Response of Pteris vittata to different cadmium treatments

Pteris vittata is known as an arsenic hyperaccumulator, but there is little information about its tolerance to cadmium and on its ability to accumulate this heavy metal. Our aim was to analyse the accumulation capacity, oxidative stress and antioxidant response of this fern after cadmium treatments. Cadmium content, main markers of oxidative stress and antioxidant response were detected in leaves of plants grown in hydroponics for both short- (5 days) and long- (15 days) term exposure to 0 (control) 60 and 100 μM CdCl₂. In leaves, the concentration of cadmium and oxidative stress were parallel with the increase of cadmium exposure. In the short-term exposure, antioxidant response was sufficient to contrast cadmium phytotoxicity only in 60 μM cadmium-treated plants. In the long-term exposure all treated plants, in spite of the increase in activity of some peroxide-scavenging enzymes, showed a significant increase in oxidative damage. As in the long-term stress markers were comparable in all treated plants, with no clear correlation with hydrogen peroxide content, at least part of cadmium-induced oxidative injury seems not mediated by H₂O₂. Based on our studies, P. vittata, able to uptake relatively high concentrations of cadmium, is only partially tolerant to this heavy metal.     

Antioxidant system activation by mercury in Pfaffia glomerata plantlets

Oxidative stress caused by mercury (Hg) was investigated in Pfaffia glomerata plantlets grown in nutrient solution using sand as substrate. Thirty-day-old acclimated plants were treated for 9 days with four Hg levels (0, 1, 25 and 50 μM) in the substrate. Parameters such as growth, tissue Hg concentration, toxicity indicators (δ-aminolevulinic acid dehidratase, δ-ALA-D, activity), oxidative damage markers (TBARS, lipid peroxidation, and H₂O₂ concentration) and enzymatic (superoxide dismutase, SOD, catalase, CAT, and ascorbate peroxidase, APX) and non-enzymatic (non-protein thiols, NPSH, ascorbic acid, AsA, and proline concentration) antioxidants were investigated. Tissue Hg concentration increased with Hg levels. Root and shoot fresh weight and δ-ALA-D activity were significantly decreased at 50 μM Hg, and chlorophyll and carotenoid concentration were not affected. Shoot H₂O₂ concentration increased curvilinearly with Hg levels, whereas lipid peroxidation increased at 25 and 50 μM Hg, respectively, in roots and shoots. SOD activity showed a straight correlation with H₂O₂ concentration, whereas CAT activity increased only in shoots at 1 and 50 μM Hg. Shoot APX activity was either decreased at 1 μM Hg or increased at 50 μM Hg. Conversely, root APX activity was only increased at 1 μM Hg. In general, AsA, NPSH and proline concentrations increased upon addition of Hg, with the exception of proline in roots, which decreased. These changes in enzymatic and non-enzymatic antioxidants had a significant protective effect on P. glomerata plantlets under mild Hg-stressed conditions.     

Phosphatase and phytase activities in nodules of common bean genotypes at different levels of phosphorus supply

Plants grown at limited P supply can increase the activity of phosphatases in roots to hydrolyse organic-P compounds in the soil thus improving plant P acquisition, but little information is available about the role of these enzymes for internal plant metabolism at limited-P conditions. This work intended to measure the activities of acid phosphatases and phytases in nodules of common bean (Phaseolus vulgaris) genotypes at different levels of P supply. The experiment was carried out in a 5?×?5 factorial design with four replicates, comprising five bean genotypes and five P levels (20, 40, 80, 160 and 320 μmol P plant^?1 week^?1) in nutrient solution. Root seedlings were inoculated with Rhizobium tropici and plants were grown in 1-l bottles. Nodule samples were detached from 39-day-old plants and enzyme activities were determined in crude extracts. Plants were harvested at the stage of pod setting. Polynomial models fitted to data indicated maximal values at the level of 194 μmol P for shoot mass, at 206 μmol P for nodule mass and at 221 μmol P for shoot N. Whereas shoot mass was 1.7 times lower at 20 than at 160 μmol P, nodule mass was 7.5 times lower. Concentration of P in nodules increased from 40 to 320 μmol P but remained stable between 20 and 40 μmol P, suggesting a minimal threshold concentration of 3 mg P g^?1 for nodule growth. Activities of phosphatases and phytases in nodules decreased strongly as P supply was raised from 20 to 80 μmol P, remaining almost stable at higher P levels. Phosphatase activity ranged from 1,154 to 406 nmol min^?1 g^?1 (nodule fresh mass) from 20 to 80 μmol P respectively, while the phytase activity ranged from 55 to 14 nmol min^?1 g^?1 from 20 to 80 μmol P. Bean genotypes differed in shoot and nodule mass at the levels of 80 and 160 μmol P, whilst they differed in nodule enzyme activities only at the lowest P level, the relationship between nodule enzyme activities and growth of different bean genotypes was not evident. It is concluded that bean plants at P-deficient conditions increase the activities of phosphatases and phytases in nodules. This may constitute an adaptive mechanism for N₂-fixing legumes to tolerate P deficiency, by increasing the utilisation of the scarce P within the nodules.     

Involvement of heme oxygenase as antioxidant defense in soybean nodules

Objective: We have previously demonstrated that the inducible form of heme oxygenase plays a critical role in protecting against oxidative stress in mammals. To gain further insight into the functions of this enzyme in plants, we have tested its activity and expression in soybean nodules subjected to cadmium (Cd) stress.

Materials and methods: Four-weeks-old soybean nodulated plants were treated with different cadmium chloride concentrations (0, 50 and 200 μM) during 48 h. Oxidative stress parameters such as TBARS content, GSH levels and antioxidant enzyme activities were measured as well as heme oxygenase activity and expression. Besides, the effect of biliverdin and Zn-protophorphyrin IX were analized.

Results: Treatment with 200 μM Cd during 48 h caused a 67% increase in TBARS content, whereas GSH decreased 44%, and total superoxide dismutase, gluthatione reductase and guaiacol peroxidase were also inhibited 54, 20 and 60%, respectively. A total of 200 μM Cd produced the overexpression of heme oxygenase-1, as well as a 10-fold enhancement of its activity. Co-administration of biliverdin (10 μM) completely prevented the effects caused by Cd. Treatment with Zn protoporphyrin IX, a strong inhibitor of heme oxygenase, expectedly decreased heme oxygenase-1 activity to half. When the inhibitor was given together with Cd, completely prevented the enzyme induction and oxidative stress parameters were significantly enhanced.

Conclusion: Taking together, these results are indicating that heme oxygenase plays a protective role against oxidative cell damage in soybean nodules.     

Oxidative stress occurs during soybean nodule senescence

Several markers of oxidative stress were measured in 2- to 10-week-old soybean (Glycine max [L.] Merr.) nodules. There were increases in peroxides, protein carbonyls and modified DNA base concentrations with nodule age. The catalytic iron content also increased significantly during nodule ageing. Iron contained in the peribacteroid space was effective in promoting lipid peroxidation and this might contribute to the degradation of the peribacteroid membrane in senescing nodules. The concentration of the oxidized forms of glutathione and homoglutathione increased significantly during nodule development and the concentration of reduced glutathione and homoglutathione decreased during senescence. Taken together, these results are consistent with the development of oxidative stress in senescing nodules. Significant DNA and protein damage also occurred in the first days of nodule development, suggesting that an earlier period of oxidative stress might occur in the period over which the symbiosis becomes established. Received: 7 July 1998 / Accepted: 30 November 1998     

Glaucocalyxin A and B Regulate Growth and Induce Oxidative Stress in Lettuce (Lactuca sativa L.) Roots

Glaucocalyxin (Gla) A–C are major ent-kaurane diterpenoids isolated from Isodon japonicus var. glaucocalyx (Maxim.) H. W. Li. This study investigated the possible interference of these diterpenoids with root growth and its mechanism of action in lettuce (Lactuca sativa L.) seedlings. Results indicated the dual stimulatory and inhibitory effects of Gla A and B on root growth and their phytotoxic effects on root hair development. The promotion of root growth by lower levels of Gla A and B (20–40 μM) resulted from enhanced cell length and increased mitotic activity. However, higher concentrations (80–200 μM) of Gla A and B had inhibitory effects. In addition, Gla A and B inhibited root hair development of lettuce seedlings in a dose-dependent manner at concentrations between 20 and 200 μM. Exposure of lettuce roots to Gla A and B at 200 μM increased levels of malondialdehyde and the generation of O ₂ ^·? , indicating lipid peroxidation and induction of oxidative stress. Activities of the antioxidant enzymes superoxide dismutase, catalase, and peroxidase were significantly elevated. Reactive oxygen species (ROS) scavengers dihydroxybenzene disulfonic acid (Tiron) and dimethylthiourea at 100 μM could efficiently alleviate the phytotoxicity induced by Gla A and B at 200 μM. These results demonstrated that the deleterious effect of Gla A and B at higher concentrations (80–200 μM) on roots may occur through the imposition of oxidative stress on cell growth and cell division. Due to the lack of an α,β-unsaturated ketone in α-methylenecyclopentanone moiety, Gla C could not induce ROS generation and exhibited no effect on the roots, even at the highest concentration (200 μM). Therefore, the α-methylenecyclopentanone moiety in the ent-kaurene diterpenoids was presented as an essential possible active center for the phytotoxicity.     

In vitro biochemical evaluation of cadmium tolerance mechanism in callus and seedlings of Brassica juncea

In vitro grown callus and seedlings of Brassica juncea were treated with equimolar concentrations of cadmium and compared for their respective tolerance to cadmium. Calli cultures were grown on Murashige and Skoog medium supplemented with α 6-benzyl aminopurine (200 µg L^?1, naphthalene acetic acid 200 µg L^?1) and 2,4-dichloro-phenoxy acetic acid (65 µg L^?1) while the seedlings grown on Hoagland's nutrient solution have been carried out. Cellular homeostasis and detoxification to cadmium in B. juncea were studied by analyzing the growth in terms of fresh weight and dry weight, lipid peroxidation, proline accumulation, and antioxidative enzymes (superoxide dismutase (SOD), ascorbate peroxidase (APX), and catalase (CAT)). At 200 µM cadmium, callus and seedlings showed 73.61% and 74.76% reduction in tolerance, respectively. A significant increase in malondialdehyde (MDA) content was found in both calli and seedlings; however, the amount of MDA content was more in seedlings. Proline content increased on lower concentration of cadmium (up to 50 µM), and it further decreased (up to 200 µM). But the accumulation of proline was higher in callus cultures. The overall activity of antioxidative enzymes (SOD, CAT, and APX) was found to be higher in callus in comparison to seedlings of B. juncea. Callus and seedlings showed a significant (P?≤?0.5) increase in SOD activity in a concentration-dependent manner up to 50 µM cadmium concentration but decreased further. APX activity increased significantly at low cadmium levels but CAT activity decreased significantly throughout on increasing cadmium concentrations from 5 to 200 µM, respectively. Hence, it was observed that callus of B. juncea was more tolerant in comparison to seedlings exposed to equimolar concentrations of cadmium. Thus, from the present studies, it is concluded that calli were more tolerant toward cadmium-induced oxidative stress. Hence, it is suitable material for the study of cadmium tolerance mechanisms and for the manipulations within them for better understanding of cadmium detoxification strategies in B. juncea.     

Aluminium Stress Affects Nitrogen Fixation and Assimilation in Soybean (Glycine max L.)

Nitrogen fixation and assimilation in nodules and roots were studied in soybean (Glycine max L.) exposed to different levels of aluminium (Al) stress (0, 50, 200 and 500 μM). Al at 500 μM induced oxidative stress, which became evident from an increase in lipid peroxidation accompanied by a concomitant decline in antioxidant enzyme activities and leghaemoglobin breakdown. Consequently, there was also a reduction in nitrogenase activity. However, the leghaemoglobin levels and nitrogenase activity were unexpectedly found to be higher in nodules when the plants were treated with 200 μM Al. Of the enzymes involved in nitrogen assimilation, the activity of glutamate dehydrogenase-NADH was reduced in nodules under Al stress, but it was significantly higher in roots at 500 μM Al as compared to that in the control. In nodules, the glutamine synthetase/glutamate synthase-NADH pathway, assayed in terms of activity and expression of both the enzymes, was inhibited at >50 μM Al; but in roots this inhibitory effect was apparent only at 500 μM Al. No significant changes in ammonium and protein contents were recorded in the nodules or roots when the plants were treated with 50 μM Al. However, Al at ≥200 μM significantly increased the ammonium levels and decreased the protein content in the nodules. But these contrasting effects on ammonium and protein contents due to Al stress were observed in the roots only at 500 μM Al. The results suggest that the effect of Al stress on nitrogen assimilation is more conspicuous in nodules than that in the roots of soybean plants.     

Neuroprotective Effects of Theaflavins Against Oxidative Stress-Induced Apoptosis in PC12 Cells

Oxidative stress can induce neuronal apoptosis via the production of superoxide and hydroxyl radicals. This process is as a major pathogenic mechanism in neurodegenerative disorders. In this study, we aimed to clarify whether theaflavins protect PC12 cells from oxidative stress damage induced by H₂O₂. A cell model of PC12 cells undergoing oxidative stress was created by exposing cells to 200 μM H₂O₂ in the presence or absence of varying concentrations of theaflavins (5, 10, and 20 μM). Cell viability was monitored using the MTT assay and Hoechst 33258 staining, showing that 10 μM theaflavins enhanced cell survival following 200 μM H₂O₂ induced toxicity and increased cell viability by approximately 40?%. Additionally, we measured levels of intracellular reactive oxygen species (ROS) and antioxidant enzyme activity. This suggested that the neuroprotective effect of theaflavins against oxidative stress in PC12 cells is derived from suppression of oxidant enzyme activity. Furthermore, Western blot analyses indicated that theaflavins downregulated the ratio of pro-apoptosis/anti-apoptosis proteins Bax/Bcl-2. Theaflavins also downregulated the expression of caspase-3 compared with a H₂O₂-treated group that had not been treated with theaflavins. Interestingly, this is the first study to report that the four main components of theaflavins found in black tea can protect neural cells (PC12) from apoptosis induced by H₂O₂. These findings provide the foundations for a new field of using theaflavins or its source, black tea, in the treatment of neurodegenerative diseases caused by oxidative stress.     

Nodule Structure and Functioning in Chickpea (Cicer Arietinum) as Affected by Salt Stress

Cicer arietinum L. plants raised in sand culture under natural light were subjected to salinity stress induced by mixture of NaCl, CaCl₂, MgCl₂ and MgSO₄ (40, 60 or 80 meq dm^-3). Acetylene reduction activity (ARA) of nodules, leghemoglobin content and nodule structure were followed 55, 75 and 85 d after sowing. ARA declined significantly under salt treatments and the lowest ARA was observed at day 85 after sowing. Decrease in ARA was consistent with decreased nodule leghemoglobin content. The leghemoglobin content of control plants decreased by 50 % at day 85 indicating senescence of nodules. This senescence was further accelerated by salt treatment after which the leghemoglobin content fell to negligible levels. The structural changes associated with salt stress were mainly reduction in size of the nodules, decreased meristematic zone, reduced number and degradation of symbiosomes, reduced intercellalar spaces and deposition of electron dense material in the intercellular spaces in the cortex of nodules.     

Protective Effect of Selenomethionine on Aflatoxin B1-Induced Oxidative Stress in MDCK Cells

AFB1 is a mycotoxin which exerts their cytotoxicity through increasing oxidative damage in target organ. Kidney is one of target organs vulnerable to damage caused by AFB1. In this study, Madin-Darby canine kidney (MDCK) cells were used to evaluate the AFB1-induced cell damage by the MTT assay. The results revealed that the toxic effect of AFB1 on MDCK cells is both dose and time dependent. Half maximal toxic concentration (IC₅₀) was noted at 0.25 μg/ml of AFB1. Further, protective effect of six different concentrations (0.2, 0.8, 1, 2, 4, and 8 μM) of selenomethionine (SeMet) was observed against 0.25 μg/ml of AFB1-induced damage. The results showed that 0.25 μg/ml of AFB1 caused significant increase in oxidative stress, which was demonstrated by significant increase of malondialdehyde (MDA) level, reduction of intracellular GSH level, as well as GPX1 activity and mRNA level in MDCK cells when compared with control. SeMet protected the cells from AFB1-induced oxidative damage in a dose-dependant manner. Good protection could be achieved between 1 and 4 μM of concentration. Amid this range, MDA level significantly decreased while intracellular GSH level and GPX1 activity in addition to mRNA level significantly increased. Moreover, cell viability was significantly improved. It could be concluded that SeMet is a potential antioxidative agent to alleviate AFB1-induced oxidative stress.     

Cadmium Alters the Concentration of Fatty Acids in THP-1 Macrophages

Fatty acid composition of human immune cells influences their function. The aim of this study was to evaluate the effects of known toxicant and immunomodulator, cadmium, at low concentrations on levels of selected fatty acids (FAs) in THP-1 macrophages. The differentiation of THP-1 monocytes into macrophages was achieved by administration of phorbol myristate acetate. Macrophages were incubated with various cadmium chloride (CdCl₂) solutions for 48 h at final concentrations of 5 nM, 20 nM, 200 nM, and 2 μM CdCl₂. Fatty acids were extracted from samples according to the Folch method. The fatty acid levels were determined using gas chromatography. The following fatty acids were analyzed: long-chain saturated fatty acids (SFAs) palmitic acid and stearic acid, very long-chain saturated fatty acid (VLSFA) arachidic acid, monounsaturated fatty acids (MUFAs) palmitoleic acid, oleic acid and vaccenic acid, and n-6 polyunsaturated fatty acids (PUFAs) linoleic acid and arachidonic acid. Treatment of macrophages with very low concentrations of cadmium (5–200 nM) resulted in significant reduction in the levels of arachidic, palmitoleic, oleic, vaccenic, and linoleic acids and significant increase in arachidonic acid levels (following exposure to 5 nM Cd), without significant reduction of palmitic and stearic acid levels. Treatment of macrophages with the highest tested cadmium concentration (2 μM) produced significant reduction in the levels of all examined FAs: SFAs, VLSFA, MUFAs, and PUFAs. In conclusion, cadmium at tested concentrations caused significant alterations in THP-1 macrophage fatty acid levels, disrupting their composition, which might dysregulate fatty acid/lipid metabolism thus affecting macrophage behavior and inflammatory state.     

Heavy metal-induced oxidative damage is reduced by β-estradiol application in lentil seedlings

The protective effect of β-estradiol (E) application against heavy metal (HM) toxicity in lentil (Lens culinaris) seedlings was investigated. Seeds were treated with distilled water (control) or aqueous solutions of 100 μM CdCl₂, 200 μM CuCl₂ and 1 μM E singly or in combinations (1 μM E+100 μM CdCl₂ and 1 μM E+200 μM CuCl₂). HM treatments resulted in increase in the activities of antioxidative enzymes, including superoxide dismutase (SOD), catalase (CAT), guaicol peroxidase and ascorbate peroxidase. In a similar manner, Cd and Cu affected significantly oxidative injury indicators measured as electrolyte leakage (electrical conductivity of germination medium), lipoxygenase (LOX) activity and contents of malondialdehyde (MDA; lipoperoxidation marker), carbonyl groups (protein oxidation marker) and hydrogen peroxide (a reactive oxygen species). However, E was effective in reducing HM-induced toxicity. The steroid (1) alleviated HM-induced increase in the electrolyte leakage, LOX activity and contents of MDA, carbonyl and H₂O₂ and (2) improved the activities of SOD and CAT, but not the peroxidase ones, as compared to treatments with HM singly. In addition, E application prevented HM-induced decrease in dry weight production, but did not reduce the accumulation of Cd and Cu in tissues. Results of the present study suggest that E is able to protect lentil from HM-induced oxidative damage most likely by avoidance of H₂O₂ generation and improving antioxidative enzyme activities and, thereby, decreasing oxidative stress injury, but not by reducing Cd and Cu uptake.     

Proteolytic Activity in Soybean Root Nodules : Activity in Host Cell Cytosol and Bacteroids throughout Physiological Development and Senescence

Root nodules were harvested from chamber-grown soybean (Glycine max L. Merrill cv Woodworth) plants throughout development. Apparent nitrogenase activity (acetylene reduction) peaked before seeds began to develop, but a significant amount of activity remained as the seeds matured. Nodule senescence was defined as the period in which residual nitrogenase activity was lost. During this time, soluble protein and leghemoglobin levels in the host cell cytosol decreased, and proteolytic activity against azocasein increased. Degradative changes were not detected in bacteroids during nodule senescence. Total soluble bacteroid protein per gram of nodule remained constant, and an increase in proteolytic activity in bacteroid extracts was not observed. These results are consistent with the view that soybean nodule bacteroids are capable of redifferentiation into free-living bacteria upon deterioration of the legume-rhizobia symbiosis.     

Oxidative Stress Increased in Pregnant Women with Iodine Deficiency

Iodine is an essential element trace for the synthesis of maternal thyroid hormones needed to support normal fetal development; it also acts as an antioxidant directly or induce antioxidant enzymes indirectly. Iodine deficiency and oxidative stress are associated with pregnancy complications. This study aimed to assess the urinary iodine concentration and its relationship with the antioxidant and oxidative stress status during gestation. Pregnant women were consecutively recruited from an obstetric clinic during all gestation trimesters, and urinary iodine concentration, antioxidant, and oxidative stress were determined. Results showed that 70 % of pregnant women have optimal iodine levels (150–200 μg/L), while approximately 30 % showed mild iodine deficiency (50–99 μg/L). Oxidative stress was significantly higher, and the antioxidant status was also compromised as evidenced by decreased total antioxidant status and superoxide dismutase (SOD) activity in pregnant women with mild iodine deficiency than pregnant women with optimal iodine levels. Significant positive correlations were noted between optimal iodine levels and total antioxidant status. Oxidative stress was significantly correlated with mild iodine deficiency. However, no significant correlation was found between iodine levels and SOD and catalase activities. In conclusion, for the first time, these data suggest a correlation between iodine levels and the antioxidant status during pregnancy.     

Nitric oxide increases the enzymatic activity of three ascorbate peroxidase isoforms in soybean root nodules

Ascorbate peroxidase is one of the major enzymes regulating the levels of H₂O₂ in plants and plays a crucial role in maintaining root nodule redox status. We used fully developed and mature nitrogen fixing root nodules from soybean plants to analyze the effect of exogenously applied nitric oxide, generated from the nitric oxide donor 2,2′-(hydroxynitrosohydrazono)bis-ethanimine, on the enzymatic activity of soybean root nodule ascorbate peroxidase. Nitric oxide caused an increase in the total enzymatic activity of ascorbate peroxidase. The nitric oxide-induced changes in ascorbate peroxidase enzymatic activity were coupled to altered nodule H₂O₂ content. Further analysis of ascorbate peroxidase enzymatic activity identified three ascorbate peroxidase isoforms for which augmented enzymatic activity occurred in response to nitric oxide. Our results demonstrate that nitric oxide regulates soybean root nodule ascorbate peroxidase activity. We propose a role of nitric oxide in regulating ascorbate-dependent redox status in soybean root nodule tissue.Key words: antioxidant enzymes, ascorbate peroxidase, nitric oxide, oxidative stress, reactive oxygen species, redox homeostasis, soybean root nodules     

Cadmium-induced oxidative stress in two potato cultivars

A hydroponic experiment was carried out to characterize the oxidative stress responses of two potato cultivars (Solanum tuberosum L. cvs. Asterix and Macaca) to cadmium (Cd). Plantlets were exposed to four Cd levels (0, 50, 100, 150 and 200 μM) for 7 days. Cd concentration was increased in both roots and shoot. Number of sprouts and roots was not decreased, whereas Cd treatment affected the number of nodal segments. Chlorophyll content and ALA-D activity were decreased in both cultivars, whereas carotenoids content was decreased only in Macaca. Cd caused lipid peroxidation in roots and shoot of both cultivars. Protein oxidation was only verified at the highest Cd level. H₂O₂ content was increased in roots and shoot of Asterix, and apparently, a compensatory response between roots and shoot of Macaca was observed. SOD activity was inhibited in roots of Asterix at all Cd treatments, whereas in Macaca it was only increased at two highest Cd levels. Shoot SOD activity increased in Asterix and decreased in Macaca. Root CAT activity in Asterix decreased at 100 and 150 μM, whereas in Macaca it decreased only at 50 μM. Shoot CAT activity was decreased in Macaca. Root AsA content in Macaca was not affected, whereas in shoot it was reduced at 100 μM and increased at 200 μM. Cd caused increase in NPSH content in roots and shoot. Our results suggest that Cd induces oxidative stress in both potato cultivars and that of the two cultivars, Asterix showed greater sensitivity to Cd levels.     

Accumulation of γ‐aminobutyric acid in nodulated soybean in response to drought stress

Nitrogen fixation and nodule permeability to O₂ diffusion are decreased by drought stress. Since γ‐aminobutyric acid (GABA) synthesis is rapidly stimulated by a variety of stress conditions including hypoxia, it was hypothesized that decreased O₂ availability in nodules stimulates glutamate decarboxylase (GAD) activity (EC 4.1.1.15), thereby resulting in GABA accumulation. First, the amino acid composition of xylem sap was determined in plants subjected to soil water deficits. While the xylem sap concentration of several amino acids increased when the plant was subjected to a water deficit, the greatest increase was in GABA. GABA accumulation was examined in response to stress induced by hypoxia or the addition of polyethylene glycol (PEG) to the nutrient solution. The exposure of soybean nodules to hypoxia for 6 h enhanced the GABA concentration by 6‐fold, but there was no change in GABA concentration in response to the PEG treatment. No major changes in the in vitro GAD activity were measured in nodule cytosol or bacteroids. The present data do not support the hypothesis that decreased nodule O₂ permeability and a resulting O₂ deprivation inside nodules may stimulate in vitro GAD activity and thus GABA accumulation. However, the data could indicate a possible effect of hypoxia and drought stress on the in vivo activity of GAD.     

Oxidative stress in the root nodules of Phaseolus vulgaris is induced under conditions of phosphorus deficiency

One of the most adverse effects of phosphorus (P) deficiency on N₂-fixing legumes is the generation of harmful active oxygen species which cause oxidative stress. And although oxidative stress has been widely studied in roots and shoots of various plant species, it has not yet sufficiently been documented in bean nodules so far. In this study, two recombinant inbred lines RIL115 (P-deficiency tolerant) and RIL147 (P-deficiency sensitive) of common bean and Concesa (local variety) were inoculated separately with the reference strain R. tropici CIAT899, RhM₁₁ (R. gallicum) or RhM₁₄ (R. tropici); two local strains of the Marrakesh region of Morocco. Nodulated plants were grown under semi-hydroponic conditions with sufficient or deficient P supply and analyzed for their oxidative responses at the flowering stage. The results indicated that P-deficiency decreased the growth of shoots (48 %) and nodules (32 %), particularly with RhM₁₄ exhibiting the highest decrease (52 %) of nodulation. This constraint increased electrolyte leakage of nodules (40 %) as compared to leaves (20 %), especially for plants inoculated with RhM₁₄ and CIAT899. Moreover, high H₂O₂ and malondialdehyde contents were noticed in P-deficient nodules of RhM₁₄ and RhM₁₁. These variations were associated with peroxidase activity stimulation in P-deficient nodules induced by CIAT899 and RhM₁₄. In symbiosis with RIL115, these last strains exhibited the highest nodule phenol content. Overall, phenol content was mainly enhanced in P-deficient nodules (35 %) as compared to the leaves (16 %). It was concluded that the genotypes inoculated with CIAT899 and RhM₁₁ are relatively P-deficiency tolerant combinations as compared to those inoculated with RhM₁₄. Increase of oxidative stress in nodules rather than in leaves points to the need for further investigations of mechanisms that improve the root-nodule efficiency under adverse conditions.