The impact of heavy metals on the activity of some enzymes along the barley root

Barley seedlings 48 h after the onset of germination on filter paper treated for 24 h by 1 mM cadmium (Cd), 3 mM nickel (Ni) or 0.5 mM mercury (Hg) showed similar approximately 45% root growth inhibition. Although root growth inhibition was similar, loss of cell viability evaluated, as Evans blue uptake was distinct among Cd, Ni and Hg treated roots. While Cd and Hg caused cell death along the whole barley root (0–8 mm), Ni induced significant loss of cell viability only in root cells 6–8 mm distance from the root tip. Our results suggest that different metabolic processes are activated in different parts of barley root in relation to distance from the root tip during heavy metal (HM) treatment. Some of them are characteristic for several HMs such as inhibition of ascorbic acid oxidase or glutathione-S-transferase stimulation, while others are specific for individual HMs, e.g. activation of acid phosphatase and lipoxygenase by Cd and Hg, or inhibition of ascorbate peroxidase by Ni and Hg treatment.     

Effect of long-term salinity on cellular antioxidants,compatible solute and fatty acid profile of Sweet Annie (Artemisia annua L.)

Impact of long-term salinity and subsequent oxidative stress was studied on cellular antioxidants, proline accumulation and lipid profile of Artemisia annua L. (Sweet Annie or Qinghao) which yields artemisinin (Qinghaosu), effective against cerebral malaria-causing strains of Plasmodium falciparum. Under salinity (0.0–160 mM NaCl), in A. annua, proline accumulation, contents of ascorbate and glutathione and activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), glutathione reductase (GR) and catalase (CAT) increased, but the contents of reduced forms of glutathione (GSH) and ascorbate declined. The fatty-acid profiling revealed a major salinity-induced shift towards long-chain and mono-saturated fatty acids. Myristic acid (14:0), palmitoleic acid (16:1), linoleic acid (18:2) and erucic acid (22:1) increased by 141%, 186%, 34% and 908%, respectively, in comparison with the control. Contents of oleic acid (18:1), linolenic acid (18:3), arachidonic acid (22:0) and lignoceric acid (24:0) decreased by 50%, 17%, 44% and 78%, respectively. Thus, in A. annua, salinity declines ascorbate and GSH contents. However, increased levels of proline and total glutathione (GSH + GSSG), and activities of antioxidant enzymes might provide a certain level of tolerance. Modification in fatty-acid composition might be a membrane adaptation to long-term salinity and oxidative stress.     

Alleviating the adverse effects of NaCl stress in maize seedlings by pretreating seeds with salicylic acid and 24-epibrassinolide

The effects of bio-regulators salicylic acid (SA) and 24-epibrassinolide (EBL) as seed soaking treatment on the growth traits, content of photosynthetic pigments, proline, relative water content (RWC), electrolyte leakage percent (EC%), antioxidative enzymes and leaf anatomy of Zea mays L. seedlings grown under 60 or 120 mM NaCl saline stress were studied. A greenhouse experiment was performed in a completely randomized design with nine treatments [control (treated with tap water); 60 mM NaCl; 120 mM NaCl; 10^− 4 M SA; 60 mM NaCl + 10^− 4 M SA; 120 mM NaCl + 10^− 4 M SA; 10 μM EBL; 60 mM NaCl + 10 μMEBL or 120 mM NaCl + 10 μM EBL] each with four replicates. The results indicated that NaCl stress significantly reduced plant growth traits, leaf photosynthetic pigment, soluble sugars, RWC%, and activities of catalase (CAT), peroxidase (POX) as well as leaf anatomy. However, the application of SA or EBL mitigated the toxic effects of NaCl stress on maize seedlings and considerably improved growth traits, photosynthetic pigments, proline, RWC%, CAT and POX enzyme activities as well as leaf anatomy. This study highlights the potential ameliorative effects of SA or EBL in mitigating the phytotoxicity of NaCl stress in seeds and growing seedlings.     

Modulation of antioxidant enzyme activities and metabolites ratios by nitric oxide in short-term salt stressed soybean root nodules

Several abiotic factors cause molecular damage to plants either directly or through the accumulation of reactive oxygen species such as hydrogen peroxide (H₂O₂). We investigated if application of nitric oxide (NO) donor 2,2′-(hydroxynitrosohydrazono) bis-ethanimine (DETA/NO) could reduce the toxic effect resulting from short-term salt stress. Salt treatment (150 mM NaCl) alone and in combination with 10 μM DETA/NO or 10 μM DETA were given to matured soybean root nodules for 24 h. Salt stress resulted in high H₂O₂ level and lipid peroxidation while application of DETA/NO effectively reduced H₂O₂ level and prevented lipid peroxidation in the soybean root nodules. NO treatment increased the activities of ascorbate peroxidase and dehydroascorbate reductase under salt stress. Whereas short-term salt stress reduced AsA/DHAsA and GSH/GSSG ratios, application of the NO donor resulted in an increase of the reduced form of the antioxidant metabolites thus increasing the AsA/DHAsA and GSH/GSSG ratios. Our data suggests a protective role of NO against salt stress.     

Simultaneous application of salicylic acid and calcium improves salt tolerance in two contrasting tomato (Solanum lycopersicum) cultivars

Soil salinity is one of the most important environmental factors responsible for serious agricultural problems. Tomato salt tolerance may be improved by genetic selection and by the use of adapted physiological tools. The aim of this study was to investigate the impact of exogenous application of salicylic acid (SA 0.01 mM) and calcium sulphate (CaSO₄ 5 mM), singly or in combination, on plant growth, photosynthetic pigments, nutritional behaviour and some metabolic parameters (total chlorophyll, carotenoids, soluble sugars, proline and lipid peroxidation) of two tomato cultivars (cv. Super Marmande and cv. Red River) exposed to salt stress (100 mM NaCl). Application of 100 mM NaCl reduced plant growth, total chlorophyll and carotenoid contents. Salt stress also induced an accumulation of Na⁺, a decrease in K⁺ and Ca^2 + concentration and root sugar level, an increase in malondialdehyde (MDA) and proline concentration. Deleterious impact of salinity was related to modification in ion content rather than modification in the plant water status. Exogenous application of SA or Ca alone improved plant behaviour in the presence of NaCl. Nevertheless, the best results in terms of growth, photosynthetic pigment concentrations and mineral nutrition (limitation of Na⁺ accumulation and maintenance of K⁺ and Ca^2 + content) were obtained in response to the combined SA + Ca treatment. Although the involved physiological parameters varied depending on the considered cultivar, our results suggest that Ca^2 + and SA may interact to reduce the stress experienced by the plant in the presence of NaCl.     

Effect of nodules on dehydration response in alfalfa (Medicago sativa L.)

Drought is a key abiotic stress that negatively affects growth and development as well as symbiotic nitrogen fixation in alfalfa (Medicago sativa L.). To understand whether nodulation would affect drought stress response in alfalfa, we analyzed the lipid peroxidation, activities of antioxidant enzymes including superoxide dismutase (SOD), and catalase (CAT), contents of superoxide anion radical, non-enzymatic antioxidants including reduced glutathione (GSH) and proline, total protein, and soluble sugar in dehydration-stressed alfalfa. Three-month-old alfalfa plants without nodule, with active nodules, or with inactive nodules were dehydrated for 0, 1, 2, 4, 6, 8, and 10 h. We found that roots and leaves from plants with nodules, especially with active nodules, showed less lipid peroxidation which was associated with higher CAT activities and higher levels of GSH. Roots and leaves with active nodules also accumulated less free proline and soluble sugar compared to plants without nodules, suggesting that proline and soluble sugar may have a limited role in osmotic adjustment in these plants. The results suggested that active nodules may have a positive effect on drought stress tolerance in alfalfa.     

Comparative lipid peroxidation,antioxidant defense systems and proline content in roots of two rice cultivars differing in salt tolerance

The changes in the activity of antioxidant enzymes such as superoxide dismutase (SOD: EC 1.15.1.1), catalase (CAT: EC 1.11.1.6), peroxidase (POX: EC 1.11.1.7), ascorbate peroxidase (APOX: EC 1.11.1.11) and glutathione reductase (GR: EC 1.6.4.2), free proline content, and the rate of lipid peroxidation level in terms of malondialdehyde (MDA) in roots of two rice cultivars (cvs.) differing in salt tolerance were investigated. Plants were subjected to three salt treatments, 0, 60, and 120 mol m⁻³ NaCl for 7 days. The results showed that activated oxygen species may play a role in cellular toxicity of NaCl and indicated differences in activation of antioxidant defense systems between the two cvs. The roots of both cultivars showed a decrease in GR activity with increase in salinity. CAT and APOX activities increased with increasing salt stress in roots of salt-tolerant cultivar Pokkali but decreased and showed no change, respectively, in roots of IR-28 cultivar. POX activity decreased with increasing NaCl concentrations in salt-tolerant Pokkali but increased in IR-28. SOD activity showed no change in roots of both cultivars under increasing salinity. MDA level in the roots increased under salt stress in sensitive IR-28 but showed no change in Pokkali. IR-28 produced higher amount of proline under salt stress than in Pokkali. Increasing NaCl concentration caused a reduction in root fresh weight of Pokkali and root dry weight of IR-28. The results indicate that improved tolerance to salt stress in root tissues of rice plants may be accomplished by increased capacity of antioxidative system.     

Thiol-peptide level and proteomic changes in response to cadmium toxicity in Oryza sativa L. roots

In the present study, rice seedlings were exposed to a range of Cd concentrations (0.1 μM, 1 μM, 10 μM, 100 μM and 1 mM) for 15 days and a combination of different molecular approaches were used to evidence Cd effects and to assess the plants’ ability to counteract metal toxicity. At a macroscopical level, only the highest Cd concentration (1 mM) caused a complete plant growth inhibition, whereas the lowest concentrations seemed to stimulate growth. At genome level, the amplified fragment length polymorphism (AFLP) technique was applied to detect DNA sequence changes in root cells, showing that all the Cd concentrations induced significant DNA polymorphisms in a dose-dependent manner. Data also evidenced the absence of preferential mutation sites.Plant responses were analysed by measuring the levels of gluthatione (GSH) and phytochelatins (PCs), the thiol-peptides involved in heavy metal tolerance mechanisms. Results showed a progressive increase of GSH up to 10 μM of Cd treatment, whereas a significant induction only of PC₃ was detected in roots of plants exposed to 100 μM of Cd. As suggested by the proteome analysis of root tissues, this last concentration strongly induced the expression of regulatory proteins and some metabolic enzymes. Furthermore, the treatment with 10 μM of Cd induced changes in metabolic enzymes, but it mainly activated defence mechanisms by the induction of transporters and proteins involved in the degradation of oxidatively modified proteins.     

Water status and water diffusion transport in lupine roots exposed to lead

Water status and diffusion transport were studied in the roots of yellow lupine (Lupinus luteus L., cv. Juno) treated for 48 h with two selected concentrations of Pb(NO₃)₂: 150 mg l⁻¹, which inhibited root growth by about 50% (medium stress intensity), as well as 350 mg l⁻¹, which almost entirely suppressed root elongation (severe stress intensity). Relative water content (RWC), which characterizes the degree of root water saturation, slightly increased at the lower lead concentration and remained unchanged at the higher lead dose. Ultrastructure analyses under a transmission electron microscope revealed that plasmolysis was not evoked by lead in the apical part of the meristem. Moreover, direct observation of meristem cells using Nomarsky optics indicated enhanced vacuolization in the presence of both lead concentrations. These data suggest that the water status of the roots was not affected by the metal. Due to the fact that proline is involved in the maintenance of turgor in the cells, the metabolism of this amino acid was investigated. In the roots, the activity of enzymes involved in proline synthesis, such as pyrroline-5-carboxylate synthetase (P5CS) and ornithine aminotransferase (OAT), increased at 150 mg l⁻¹ Pb²⁺; nevertheless, proline content was diminished at the lower lead concentration. This effect is likely the result of proline degradation by proline dehydrogenase (PDH), since the activity of this enzyme increased at the lower lead dose. On the other hand, in the presence of 350 mg l⁻¹ Pb²⁺, a low level of proline was correlated with a decrease in the activity of P5CS and OAT, as well as unchanged PDH activity in lupine roots. These data may imply that enzymatic synthesis of proline was strongly damaged by the metal ions. The low level of proline in both experimental variants suggests that proline accumulation is inessential to maintaining the osmotic uptake of water into root cells. NMR spectroscopy showed that exposition of lupine seedlings to lead caused a deceleration in water transport in the roots due to a reduction in the water transfer rate across the membranes (transmembrane transfer) and vacuoles continuum, as well as water diffusion along the root apoplast. Fluorescence staining and immunogold labeling showed the presence of callose strands in cell walls and/or in the vicinity of them. In lead-treated lupine roots, callose was mainly localized in the parenchyma cortex placed lengthwise to the vascular cylinder. Callose deposits in the cell walls may reduce vacuolar transport, as well as increase cell wall resistance to water flow. Deceleration of diffusional water movement to the vascular system, may in turn, influence the rate of long-distance water transport to aerial parts of the plant.     

Metabolic adaptations to mercury-induced oxidative stress in roots of Medicago sativa L

Alfalfa (Medicago sativa) roots were treated with mercuric ions in a concentration- and time-dependent manner, and lipid peroxidation was studied biochemically as well as histochemically along with other physiological responses. Histochemical staining with Schiff's reagent and Evans blue revealed that the peroxidation of membrane lipids and loss of plasma membrane integrity in Hg-treated roots occurred in the meristem and the elongation zone. The histochemical observations were supported by the quantitative determinations of thiobarbituric acid reactive substances (TBARS). However, under the mercuric ions stress, the alfalfa plants showed no significant alteration of hydrogen peroxide in roots. Analysis of lipoxygenase activity by non-denaturing polyacrylamide gel electrophoresis (PAGE) showed that there were two isoforms in the root of alfalfa plants, but they showed quite different patterns under the Hg exposure. Also, using non-denaturing PAGE, activities of superoxide dismutase (SOD) and peroxidase (POD) were determined in roots after treatment with Hg ions. The total activities of SOD and POD increased in roots after Hg treatment of roots. Activity of ascorbate peroxides (APX) was stimulated at relatively high concentration of Hg (40microM), and after prolonged Hg exposure (20microM, 24h). In contrast, glutathione reductase activity was depressed at higher concentrations of Hg (10-20microM). Treatments of seedlings with 10-40microM Hg decreased the ascorbate and glutathione amounts but increased total non-protein thiols. The above results indicated that Hg exerted its toxic effect on the root growth of alfalfa by induction of oxidative stress.     

Antioxidant activity and expression of catalase gene of (Eustoma grandiflorum L) in response to boron and aluminum

Aluminum (Al) is the most inhibiting factor for plant root elongation in acidic soils. Boron (B) is an essential micronutrient whose deficiency occurs in acid soils because of high leaching. Lisianthus (Eustoma grandiflorum L.) is a plant to which Al seems to be beneficial, but the range of B requirement for its growth is not documented yet. Both Al toxicity and B deficiency result in oxidative stress in certain plants. The present study was aimed to evaluate the effects of B and Al on the activity of antioxidant system of rooted cuttings of lisianthus. The plants were grown in nutrient solution and treated with 0, 0.05 and 0.1 mM of boron and 0.88 mM of aluminum for 24 h. Activity of certain antioxidant enzymes and the contents of non-enzymatic antioxidants were evaluated. The expression of CAT gene was quantified by semi-quantitative RT-PCR technique. Increase activities of superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) and increase of flavonoids and anthocyanin contents was observed in the plants which treated with 0.1 mM B and 0.88 mM Al, compared to those treated with 0 and 0.05 mM B. Increase of CAT activity was the most pronounced among antioxidant enzymes and was parallel with increased expression of its gene. The results showed that Al and B (in higher concentration) provide lisianthus plant with reinforced antioxidant system.     

Effect of mercury and gold on growth,nutrient uptake,and anatomical changes in Chilopsis linearis

Plants of Chilopsis linearis were grown with 0, 50, 100, and 200 μM Hg [as Hg(CH₃COO)₂] and 0 and 50 μM Au (as KAuCl₄) in hydroponics. The results showed that seedling grown with 50 μM Au + 50 μM Hg and 50 μM Au + 100 μM Hg had roots 25 and 55% shorter than control roots, respectively. The element uptake determination using ICP/OES demonstrated that Hg at 50 and 100 μM (with and without Au) significantly increased (p < 0.05) the S concentration in leaves. On the other hand, the concentration of Fe significantly increased in roots of plants treated with Au–Hg. In addition, the stems of plants treated with Hg at 100 μM, with and without Au, had 239 and 876 mg Hg/kg dry biomass (d wt), respectively. Also, at 50 μM Hg, with and without Au, stems accumulated 375 and 475 mg Hg/kg d wt. The Hg concentration in leaves (287 mg Hg/kg d wt) was higher (p < 0.05) for the treatment containing 50 μM Au + 100 μM Hg. Without Au, the Hg concentration in leaves decreased to 75 mg Hg/kg d wt. Toxicity symptoms induced by Hg in cortex cells and the vascular system were lower in plants exposed to 50 μM Au + 50 μM Hg compared to plants exposed to 50 μM Hg only. Further, the SEM micrographs revealed deposition of Au–Hg particles inside the root. Although the concentrations of Hg used in this study showed different degree of toxicity, the plants displayed good agronomic value.     

Short and long-term uptake of Hg in white lupin plants:Kinetics and stress indicators

The intrinsic characteristics of white lupin regarding biomass production and tolerance to abiotic stresses could make it a good candidate to be used in degraded mine soils containing mercury (Hg), but white lupin behaviour in response to Hg has to be previously evaluated. With this aim, kinetic parameters of Hg uptake in short and long-term experiments, and Hg resistance of white lupin plants using several stress indicators were studied. The plants were grown with increasing Hg doses in nutrient solutions (0, 5 and 10 μM). Hg uptake showed an active component in Hg influx, suggesting the existence of a low affinity root transporter that can be used for Hg uptake into white lupin root cells. K_m and V_max values obtained for the saturable component were 217.7 ± 27.6 μM and 3.78 ± 0.18 μmol Hg g FW^?1 h^?1. Hg accumulation was concentration–time-dependent, showing a saturable behaviour for the lower doses but a linear behaviour for the highest ones. A high ability of Hg absorption by white lupin was observed both in short and long-term uptake experiments. The highest Hg dose reduced biomass production especially in the shoots. Moreover, increases in chlorophylls, malondialdehyde, total thiols and phenols were observed in Hg-stressed plants. The enhancement of total thiols and phenols levels in roots reduced oxidative stress for the 5 μM dose, but not for higher Hg levels. The deleterious effect of Hg was less marked in root tissues, in spite of their accumulation of very high Hg amounts (99%) because of, at least in part, a combined increase in total thiols and phenolics able to minimize oxidative stress. Our results suggested that phenolic content in roots could be used as a new and easy-to-use indicator of Hg presence. On the whole, white lupin showed a certain ability to survive in Hg-contaminated media and it would be possible to include it in combined decontamination strategies.     

Salicylic acid changes morpho-physiological attributes of feverfew (Tanacetum parthenium L.) under salinity stress

Feverfew (Tanacetum parthenium) (TP) is a valuable medicinal plant from Asteraceae family with various pharmaceutical and therapeutic properties. A pot experiment was conducted to evaluate the effect of salicylic acid (SA) on the physiological and morphological responses of TP under salinity stress. Salinity was induced by NaCl and CaCl₂ (2:1) at 30, 60, 90, 120, 150 and 180 mM levels. SA was applied as foliar application at 0, 200 and 300 ppm concentrations. Plant height, leaf and shoot number, fresh and dry weight and essential oil, starch, sugar, protein, proline, catalase (CAT), peroxidase (POD), and ascorbic peroxidase (APX) contents were as measured morpho-physiological traits. The results showed that SA significantly (P ≤ 0.05) improved the measured traits and caused higher tolerance in TP plants under salinity stress. The essential oil content increased with increasing the salinity level up to 90 mM, which was more significant when combined with SA application. All of the measured traits except proline content, antioxidant enzymes, essential oil and sugar decreased at high salinity levels.     

Biochemical indicators of salt stress in Plantago maritima: Implications for environmental stress assessment

Our study is focused on native spontaneous species of saline ecosystems Plantago maritima. Plants were cultivated at several salt concentrations (0, 50, 100, 200, 300, 400 and 500 mM NaCl) in a glass greenhouse under semi-controlled conditions. Growth parameters, water parameters and ionic status were determined and they were used as criteria to assess the response of P. maritima under a salinity gradient. Catalase, guaiacaol and ascobate peroxidase activities, total protein and proline were also determined. Our results show that P. maritima is a facultative halophyte capable of expressing its maximum growth potential at relatively low concentrations of salt (less than 3 g l⁻¹ NaCl). At high doses of salt (concentrations > 200 mM), the decrease in the growth of P. maritima is associated to a decrease in the uptake of K⁺. There is a disruption of the water intake of their organs and therefore results an invasion of the cytoplasm by Na⁺ toxic ion. However, stressed plants use K⁺ more sparingly. They invest especially in the production of biomass expressed by the dry weight of the shoots, and they use Na⁺ and proline for osmotic adjustment. The halophyte studied is able to accumulate high levels of proline in response to increasing salt concentration. The accumulation of the amino compound, mainly in roots, is interpreted as an indicator of salt tolerance. Additionally, a significant correlation between the tolerance of the plants to salinity and the activity of several antioxidant enzymes has been observed. Hence, we suggest the possibility of using these activities as a biochemical indicator for salt tolerance in P. maritima. Our study points out two types of biomarkers of salt exposure: enzymatic biomarkers in the leaves and proline content in the roots. Both did show very good correlation with salt exposure, and thus may be considered good biomarkers of exposure with a very good dose–response relationship.     

Brassica napus subjected to copper excess: Phospholipases C and D and glutathione system in signalling

Brassica napus plants were subjected to an oxidative stress by incubating them with 100 μM CuSO₄ for different times. The early response to copper stress was evaluated studying changes at both root and leaf level in the putative lipid and antioxidative signals diacylglicerol (DAG), phosphatidic acid (PA) and glutathione, in order to achieve elucidation on how these two kind of signals are related to each other. Activation of phospholipases C (PLC) and D (PLD) was studied in roots and leaves whereas increases in the levels of total and reduced glutathione (GSH) and changes in its redox status were evaluated in roots, leaves and chloroplast stroma. PLC and PLD were measured by studying the production of DAG, PA and phosphatidylbutanol (PtdButOH). PA, PtdButOH as well as DAG increased in roots already after 1 min of the treatment whereas in leaves, where no translocation of the metal occurred, any increase in PA and DAG was observed and no PtdButOH was formed. Roots were affected by oxidative stress showing decreases in glutathione reductase (GR), in total glutathione (GSH + GSSG) and GSH, and increases in oxidised glutathione (GSSG). In leaves, GR was induced during the whole stress period and both GSH + GSSG and GSH showed a peak at 5 min of the treatment. In the stroma, the maximum presence in GSH + GSSG and GSH occurred with a time shift of 25 min compared with total leaf extract.     

Glutathione-supplemented tris-citric acid extender improves the post-thaw quality and in vivo fertility of buffalo (Bubalus bubalis) bull spermatozoa

In this study we evaluated the effects of semen extender supplementation with different concentrations of glutathione (GSH) on buffalo (Bubalus bubalis) bull sperm motility, plasma membrane integrity, viability and DNA integrity as well as in vivo fertility. Semen from three Nili-Ravi buffalo bulls was collected, and qualified semen ejaculates (n = 18) were split into five aliquots for dilution (37 °C; 50 × 10⁶ spermatozoa ml^?1) with experimental tris-citric acid extender containing 0, 0.5, 1.0, 1.5 or 2.0 mM GSH. Extended semen was cooled to 4 °C, equilibrated and filled in French straws. The straws were kept on liquid nitrogen vapors (5 cm above the LN₂ level) for 10 min and plunged in liquid nitrogen for storage. Sperm motility (%), plasma membrane integrity (%), viability (%) and DNA integrity (%) were assessed at 0, 2 and 4 h post-thawing (37 °C). Extender supplementation with GSH (0.5, 1.0, 1.5 and 2.0 mM) increased sperm motility, plasma membrane integrity and viability in a dose dependent manner. Sperm DNA integrity was higher (p < 0.05) in all experimental extenders containing GSH when compared to the control extender (0 mM GSH). The in vivo fertility rate of cryopreserved buffalo bull (n = 2) spermatozoa was higher (p < 0.05) in extender containing 2.0 mM GSH compared to that of control. In summary, tris-citric acid extender supplemented with glutathione improved the freezability of buffalo bull spermatozoa in a dose dependant manner. Moreover, the addition of 2.0 mM GSH to the extender enhanced the in vivo fertility of buffalo (Bubalus bubalis) bull spermatozoa.     

Avocado roots treated with salicylic acid produce phenol-2,4-bis (1,1-dimethylethyl), a compound with antifungal activity

We demonstrated the ability of salicylic acid (SA) to induce a compound in avocado roots that strengthens their defense against Phytophthora cinnamomi. The SA content of avocado roots, before and after the application of exogenous SA, was determined by High-Performance Liquid Chromatography (HPLC). After 4 h of SA feeding, the endogenous level in the roots increased to 223 μg g⁻¹ FW, which was 15 times the amount found in control roots. The methanolic extract obtained from SA-treated avocado roots inhibited the radial growth of P. cinnamomi. A thin layer chromatographic bioassay with the methanolic extract and spores of Aspergillus showed a distinct inhibition zone. The compound responsible for the inhibition was identified as phenol-2,4-bis (1,1-dimethylethyl) by gas chromatography and mass spectrometry. At a concentration of 100 μg/mL, the substance reduced germinative tube length in Aspergillus and radial growth of P. cinnamomi. A commercial preparation of phenol-2,4-bis (1,1-dimethylethyl) caused the same effects on mycelium morphology and radial growth as our isolate, confirming the presence of this compound in the root extracts. This is the first report of the induction of this compound in plants by SA, and the results suggest that it plays an important role in the defense response of avocado.     

The combined effects of gibberellic acid and salinity on some antioxidant enzyme activities,plant growth parameters and nutritional status in maize plants

The combined effects of salt stress and gibberellic acid (GA₃) on plant growth and nutritional status of maize (Zea mays L. cv., DK 647 F1) were studied in a pot experiment. Treatments were (1) control (C): nutrient solution alone, (2) salt stress (S): 100 mM NaCl, (3) S + GA1: 100 mM NaCl and 50 ppm GA₃ and (4) S + GA2: 100 mM NaCl and 100 ppm GA₃. Salt stress (S) was found to reduce the total dry matter, chlorophyll content, relative water content (RWC), but to increase proline accumulation, superoxide dismutase (SOD; EC 1.15.1.1), peroxidase (POD; EC 1.11.1.7) and polyphenol oxidase (PPO; 1.10.3.1) enzyme activities and electrolyte leakage. GA₃ treatments overcame to variable extents the adverse effects of NaCl stress on the above physiological parameters. GA₃ treatments reduced the activities of enzyme in the salt-stressed plants. Salt stress reduced some macro and micronutrient concentrations but exogenous application of GA₃ increased these to levels of control treatment. Foliar application of GA₃ counteracted some of the adverse effects of NaCl salinity with the accumulation of proline which maintained membrane permeability and increased macro and micronutrient levels.     

Soybean root growth inhibition and lignification induced by p-coumaric acid

The effects of 0.25–2 mM p-coumaric acid, a phenylpropanoid metabolite with recognized allelopathic properties, were tested on root growth, cell viability, phenylalanine ammonia-lyase (PAL) activities, soluble and cell wall-bound peroxidase (POD) activities, hydrogen peroxide (H₂O₂) level and lignin content and its monomeric composition in soybean (Glycine max (L.) Merr.) roots. At ≥0.25 mM, exogenously supplied p-coumaric acid induced premature cessation of root growth, increased POD activity and lignin content and decreased the H₂O₂ content. At ≥0.5 mM, the allelochemical decreased the cell viability and PAL activity. When applied jointly with PIP (an inhibitor of the cinnamate 4-hydroxylase, C4H), 1 mM p-coumaric acid increased lignin content. In contrast, the application of MDCA (an inhibitor of the 4-coumarate:CoA ligase, 4CL) with p-coumaric acid did not increase lignin content. The lignin monomeric composition of p-coumaric acid-exposed roots revealed a significant increase of p-hydroxyphenyl (H) and guaiacyl (G) units. Taken together, these results suggest that p-coumaric acid's mode of action is entry via the phenylpropanoid pathway, resulting in an increase of H and G lignin monomers that solidify the cell wall and restrict soybean root growth.