Quantitative and Qualitative Changes in Peroxidase during Germination of Mung Bean under Salt Stress

Seeds of mung bean (Phaseolus aureus Roxb.) cv. Pusa Baisakhi were surface sterilized with sodium hypochlorite solution and sown both in Petri dishes and in sand culture containing aqueous solutions of four different salts, viz. NaCI, KCI, Na₂SO₄ and K₂SO₄, each at 5 and 10 S/cm. Peroxidase activity and its isoenzymes were studied in different plant parts at suitable time intervals during germination. Activity of peroxidase increased in embryo axis and leaves but decreased in cotyledons and roots with different salt treatments to varying degrees. A highly significant inverse correlation (r= -0.931 was found between the peroxidase level and the growth of embryo axis under saline conditions. The number of isoenzymes of peroxidase increased with increase in the time of germination. Salinity treatments resulted in the appearance of new isoenzymes in all the plant organs except roots where the isoenzymic pattern remained unchanged. Different types of salinity resulted in the appearance or/and disappearance of different isoenzymes.     

Cowpea ribonuclease: properties and effect of NaCl-salinity on its activation during seed germination and seedling establishment

Pitiúba cowpea [Vigna unguiculata (L.) Walp] seeds were germinated in distilled water (control treatment) or in 100 mM NaCl solution (salt treatment), and RNase was purified from different parts of the seedlings. Seedling growth was reduced by the NaCl treatment. RNase activity was low in cotyledons of quiescent seeds, but the enzyme was activated during germination and seedling establishment. Salinity reduced cotyledon RNase activity, and this effect appeared to be due to a delay in its activation. The RNases from roots, stems, and leaves were immunologically identical to that found in cotyledons. Partially purified RNase fractions from the different parts of the seedling showed some activity with DNA as substrate. However, this DNA hydrolyzing activity was much lower than that of RNA hydrolyzing activity. The DNA hydrolyzing activity was strongly inhibited by Cu²⁺, Hg²⁺, and Zn²⁺ ions, stimulated by MgCl₂, and slowly inhibited by EDTA. This activity from the most purified fraction was inhibited by increasing concentrations of RNA in the reaction medium. It is suggested that the major biological role of this cotyledon RNase would be to hydrolyze seed storage RNA during germination and seedling establishment, and it was discussed that it might have a protective role against abiotic stress during later part of seedling establishment.     

Effect of iso-osmotic levels of salts and PEG-6000 on enzymes in germinating pea seeds

Effects of iso-osmotic levels of salts (NaCl, CaCl₂, Na₂SO₄) and PEG-6000 on the activity of hydrolytic and nitrogen assimilatory enzymes in pea embryo axis and coty ledon were studied. The activity of nitrate reductase and nitrite reductase in embryo axis and cotyledon and the activity of protease and α-amylase in cotyledon decreased with decreasing medium osmotic potential as compared to control at all the stages of seedling growth. The activity of protease and amylase increases with increasing levels of stress in embryo axis. Sodium chloride induced, stress had more deleterious effects on the activity of nitrate reductase, nitrite reductase and αamylase followed by other salts and PEG-6000. On the other hand, CaCl₂ induced salt stress was more depressive for protease activity. The maximum increase in the activity of protease and amylase was observed in embryo axis at higher concentration of salts and PEG-6000.     

Vigna Radiata Seed Germination under Salinity

Salinity reduced mung bean (Vigna radiata Wilczek) radicle and root elongation, delayed and inhibited hypocotyl elongation and mobilization of reserves from the cotyledons to the embryo axis. Fresh and dry masses and water content of the embryo axes were reduced. Under salinity, a net leakage of K to the media increased with time and increasing NaCl concentrations. Sugars present in the cotyledons of seeds were of primary importance for growth of the embryo axis upto 18 h after sowing whereas breakdown of starch by amylase contributed later, the contribution being delayed and reduced with increasing NaCl concentration. Even when amylase activity in the cotyledons was progressively reduced with increasing NaCl concentration, the increasing contents of soluble sugars in the cotyledons indicated that sugars were not limiting for mung bean seedling growth under salinity.     

Changes in isoenzymes of soluble malate dehydrogenase during germination of mung bean (Phaseolus aureus Roxb.) under salt stress

Seeds of mung bean (Phaseolus aureus Roxb.) cv. Pusa Baisakhi were surface sterilized and sown both in Petri dishes and sand culture containing aqueous solutions of four different saltsviz. NaCl, KC1, Na₂SO₄ and K₂SO₄ each at 5 and 10 m ?^-1 cm^-1. Malate dehydrogenase (MDH) isoenzymes were studied in different plant parts of mung bean at suitable intervals during germination under four different salts. In cotyledons, 96 h after sowing only one isoenzyme was left in control as compared to three under salt treatment. In the embryo axis, 96 h after sowing, sulphate salts resulted in the disappearance of isoenzymes with R₁ 0.43 and 0.62, whereas isoenzyme with R₁ 0.62 was missing only at a higher concentration of chloride salts. Chloride salts also resulted in the disappearance of band with R₁ 0.15, both in the embryo axis and leaves. However, in the roots the isoenzymic pattern remains the same with all the salt treatments.     

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.     

披针叶黄华试管苗适应盐胁迫的渗透调节机制

以披针叶黄华(Thermopsis lanceolata)试管苗为材料,通过组培方法研究其在0、0.2%、0.4%、0.6%、0.8%和1.0%NaCl和Na2SO4胁迫30d后的生长、有机渗透调节物质和无机渗透调节物质(Na+、K+和Ca2+)含量的变化,以探讨其耐盐性机制。结果显示:(1)随NaCl和Na2SO4胁迫浓度的增加,披针叶黄华试管苗叶片脯氨酸和可溶性糖含量均显著持续增加,且NaCl胁迫下脯氨酸上升的幅度均大于相同浓度Na2SO4胁迫下的增幅,而可溶性糖上升的幅度却小于相同浓度Na2SO4胁迫下的幅度;可溶性蛋白含量随NaCl浓度的增大呈先升高后降低的趋势,但随Na2SO4浓度的增加呈持续上升的趋势。(2)随NaCl和Na2SO4浓度的增加,披针叶黄华试管苗Na+含量呈增加趋势且各处理均显著高于对照,Ca2+含量和叶片K+含量却呈逐渐减少趋势且各处理均显著低于对照,而根系K+含量呈先降后升的趋势;Na2SO4胁迫下披针叶黄华试管苗叶片Na+含量上升幅度以及K+和Ca2+含量下降幅度均明显低于相同浓度NaCl胁迫组;而Na+/K+和Na+/Ca2+比值随NaCl和Na2SO4浓度增加而升高;NaCl胁迫下,叶片Na+/K+和Na+/Ca2+高于相同浓度Na2SO4胁迫下的比值,而根系Na+/K+和Na+/Ca2+却低于相同浓度Na2SO4胁迫下的比值。研究表明,盐胁迫下,披针叶黄华试管苗通过抑制叶片中Na+积累并增加可溶性糖和可溶性蛋白含量,在根系中维持较高K+和Ca2+含量以及较低水平Na+/K+和Na+/Ca2+比,以降低披针叶黄华细胞渗透势来适应盐渍环境;披针叶黄华对NaCl胁迫的调节能力弱于Na2SO4。     

Combination Effect of NaCl Salinity and Nitrogen Form on Mineral Composition of Sunflower Plants

The effect of two N-forms (NH₄ ⁺ and NO₃ ^–) and NaCl on pattern of accumulation of some essential inorganic nutrients was examined in sunflower (Helianthus annuus L.) cv. Hisun 33. Eight-day-old plants of were subjected for 21 d to Hoagland's nutrient solution containing 8 mM N as NH₄ ⁺ or NO₃ ^·, and salinized with and addition of NaCl to the growth medium had no significant effect on total leaf N. However, root N of NH₄-supplied plants decreased significantly with increase in NaCl concentration, whereas that of NO₃-supplied plants remained unaffected. There was no significant effect of NaCl on leaf or root P, but the NO₃-supplied plants had significa concentration of leaf P than that of NH₄-supplied plants at varying salt treatments. Salinity of the rooting med did not show any significant effect on Na⁺ concentrations of leaves or roots of plants subjected to two differen N. NH₄-treated plants generally had greater concentrations of Cl^– in leaves and roots and lower K⁺ content in leaves than NO₃-supplied plants. Ca²⁺ concentrations of leaves and roots and Mg²⁺ concentrations of leaves decreased in NH₄-supplied plants due to NaCl, but they remained unaffected in NO₃-treated plants.     

Light and ethylenediamine tetraacetic acid mediated differential effects of ammonium on nitrate reductase activity in maize seedlings

Abstract Effect of ammonium on in vivo activity of nitrate reductase in roots, shoots and leaves of maize (Zea mays L.) seedlings was studied in relation to light/dark conditions and EDTA supply. Supply of 5 mM (NH₄)₂SO₄ increased the steady state level of enzyme only in leaves and in light, while it had no effect in roots and shoots and in the dark. The substrate induction of enzyme was also little affected by 1 to 10 mM (NH₄)₂SO₄ in roots and shoots. In the leaves the activity in the dark was either inhibited (minus EDTA) or stimulated (plus EDTA) by 5 to 10 mM (NH₄)₂SO₄. The activity was stimulated in the light also in the presence of EDTA at higher concentrations of ammonium. When different concentrations of ammonium were supplied without any exogenous nitrate in the light, the enzyme activity increased at low concentration and was either inhibited or unaffected at higher concentrations depending upon the tissue used. Supply of EDTA with ammonium modified its effect to some extent. It is suggested that the effect of ammonium on nitrate reductase activity depends upon the tissue used and the effective concentration of the ammonium.     

Changes in the levels of jasmonates and free polyamines induced by Na<Subscript>2</Subscript>SO<Subscript>4</Subscript> and NaCl in roots and leaves of the halophyte <Emphasis Type="Italic">Prosopis strombulifera</Emphasis>

Prosopis strombulifera, a common legume in high-salinity soils of Argentina, is a useful model for elucidation of salt tolerance mechanisms and specific biochemical pathways in halophytes, since its NaCl tolerance exceeds the limit described for most halophytic plants. We analyzed the effects of the increasing concentration of two main soil salts, Na₂SO₄ and NaCl, on growth parameters of P. strombulifera, chlorophyll levels, and content of jasmonates (JAs) and polyamines (PAs), which are key molecules involved in stress responses. P. strombulifera showed a halophytic response (growth promotion) to NaCl, but strong growth inhibition by iso-osmotic solutions of Na₂SO₄. Chlorophyll levels, number of leaves and leaf area were also differentially affected. An important finding was the partial alleviation of SO₄²⁻ toxicity by treatment with two-salt mixture. JAs are not directly involved in salt tolerance in this species since its levels decrease under all salt treatments. Beneficial effects of Putrescine (Put) accumulation in NaCl treated plants maybe inferred probably associated with the antioxidative defense system. Another novel finding is the accumulation of the uncommon PA cadaverine in roots under high Na₂SO₄, which may be related to SO₄²⁻ toxicity.     

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.     

The Effects of Sucrose and Light on the Level of Soluble and Particle-bound Ribonuclease Activities in Excised Avena Leaves

Incubation of excised Avena leaves in a wet chamber in darkness resulted in an increase in both soluble and particle-bound Rnase activities. Illumination promoted the increase in the total RNase which occurred upon leaf excision. The light-induced increase in total RNase was due to an increase in soluble RNase. The increase in RNase activity in the particulate fraction was inhibited by illumination. Feeding 2 per cent sucrose to the tissues in the dark increased the level of soluble RNase and decreased the activity found in the particulate fraction. Treatment of the illuminated tissues with 10^?4M dichlorophenyldimethylurea (DCMU) inhibited the effects of light on the RNase level. It is concluded that the light-effect is explained at least in part by the photosynthetic production of sugars. In excised leaves kept in darkness the RNA content rapidly decreased. Feeding sugars to or illumination of the tissues lowered the rate of RNA breakdown due to leaf excision. DCMU counteracted the light effect. In general, the decrease of RNA was repressed by all treatments leading to an inhibition of the increase of particulate RNase. On the other hand, the observed changes of the soluble RNase were not related with the variations of RNA. Treatment with 3 M urea increased the RNase activity both in the particulate and the soluble fractions. The RNase activity of soluble preparations, partially purified on a Sephadex G-50 column or by (NH₄)₂SO₄ fractionation, was also stimulated by 3 M urea. Treatment with 10^?5M kinetin repressed the increase in RNase activity due to leaf excision both in the soluble and the particulate fractions.     

Effects of NaCl, Na2SO4, and mannitol on storage lipid mobilization in the cotyledons and roots of purple alfalfa seedlings

The effects of NaCl, Na₂SO₄, and mannitol on mobilization of storage lipids in the cotyledon mesophyll and root meristem cells during the germination of purple alfalfa (Medicago sativa L.) seeds were studied using the transmission electron microscopy technique. The ultrastructural analysis showed that the number and shape of specific organelles, oleosomes, depended on the osmotic effects of a salt used. In control seedlings grown on distilled water, lipid mobilization in roots terminated by the 4th day, and in cotyledons, only by the 8th day. The disruptions in the storage lipid mobilization in the treated seedlings were specific and depended on the stress agent used, the osmotic pressure induced by this agent, as well as on the tissue type. The presence of a great number of oleosomes in the cytoplasm of cells subjected to osmotic stress, in contrast to the control ones, demonstrated the inhibition of mobilization processes. All concentrations of Na₂SO₄ and mannitol suppressed lipid mobilization in the cotyledons and roots. At the same time, NaCl markedly suppressed this process in the root cells only at a higher osmotic pressure of the solution. The results obtained suggest that the cytological analysis of cotyledon storage-lipid mobilization can tentatively assess the resistance of dicotyledonous plants to abiotic stresses.     

Organ-specific changes in the content of free and conjugated polyamines in <Emphasis Type="Italic">Mesembryanthemum crystallinum</Emphasis> plants under salinity

The content of free and conjugated polyamines (PA) was studied in the leaves of secondary shoots and in roots of the facultative halophyte Mesembryanthemum crystallinum L. under salinity. Plants were grown in water culture and at the age of 10 weeks were subjected to salinity stress by a single introduction of NaCl into nutrient medium to a final concentration of 400 mM. In 0, 6, 24, and 48 h, the content of free, HClO₄-soluble, and HClO₄-insoluble conjugates of PA were measured in leaves and roots. The levels of free and conjugated PA in the roots of control plants and plants subjected to salinity stress were higher than in the leaves. In response to salinity shock, the content of all forms of spermine (Spm), particularly its HClO₄-soluble conjugates, increased in roots and leaves. In contrast, the content of Spm precursors, putrescine (Put) and spermidine (Spd), as well as their HClO₄-soluble conjugates, decreased. Salinity treatment elevated the content of free cadaverine both in roots and leaves, whereas the content of its conjugated forms decreased, which might suggest transition of conjugated forms of cadaverine into the free form. The product of oxidative degradation of Spm and Spd, 1,3-diaminopropane (Dap), was absent in leaves, whereas the content of free and conjugated forms of this diamine in roots increased under salinity conditions. The obtained data indicate organ specificity for the content of free and conjugated forms of PA, as well as their active role in adaptation of Mesembryanthemum crystallinum to salinity shock.     

Enzyme activities in germinating Mungbean (Phaseolus aureus) seeds and their relation with promoter and inhibitors of protein synthesis

Summary Assay of the hydrolyzing enzyme levels, viz.-amylase, adenosine triphosphatase (ATPase), phytase and ribonuclease (RNase) in the germinating Mungbean (Phaseolus aureus) seeds is made to evaluate the degree of substrate breakdown at different periods of germination. In addition to the cotyledons, the principal site of hydrolases, an evidence of their occurrence in the growing embryo has been presented. Enzyme activities in storage tissues, i. e. cotyledons and growing embryo, i. e. axis rise to a maximum sometime between initial and final phase of germination and then declined.Effects of gibberellic acid, chloramphenicol, actinomycin D, and 5-fluorouracil on such enzymes in cotyledons have also been studied to assess how enzyme synthesis is affected by exogenous GA₃ and protein synthesis inhibitors. While GA₃ is able to promote enzyme activities, particularly,-amylase and RNase, protein synthesis inhibitors remarkably inhibited them indicating net enzyme synthesis during germination.     

Effect of some nitrogenous salts on nitrogen transfer and protease activity in germinatingZea mays L. seeds

Maize seeds were allowed to germinate in the presence of different nitrogenous salts for 72 h. Changes in the ethanol soluble and insoluble nitrogen were studied in the embryo and in the endosperm. Supply of Ca(NC₃)₂ enhanced germination and protease activity in the endosperm resulting in greater solubilisation of protein to soluble nitrogen in the seeds. NH₄NO₃ and (NH₄)₂SO₄ were less effective as compared to Ca(NO₃)₂. Cycloheximide inhibited germination and protease activity. Pretreatment also resulted in increase in growth, soluble and insoluble nitrogen, and nitrate reductase activity in the primary leaves. Ca(NO₃)₂ was more effective than NH₄NO₃ and (NH₄)₂SO₄.     

Leaf gas exchange,water relations,nutrient content and growth in citrus and olive seedlings under salinity

The effects of salinity on growth, leaf nutrient content, water relations, gas exchange parameters and chlorophyll fluorescence were studied in six-month-old seedlings of citrus (Citrus limonia Osbeck) and rooted cuttings of olive (Olea europaea L. cv. Arbequina). Citrus and olive were grown in a greenhouse and watered with half strength Hoagland’s solution plus 0 or 50 mM NaCl for citrus, or plus 0 or 100 mM NaCl for olive. Salinity increased Cl⁻ and Na⁺ content in leaves and roots in both species and reduced total plant dry mass, net photosynthetic rate and stomatal conductance. Decreased growth and gas exchange was apparently due to a toxic effect of Cl⁻ and/or Na⁺ and not due to osmotic stress since both species were able to osmotically adjust to maintain pressure potential higher than in non-salinized leaves. Internal CO₂ concentration in the mesophyll was not reduced in either species. Salinity decreased leaf chlorophyll a content only in citrus.     

Salt tolerance potential of wild resources of the tribe Triticeae

The salt tolerance potential of variousAegilops species of different genome combinationsviz., Aegilops squarrosa, Ae. cylindrica, Ae. ovata. Ae. triuncialis, Ae. variabilis, Ae. bicornis, Ae. longissima, Ae. umbellulata, andAe. sharonensis was tested to identify the high salt-tolerant genotype(s). Screening was done in cement tanks filled with gravel and Hoagland nutrient solution. Salinity was created by mixing Na₂SO₄, CaCl₂, MgCl₂ and NaCl in the ratio of 10∶5∶1∶4 and induced by a stepwise increase in electrical conductivity number of tillers and number of leaves. Inter-and intragenomic variations for cation uptake were also significant. Species with DD and CD genome were found to be highly tolerant. Possible factors responsible for these observations have been discussed.     

In vitro regeneration of Sophora toromiro from seedling explants

Embryonic axes with cotyledons, shoot-tips of embryonic axes, isolated cotyledons, as well as axillary buds and leaves from 20-year-old trees of Sophora toromiro, were evaluated for their capacity to trigger organogenesis and to regenerate plantlets under in vitro conditions. Embryonic shoot-tips were the only explants capable of regenerating plants. They developed rapidly in vitro in the presence of NAA and BA while in subculture roots were induced at the proximal end in the presence of 0.49 μM IBA within 40–60 days. Development was completed with a subculture phase under non-sterile conditions using a mixture of equal parts of sterilized vermiculite/sand/soil in growth chambers, before final acclimation in the greenhouse. In the presence of NAA, BA and GA₃, whole embryonic axes formed multiple shoots that branched when grown in 2.27 or 11.35 μM TDZ in subculture. Similarly, callus was initiated at the embryo axis base, developing into several new shoots in the presence of TDZ. Because of the relatively high shoot induction rate along the embryonic axis, this axis presents a valuable source of new juvenile explants. Growth and rhizogenesis was satisfactory only when organs from seed pods of the year or from the previous season were used. Experiments with isolated cotyledons produced callus only, while axillary buds and leaves did not show any responses in the presence of several growth regulators assayed. Inoculation of seedlings with various strains of rhizobia under in vitro conditions resulted in root outgrowths, but not in nodules that are typical of rhizobia infection. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effects of NaCl and Na2SO4 on red-osier dogwood (Cornus stolonifera Michx) seedlings

Sodium chloride and sodium sulfate are commonly present in extraction tailings waters produced as a result of surface mining and affect plants on reclaimed areas. Red-osier dogwood (Cornus stolonifera Michx) seedlings were demonstrated to be relatively resistant to these high salinity oil sands tailings waters. The objectives of this study were to compare the effects of Na₂SO₄ and NaCl, on growth, tissue ion content, water relations and gas exchange in red-osier dogwood (Cornus stolonifera Michx) seedlings. In the present study, red-osier dogwood seedlings were grown in aerated half-strength modified Hoagland's mineral solution containing 0, 25, 50 or 100 mM of NaCl or Na₂SO₄. After four weeks of treatment, plant dry weights decreased and the amount of Na⁺ in plant tissues increased with increasing salt concentration. Na⁺ tissue content was higher in plants treated with NaCl than Na₂SO₄ and it was greater in roots than shoots. However, Cl^– concentration in the NaCl treated plants was higher in shoots than in roots. The decrease in stomatal conductance and photosynthetic rates observed in presence of salts is likely to contribute to the growth reduction. Our results suggest that red-osier dogwood is able to control the transport of Na⁺ from roots to shoots when external concentrations are 50 mM or less.