxidant enzymes and lipid peroxidation under short-term salt stress, and to elucidate the physiological mechanism of salt stress mitigated by PQ, a cucumber cultivar (cv. Chunguang no. 2) was exposed to 100 mM NaCl for 48 h after pre-treatment with 10 μM PQ for 1 h. When compared to the control, salt stress increased the levels of malonaldehyde (MDA), superoxide radical (O₂^·−) and hydrogen peroxide (H₂O₂) and the activities of antioxidant enzymes, such as superoxide dismutase (EC 1.15.1.1), ascorbate peroxidase (EC 1.11.1.11) and glutathione reductase (EC 1.6.4.2) in the cucumber leaves. Under salt conditions, PQ pre-treatment prevented oxidative stress as observed by the decreases in MDA, H₂O₂ and O₂^·− that correlated with the increase in antioxidant defenses. We propose that, at low concentrations, the PQ pre-treatment can reduce the salt-induced oxidative damage by increasing the antioxidative mechanisms in cucumber plants.     

Effect of salt stress on physiological and antioxidative responses in two species of <Emphasis Type="Italic">Salicornia</Emphasis> (<Emphasis Type="Italic">S. persica</Emphasis> and <Emphasis Type="Italic">S. europaea</Emphasis>)

The effects of salt stress on growth parameters, free proline content, ion accumulation, lipid peroxidation, and several antioxidative enzymes activities were investigated in S. persica and S. europaea. The seedlings were grown for 2 months in half-strength Hoagland solution and treated with different concentrations of NaCl (0, 85, 170, 340, and 510 mM) for 21 days. The fresh and dry weights of both species increased significantly at 85 and 170 mM NaCl and decreased at higher concentrations. Salinity increased proline content in both the species as compared to that of control. Sodium (Na⁺) content in roots and shoots increased, whereas K⁺ and P_i content in both organs decreased. At all NaCl concentrations, the total amounts of Na⁺ and K⁺ were higher in shoots than in roots. Malondialdehyde (MDA) content declined at moderate NaCl concentrations (85 and 170 mM) and increased at higher levels. With increased salinity, superoxide dismutase (SOD), catalase (CAT), and guaiacol peroxidase (GPX) activities also increased gradually in both species. In addition, it seems that GPX, CAT, and SOD activities play an essential protective role in the scavenging reactive oxygen species (ROS) in both species. Native polyacrylamide gel electrophoresis (PAGE) indicated different isoform profiles between S. persica and S. europaea concerning antioxidant enzymes. These results showed that S. persica exhibits a better protection mechanism against oxidative damage and it is more salt-tolerant than S. europaea possibly by maintaining and/or increasing growth parameters, ion accumulation, and antioxidant enzyme activities.     

Adventitious root suspension cultures of <Emphasis Type="BoldItalic">Hypericum perforatum</Emphasis>: effect of nitrogen source on production of biomass and secondary metabolites

The present study investigated the effect of nitrogen source (NH₄⁺; NO₃⁻) at different concentrations on the accumulation of biomass and secondary metabolites in adventitious root cultures of Hypericum perforatum L. Cultures were initiated in shake flasks by using half-strength Murashige and Skoog (MS) medium with B5 vitamins, 1.0 mg l⁻¹ indole-3-butyric acid, 0.1 mg l⁻¹ kinetin, 3% (w/v) sucrose, and different ratios of ammonium and nitrate (0:30, 5:25, 10:20, 15:15, 20:10, 25:5, and 30:0 mM, using NH₄Cl and KNO₃). The cultures were maintained in darkness. The medium supplemented with 5:25 (mM) NH₄⁺/NO₃⁻ resulted in the optimum accumulation of biomass and total phenols and flavonoids. The antioxidant potential of a methanolic extract, measured as the 1, 1-diphenyl-2-picrylhydrazyl and 2, 2-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) radical scavenging activities, of H. perforatum adventitious roots showed that antioxidant activity was high from root extracts that were grown on higher concentrations of NO₃⁻ nitrogen (15, 20, and 25 mM). Further, assessment of hydrogen peroxide (H₂O₂) and malondialdehyde content of the root extracts revealed that cultures supplemented with higher levels of NO₃⁻ nitrogen (15–30 mM) were under oxidative stress, which boosted the levels of secondary metabolites in the adventitious roots. These results suggest that optimal adventitious root biomass could be achieved with the supplementation of cultures with 5:25 ratios of MS nitrogen sources.     

Effects of NaCl or Na<Subscript>2</Subscript>SO<Subscript>4</Subscript> salinity on plant growth,ion content and photosynthetic activity in <Emphasis Type="Italic">Ocimum basilicum</Emphasis> L.

Basil (Ocimum basilicum L., cultivar Genovese) plants were grown in Hoagland solution with or without 50 mM NaCl or 25 mM Na₂SO₄. After 15 days of treatment, Na₂SO₄ slowed growth of plants as indicated by root, stem and leaf dry weight, root length, shoot height and leaf area, and the effects were major of those induced by NaCl. Photosynthetic response was decreased more by chloride salinity than by sulphate. No effects in both treatments on leaf chlorophyll content, maximal efficiency of PSII photochemistry (F _v/F _m) and electron transport rate (ETR) were recorded. Therefore, an excess of energy following the limitation to CO₂ photoassimilation and a down regulation of PSII photochemistry was monitored under NaCl, which displays mechanisms that play a role in avoiding PSII photodamage able to dissipate this excess energy. Ionic composition (Na⁺, K⁺, Ca²⁺, and Mg²⁺) was affected to the same extent under both types of salinity, thus together with an increase in leaves Cl⁻, and roots SO₄ ²⁻ in NaCl and Na₂SO₄-treated plants, respectively, may have resulted in the observed growth retardation (for Na₂SO₄ treatment) and photosynthesis activity inhibition (for NaCl treatment), suggesting that those effects seem to have been due to the anionic component of the salts.     

Osmotic adjustment,water relations and growth attributes of the xero-halophyte <Emphasis Type="Italic">Reaumuria vermiculata</Emphasis> L. (Tamaricaceae) in response to salt stress

Reaumuria vermiculata (L.), a perennial dwarf shrub in the family of Tamaricaceae, is a salt-secreting xero-halophyte found widely in arid areas of Tunisia. In the present study, physiological attributes of R. vermiculata were investigated under salt stress. Four-month-old plants were subjected to various salinity levels (0, 100, 200, 300, 400 or 600 mM NaCl) for 30 days under greenhouse conditions. Results showed that plants grew optimally when treated with standard nutrient solution without NaCl supply. However, increasing osmolality of nutrient solutions caused a significant reduction in biomass production and relative growth rate. This reduction was more pronounced in roots than in shoots. In addition, this species was able to maintain its shoot water content at 30% of the control even when subjected to the highest salt level, whereas root water content seemed to be unaffected by salt. Shoot water potential declined significantly as osmotic potential of watering solutions was lowered and the more negative values were reached at 600 mM NaCl (−3.4 MPa). Concentrations of Na⁺ and Cl⁻ in the shoots of R. vermiculata were markedly increased with increasing osmolality of nutrient solutions, whereas concentration of K⁺ was not affected by NaCl supply. Salt excretion is an efficient mechanism of Na⁺ exclusion from the shoots of this species exhibiting high K⁺/Na⁺ selectivity ratio over a wide range of NaCl salinity. Proline accumulation in shoots was significantly increased with increase in salt level and may play a role in osmoregulation.     

Antioxidant Enzyme Activities in Arbuscular Mycorrhizal (<Emphasis Type="Italic">Glomus intraradices</Emphasis>) Fungus Inoculated and Non-inoculated Maize Plants Under Zinc Deficiency

A greenhouse experiment was conducted to examine the changes in antioxidant enzyme activities of arbuscular mycorrhizal (AM) fungus Glomus intraradices Schenck and Smith inoculated (M+) and non-inoculated (M−) maize (Zea mays L.) plants (variety COHM5) under varying levels of zinc (0, 1.25, 2.5, 3.75 and 5.0 mg kg⁻¹). Roots and shoots sampled at 45 days after sowing (DAS) were estimated for its antioxidant enzymes (superoxide dismutase, peroxidase) IAA oxidase, polyphenol oxidase, acid phosphatase and nutritional status especially P and Zn concentrations. Mycorrhizal inoculation significantly (P ≤ 0.01) increased all the four antioxidant enzymes in both roots and shoots at 45 DAS regardless of Zn levels. All enzyme activities except SOD increased progressively with increasing levels of Zn under M+ and M− conditions. The SOD activity got decreased in roots and shoots at 2.5 and 3.75 mg Zn kg⁻¹. Acid phosphatase activity in M+ roots and shoots were higher in all levels of Zn but the values decreased with increasing levels of Zn particularly in roots. Mycorrhizal fungus inoculated plants had higher P and Zn concentrations in both stages in comparison to non-inoculated plants. Our overall data suggest that mycorrhizal symbiosis plays a vital role in enhancing activities of antioxidant enzymes and nutritional status that enables the host plant to sustain zinc deficient conditions.