Ammonia emission from rice leaves in relation to photorespiration and genotypic differences in glutamine synthetase activity

Background and Aims

Rice (Oryza sativa) plants lose significant amounts of volatile NH₃ from their leaves, but it has not been shown that this is a consequence of photorespiration. Involvement of photorespiration in NH₃ emission and the role of glutamine synthetase (GS) on NH₃ recycling were investigated using two rice cultivars with different GS activities.

Methods

NH₃ emission (AER), and gross photosynthesis (P_G), transpiration (Tr) and stomatal conductance (g_S) were measured on leaves of ‘Akenohoshi’, a cultivar with high GS activity, and ‘Kasalath’, a cultivar with low GS activity, under different light intensities (200, 500 and 1000 µmol m⁻² s⁻¹), leaf temperatures (27·5, 32·5 and 37·5 °C) and atmospheric O₂ concentrations ([O₂]: 2, 21 and 40 %, corresponding to 20, 210 and 400 mmol mol⁻¹).

Key Results

An increase in [O₂] increased AER in the two cultivars, accompanied by a decrease in P_G due to enhanced photorespiration, but did not greatly influence Tr and g_S. There were significant positive correlations between AER and photorespiration in both cultivars. Increasing light intensity increased AER, P_G, Tr and g_S in both cultivars, whereas increasing leaf temperature increased AER and Tr but slightly decreased P_G and g_S. ‘Kasalath’ (low GS activity) showed higher AER than ‘Akenohoshi’ (high GS activity) at high light intensity, leaf temperature and [O₂].

Conclusions

Our results demonstrate that photorespiration is strongly involved in NH₃ emission by rice leaves and suggest that differences in AER between cultivars result from their different GS activities, which would result in different capacities for reassimilation of photorespiratory NH₃. The results also suggest that NH₃ emission in rice leaves is not directly controlled by transpiration and stomatal conductance.     

Salinity induced oxidative stress and antioxidant system in salt-tolerant and salt-sensitive cultivars of rice (Oryza sativa L.)

Indices of oxidative stress viz., superoxide radical and H₂O₂ content increased in leaves of all the cultivars with the rise in salinity level, the increase was more pronounced and significant in salt-sensitive varieties and non-significant in resistant cultivars. Except for glutathione reductase (GR), basal activities of all other antioxidative enzymes viz. superoxide dismutase (SOD), catalase (CAT), peroxidase (POX), ascorbate peroxidase (APX) and glutathione reductase (GR) were significantly higher in leaves of all the resistant cultivars as compared to the sensitive ones. A differential response of salinity was observed on various enzymatic and non-enzymatic components of antioxidant system in leaves of salt-tolerant and salt-sensitive cultivars of rice (Oryza sativa L.). Activities of superoxide dismutase and glutathione reductase enhanced in all the tolerant cultivar while declined in the sensitive cultivars with increasing salinity from 0 to 100 mM. Salt-stress induced the activities of catalase and peroxidase in all the cultivars but the magnitude of increase was more pronounced in the sensitive cultivars than in the tolerant cultivars. Contrarily, APX activity increased in the salt-sensitive cultivars but showed no significant change in the salt-tolerant cultivars. The amount of ascorbic acid content, reduced glutathione (GSH), reduced/oxidized glutathione (GSSG) ratio was higher in leaves of the tolerant cultivars than that of the sensitive cultivars under saline conditions. It is inferred that leaves of salt-tolerant cultivars tend to attain greater capacity to perform reactions of antioxidative pathway under saline conditions to combat salinity-induced oxidative stress.     

Oxidative stress, protein carbonylation, proteolysis and antioxidative defense system as a model for depicting water deficit tolerance in Indica rice seedlings

Water deficit is an important constraint to rice (Oryza sativa L.) productivity. The present study was undertaken to investigate whether the level of oxidative stress, carbonylation of proteins, proteolysis and status of antioxidative defense could serve as a model to distinguish water deficit tolerant and sensitive rice cultivars. When 10-day-grown seedlings of two rice cultivars, Malviya-36 (drought-sensitive) and Brown Gora (drought-tolerant) were subjected to ?1.0 and ?2.1 MPa water deficit treatments for 24–72 h with polyethylene glycol 6000 in the medium, a greater decline in the growth of the seedlings and levels of leaf water potential, relative water content, Chl a, Chl b, carotenoids and greater increase in leaf water loss were observed in the sensitive cultivar than the tolerant. Under similar level of water deficit seedlings of sensitive cultivar showed higher level of superoxide anion generation, H₂O₂, lipid peroxidation and proteolysis in roots as well as shoots compared to the tolerant. Drought-tolerant cultivar had higher constitutive level of antioxidative enzymes superoxide dismutase and catalase and the activities of these two enzymes alongwith of guaiacol peroxidase showed greater increase in this cultivar under water deficit compared to the sensitive. A significant decline in the level of protein thiol and a higher increase in protein carbonyls content, also confirmed by protein gel blot analysis with an antibody against 2,4-dinitrophenylhydrazine was observed in the seedlings of drought sensitive cv. Malviya-36 compared to the tolerant cv. Brown Gora when subjected to similar level of water deficit. Seedlings of drought sensitive cultivar, under water deficit, showed higher proteolytic activity, higher number of in-gel activity stained proteolytic bands and higher expression of oxidized proteins in roots compared to the tolerant cultivar. Results suggest that poor capacity of antioxidative enzymes could be, at least partly, correlated with water deficit sensitivity of sensitive cultivar and that higher activity of antioxidative enzymes superoxide dismutase, catalase, guaiacol peroxidase, low proteolytic activity, lower level of protein carbonyls and protein thiolation could serve as a model to depict water deficit tolerance in Indica rice seedlings.     

Root antioxidant responses of two Pisum sativum cultivars to direct and induced Fe deficiency

The contribution of antioxidant defence systems in different tolerance to direct and bicarbonate‐induced Fe deficiency was evaluated in two pea cultivars (Kelvedon, tolerant and Lincoln, susceptible). Fe deficiency enhanced lipid peroxidation and H₂O₂ concentration in roots of both cultivars, particularly in the sensitive one grown under bicarbonate supply. The results obtained on antioxidant activities (SOD, CAT, POD) suggest that H₂O₂ accumulation could be due to an overproduction of this ROS and, at the same time, to a poor capacity to detoxify it. Moreover, under bicarbonate supply the activity of POD isoforms was reduced only in the sensitive cultivar, while in the tolerant one a new isoform was detected, suggesting that POD activity might be an important contributor to pea tolerance to Fe deficiency. The presence of bicarbonate also resulted in stimulation of GR, MDHAR and DHAR activities, part of the ASC‐GSH pathway, which was higher in the tolerant cultivar than in the sensitive one. Overall, while in the absence of Fe only slight differences were reported between the two cultivars, the adaptation of Kelvedon to the presence of bicarbonate seems to be related to its greater ability to enhance the antioxidant response at the root level.     

Foliar abscisic acid content underlies genotypic variation in stomatal responsiveness after growth at high relative air humidity

Background and Aims

Stomata formed at high relative air humidity (RH) respond less to abscisic acid (ABA), an effect that varies widely between cultivars. This study tested the hypotheses that this genotypic variation in stomatal responsiveness originates from differential impairment in intermediates of the ABA signalling pathway during closure and differences in leaf ABA concentration during growth.

Methods

Stomatal anatomical features and stomatal responsiveness to desiccation, feeding with ABA, three transduction elements of its signalling pathway (H₂O₂, NO, Ca²⁺) and elicitors of these elements were determined in four rose cultivars grown at moderate (60 %) and high (90 %) RH. Leaf ABA concentration was assessed throughout the photoperiod and following mild desiccation (10 % leaf weight loss).

Key Results

Stomatal responsiveness to desiccation and ABA feeding was little affected by high RH in two cultivars, whereas it was considerably attenuated in two other cultivars (thus termed sensitive). Leaf ABA concentration was lower in plants grown at high RH, an effect that was more pronounced in the sensitive cultivars. Mild desiccation triggered an increase in leaf ABA concentration and equalized differences between leaves grown at moderate and high RH. High RH impaired stomatal responses to all transduction elements, but cultivar differences were not observed.

Conclusions

High RH resulted in decreased leaf ABA concentration during growth as a result of lack of water deficit, since desiccation induced ABA accumulation. Sensitive cultivars underwent a larger decrease in leaf ABA concentration rather than having a higher ABA concentration threshold for inducing stomatal functioning. However, cultivar differences in stomatal closure following ABA feeding were not apparent in response to H₂O₂ and downstream elements, indicating that signalling events prior to H₂O₂ generation are involved in the observed genotypic variation.     

Growth stage-based modulation in antioxidant defense system and proline accumulation in two hexaploid wheat (Triticum aestivum L.) cultivars differing in salinity tolerance

Changes in the antioxidant defense system and proline accumulation were examined at different growth stages (vegetative, boot and reproductive) in plants of two hexaploid spring wheat cultivars (S-24, salt tolerant; MH-97, salt sensitive), grown in hydroponics and salinity-affected with 0, 50, 100 and 150 mM of NaCl. Salt stress provoked a marked decline in plant dry mass and ascorbic acid contents, and increased proline, total soluble proteins and H₂O₂ contents in both wheat cultivars at all growth stages. However, higher accumulation of proline and H₂O₂ contents was recorded at the vegetative and boot stages, respectively, in both wheat cultivars. Salt stress caused a consistent rise in the activities of some key antioxidant enzymes (CAT, SOD, POD, and APX) at all growth stages only in the salt tolerant cultivar S-24, whereas such pattern of enhanced activities of enzymatic antioxidants in cv. MH-97 was found only at the vegetative stage under saline regimes. Maximum activities of various enzymatic antioxidants were observed at the vegetative stage in both wheat cultivars under varying external salt treatments. The results showed that high salinity tolerance of cv. S-24, as manifested by lower decrease in its dry matter under salt stress, was associated with higher activities of antioxidant enzymes, increased accumulation of proline, and lower levels of H₂O₂, as compared with cv. MH-97 at all growth stages under saline regimes.     

Salicylic Acid,as a Positive Regulator of Isochorismate Synthase,Reduces the Negative Effect of Salt Stress on Pistacia vera L. by Increasing Photosynthetic Pigments and Inducing Antioxidant Activity

Salinity, as a serious and prevalent abiotic stress, causes widespread crop losses by restricting plant growth and production throughout the world. In this study, the biochemical and molecular responses of the pistachio (Pistacia vera L.) plant were studied under NaCl and salicylic acid (SA) treatments using hydroponically grown salt tolerant (Ghazvini) and salt sensitive (Sarakhs) pistachio cultivars. NaCl treatment (250 mM) increased the production of hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) and the activity of antioxidant enzymes in both cultivars. In the sensitive cultivar, the H₂O₂ content was higher than the tolerant cultivar, especially in the roots. SA application to both salt-stress-treated cultivars resulted in an increase in photosynthetic pigment contents and antioxidant enzyme activity and a decrease in the H₂O₂ and MDA contents. After NaCl treatment, the isochorismate synthase (ICS) gene was upregulated in Ghazvini which leads to an increase in the SA content of the salt tolerant pistachio cultivar. In contrast, the salt treatment downregulated the expression of the ICS gene in Sarakhs. The ICS gene expression was positively regulated by SA treatment under the salt stress condition. Our results suggest that Ghazvini has higher salinity tolerance than Sarakhs due to its higher antioxidant capacity, photosynthetic pigment content, and the cultivar-specific expression pattern of the ICS gene. In this study, the potential alleviative effects of SA on the adverse effect of salt stress in P. vera (Pistacia vera) were also identified and highlighted.

     

Arsenic-induced oxidative stress in the common bean legume,Phaseolus vulgaris L. seedlings and its amelioration by exogenous nitric oxide

The adverse effects of arsenic (As) toxicity on seedling growth, root and shoot anatomy, chlorophyll and carotenoid contents, root oxidizability (RO), antioxidant enzyme activities, H₂O₂ content, lipid peroxidation and electrolyte leakage (EL%) in common bean (Phaseolus vulgaris L.) were investigated. The role of exogenous nitric oxide (NO) in amelioration of As-induced inhibitory effect was also evaluated using sodium nitroprusside (100 μM SNP) as NO donor and 2-(4-carboxy-2-phenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (200 μM PTIO) as NO scavenger in different combinations with 50 μM As. As-induced growth inhibition was associated with marked anomalies in anatomical features, reduction in pigment composition, increased RO and severe perturbations in antioxidant enzyme activities. While activity of superoxide dismutase and catalase increased, levels of ascorbate peroxidase, dehydroascorbate reductase and glutathione reductase decreased significantly and guaiacol peroxidase remained normal. The over-accumulation of H₂O₂ content along with high level of lipid peroxidation and electrolyte leakage indicates As-induced oxidative damage in P. vulgaris seedlings with more pronounced effect on the roots than the shoots. Exogenous addition of NO significantly reversed the As-induced oxidative stress, maintaining H₂O₂ in a certain level through balanced alterations of antioxidant enzyme activities. The role of NO in the process of amelioration has ultimately been manifested by significant reduction of membrane damage and improvement of growth performance in plants grown on As + SNP media. Onset of oxidative stress was more severe after addition of PTIO, which confirms the protective role of NO against As-induced oxidative damage in P. vulgaris seedlings.     

Exogenous application of thiamin promotes growth and antioxidative defense system at initial phases of development in salt-stressed plants of two maize cultivars differing in salinity tolerance

The effects of thiamin (Thi) applied as seed soaking or foliar spray on some key physiological parameters were investigated in two differentially salt-responsive maize (Zea mays L.) cultivars, DK 5783 and Apex 836 F1, exposed to saline stress in two different experiments. An initial experiment (germination experiment) was designed to identify appropriate doses of Thi which could lessen the deleterious effects of salt on plants and screen all available maize cultivars for their differential tolerance to salt stress (100 mM NaCl). The seeds of nine maize cultivars were soaked for 24 h in solutions containing six levels of Thi (25, 50, 75, 100, 125 and 150 mg l^?1). Based on the results obtained from the germination experiment, maize cultivar DK 5783 was found to be the most salt tolerant and Apex 836 as the most sensitive cultivar. Also, of six Thi levels used, two levels (100 and 125 mg l^?1) were chosen for subsequent studies. In the second experiment (glasshouse experiment), two maize cultivars, DK 5783 (salt tolerant) and Apex 836 (salt sensitive) were subjected to saline regime (100 mM NaCl) and two levels of Thi (100 and 125 mg l^?1) applied as foliar spray. Salt stress markedly suppressed shoot and root dry mass, total chlorophylls (“a” + “b”), leaf water potential and maximum fluorescence yield (Fv/Fm) in the plants of both maize cultivars, but it increased proline accumulation, leaf osmotic pressure, malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) concentrations, electrolyte leakage (EL) as well as activities of some key antioxidant enzymes, superoxide dismutase (SOD; EC. 1.15.1.1), peroxidase (POD; EC. 1.11.1.7) and catalase (CAT; EC. 1.11.1.6). Salt-induced reduction in plant growth parameters was higher in the salt-sensitive cultivar, Apex 836, which was found to be associated with relatively increased EL, and MDA and H₂O₂ levels, and decreased activities of the key antioxidant enzymes. Application of Thi as seed soaking or foliar spray partly mitigated the deleterious effects of salinity on plants of both maize cultivars. The most promising effect of Thi on alleviation of adverse effects of salt stress on maize plants was found when it was applied as foliar spray at 100 mg l^?1. Thiamin application considerably reduced tissue Na⁺ concentration, but improved those of N, P, Ca²⁺ and K⁺ in the salt-stressed maize plants. Exogenously applied thiamin-induced growth improvement in maize plants was found to be associated with reduced membrane permeability, MDA and H₂O₂ levels, and altered activities of some key antioxidant enzymes such as CAT, SOD and POD as well as increased photosynthetic pigment concentration under saline regime.     

Characterization of growth and Oryctes rhinoceros nudivirus production in attached cultures of the DSIR-HA-1179 coleopteran insect cell line

The DSIR-HA-1179 coleopteran cell line is a susceptible and permissive host to the Oryctesrhinoceros nudivirus (OrNV), which has been used as a biocontrol agent against the coconut rhinoceros beetle (Oryctes rhinoceros); a pest of palms in the Asia-Pacific region. However, little is known about growth and metabolism of this cell line, knowledge of which is necessary to develop an in vitro large-scale OrNV production process. The strong anchorage-dependent characteristics of the cell line, its particular fragility and its tendency to form dense clumps when manipulated, are the most likely reasons that have precluded further development of the cell line. In order to characterize DSIR-HA-1179 cells, there was first a need for a reliable technique to count the cells. A homogenous cell suspension suitable for enumeration could be produced by treatment with TrypLE Express™ with optimum mean time for cell release calculated as 30 min. The cell line was adapted to grow in four serum-supplemented culture media namely TC-100, IPL-41, Sf-900 II and Sf-900 III and cell growth, glucose consumption, lactate and ammonia production were assessed from static-batch cultures. The maximum viable cell density was reached in Sf-900 II (17.9 × 10⁵ cells/ml), with the maximum specific growth rate observed in this culture medium as well (0.0074 h⁻¹). Higher production of OrNV was observed in IPL-41 and TC-100 (4.1 × 10⁷ TCID₅₀/ml) than in cultures infected in Sf-900 III (2.0 × 10⁷ TCID₅₀/ml) and Sf-900 II (1.4 × 10⁷ TCID₅₀/ml). At the end of the growth period, glucose was completely consumed in cultures grown in TC-100, while remained in excess in the other three culture media. The cell line produced lactate and ammonia to very low levels in the TC-100 culture medium which is a promising aspect for its cultivation at large-scale.     

Cultivar Differences in Photosynthetic Tolerance to Photooxidation and Shading in Rice (Oryza Sativa L.)

Forty-four genotypes from the rice germplasm were identified under photoinhibition/photooxidation and shade conditions and divided into four basic types: (1) cultivars tolerant to both photooxidation and shading, (2) cultivars tolerant to photooxidation but sensitive to shading, (3) cultivars tolerant to shading but sensitive to photooxidation, and (4) cultivars sensitive to both photooxidation and shading. Photosynthetic characteristics of a cultivar tolerant (cv. Wuyugeng 3) and a cultivar sensitive (cv. Xiangxian) to photooxidation and shading were compared. The photochemical efficiency (F_v/F_m) of photosystem 2 (PS2) and the content of PS2-D1 protein in the tolerant cultivar Wuyugeng 3 decreased less under photooxidative conditions as compared with Xiangxian. Under similar conditions, superoxide dismutase was induced rapidly to a higher activity and the active oxygen (O^–) built up to a lower level in Wuyugeng 3 than in Xiangxian. Net photosynthetic rate (P _N) decreased by 23 % in Wuyugeng 3 vs. 64 % in Xiangxian. Shading (80 %) during the booting stage caused only small decreases (7–13 %) in ribulose-1,5-bisphosphate carboxylase activity and P _N in Wuyugeng 3 but severe decreases (57–64 %) were observed in Xiangxian which corresponded to the decreases in grain yield of the two cultivars (38 and 73 %, respectively). We described a simple and effective screening method and physiological basis for breeding crops for enhanced tolerance to both high and low irradiance.     

Use of Enzymatic Biosensors to Quantify Endogenous ATP or H2O2 in the Kidney

Enzymatic microelectrode biosensors have been widely used to measure extracellular signaling in real-time. Most of their use has been limited to brain slices and neuronal cell cultures. Recently, this technology has been applied to the whole organs. Advances in sensor design have made  possible the measuring of cell signaling in blood-perfused in vivo kidneys. The present protocols list the steps needed to measure ATP and H₂O₂ signaling in the rat kidney interstitium. Two separate sensor designs are used for the ex vivo and in vivo protocols. Both types of sensor are coated with a thin enzymatic biolayer on top of a permselectivity layer to give fast responding, sensitive and selective biosensors. The permselectivity layer protects the signal from the interferents in biological tissue, and the enzymatic layer utilizes the sequential catalytic reaction of glycerol kinase and glycerol-3-phosphate oxidase in the presence of ATP to produce H₂O₂. The set of sensors used for the ex vivo studies further detected analyte by oxidation of H₂O₂ on a platinum/iridium (Pt-Ir) wire electrode. The sensors for the in vivo studies are instead based on the reduction of H₂O₂ on a mediator coated gold electrode designed for blood-perfused tissue. Final concentration changes are detected by real-time amperometry followed by calibration to known concentrations of analyte. Additionally, the specificity of the amperometric signal can be confirmed by the addition of enzymes such as catalase and apyrase that break down H₂O₂ and ATP correspondingly. These sensors also rely heavily on accurate calibrations before and after each experiment. The following two protocols establish the study of real-time detection of ATP and H₂O₂ in kidney tissues, and can be further modified to extend the described method for use in other biological preparations or whole organs.     

Elucidating Cd-mediated distinct rhizospheric and in planta ionomic and physio-biochemical responses of two contrasting Zea mays L. cultivars

Cadmium (Cd) in soil–plant system can abridge plant growth by initiating alterations in root zones. Hydroponics and rhizoboxes are useful techniques to monitor plant responses against various natural and/or induced metal stresses. However, soil based studies are considered more appropriate in order to devise efficient food safety and remediation strategies. The present research evaluated the Cd-mediated variations in elemental dynamics of rhizospheric soil together with in planta ionomics and morpho-physio-biochemical traits of two differentially Cd responsive maize cultivars. Cd-sensitive (31P41) and Cd-tolerant (3062) cultivars were grown in pots filled with 0, 20, 40, 60 and 80 µg/kg CdCl₂ supplemented soil. The results depicted that the maize cultivars significantly influenced the elemental dynamics of rhizosphere as well as in planta mineral accumulation under applied Cd stress. The uptake and translocation of N, P, K, Ca, Mg, Zn and Fe from rhizosphere and root cell sap was significantly higher in Cd stressed cv. 3062 as compared to cv. 31P41. In sensitive cultivar (31P41), Cd toxicity resulted in significantly prominent reduction of biomass, leaf area, chlorophyll, carotenoids, protein contents as well as catalase activity in comparison to tolerant one (3062). Analysis of tolerance indexes (TIs) validated that cv. 3062 exhibited advantageous growth and efficient Cd tolerance due to elevated proline, phenolics and activity of antioxidative machinery as compared to cv. 31P41. The cv. 3062 exhibited 54% and 37% less Cd bio-concentration (BCF) and translocation factors (TF), respectively in comparison to cv. 31P41 under highest Cd stress regime. Lower BCF and TF designated a higher Cd stabilization by tolerant cultivar (3062) in rhizospheric zone and its potential use in future remediation plans.     

The influence of cold acclimation on antioxidative enzymes and antioxidants in sensitive and tolerant barley cultivars

In order to better understand the role of cold acclimation in alleviating freezing injury, two barley cultivars with different cold tolerance, i.e. a sensitive cv. Chumai 1 and a tolerant cv. Mo 103, were used. The freezing treatment increased leaf soluble protein content more in the tolerant cultivar than in the sensitive one. Cold acclimation increased H₂O₂ content of the two cultivars during freezing treatment, especially in Mo 103. Glutathione and ascorbate contents during freezing and recovery were significantly higher in cold-acclimated plants than in non-acclimated ones. Activities of peroxidase, ascorbate peroxidase and glutathione reductase were also higher in cold-acclimated plants than non-acclimated plants during freezing treatment. However, there was no significant difference between cold-acclimated plants and the control plants in catalase activity. It may be assumed that cold acclimation induced H₂O₂ production, which in turn enhanced activities of antioxidative enzymes and synthesis of antioxidants, resulting in alleviation of oxidative stress caused by freezing.     

Chemolithotrophic acetogenic H2/CO2 utilization in Italian rice field soil

Acetate oxidation in Italian rice field at 50 °C is achieved by uncultured syntrophic acetate oxidizers. As these bacteria are closely related to acetogens, they may potentially also be able to synthesize acetate chemolithoautotrophically. Labeling studies using exogenous H₂ (80%) and ¹³CO₂ (20%), indeed demonstrated production of acetate as almost exclusive primary product not only at 50 °C but also at 15 °C. Small amounts of formate, propionate and butyrate were also produced from ¹³CO₂. At 50 °C, acetate was first produced but later on consumed with formation of CH₄. Acetate was also produced in the absence of exogenous H₂ albeit to lower concentrations. The acetogenic bacteria and methanogenic archaea were targeted by stable isotope probing of ribosomal RNA (rRNA). Using quantitative PCR, ¹³C-labeled bacterial rRNA was detected after 20 days of incubation with ¹³CO₂. In the heavy fractions at 15 °C, terminal restriction fragment length polymorphism, cloning and sequencing of 16S rRNA showed that Clostridium cluster I and uncultured Peptococcaceae assimilated ¹³CO₂ in the presence and absence of exogenous H₂, respectively. A similar experiment showed that Thermoanaerobacteriaceae and Acidobacteriaceae were dominant in the ¹³C treatment at 50 °C. Assimilation of ¹³CO₂ into archaeal rRNA was detected at 15 °C and 50 °C, mostly into Methanocellales, Methanobacteriales and rice cluster III. Acetoclastic methanogenic archaea were not detected. The above results showed the potential for acetogenesis in the presence and absence of exogenous H₂ at both 15 °C and 50 °C. However, syntrophic acetate oxidizers seemed to be only active at 50 °C, while other bacterial groups were active at 15 °C.     

An inductive pulse of hydrogen peroxide pretreatment restores redox-homeostasis and oxidative membrane damage under extremes of temperature in two rice cultivars

Imbibitional heat and chilling stress caused disruption of redox-homeostasis and oxidative damage to newly assembled membrane system by aggravating membrane lipid peroxidation and protein oxidation [measured in terms of thiobarbituric acid reactive substances (TBARS), free carbonyl content (C=O groups) and membrane protein thiol level (MPTL)] along with concomitant increase in accumulation of reactive oxygen species (superoxide and hydrogen peroxide) and significant reduction of antioxidative defense (assessed in terms of total thiol content and activities of superoxide dismutase, catalase, ascorbate peroxidase and glutathione reductase) in both the salt sensitive (Ratna) and resistant (SR 26B) germinating tissues of rice cultivars. When compared, salt resistant cultivar SR 26B found to suffer significantly less oxidative membrane damage as compared to salt sensitive cultivar Ratna. Treatment with low titer of hydrogen peroxide caused significant reversal in oxidative damages to the newly assembled membrane system imposed by imbibitional heat and chilling stress (evident from the data of TBARS, C=O, MPTL, ROS accumulation, membrane permeability status, membrane injury index and oxidative stress index) in seedlings of both the cultivars of rice (Ratna and SR 26B). Imbibitional H₂O₂ pretreatment also caused up-regulation of antioxidative defense (activities of superoxide dismutase, catalase, ascorbate peroxidase, glutathione reductase and total thiol content) in the heat and chilling stress-raised seedlings of experimental rice cultivars. When the parameters of early growth performances were assessed (in terms of relative growth index, biomass accumulation and vigor index), it clearly exhibited significant improvement of early growth performances of both the rice cultivars. Better response towards H₂O₂-mediated acclamatory performances and restoration of redox- homeostasis under extremes of temperature were noticed in salt sensitive rice cultivar Ratna compared to salt resistant SR 26B. Taken as a whole, the result suggests the significance of the role of ‘inductive pulse’ of H₂O₂ in acclimatizing adverse temperature stress by restoration of redox-homeostasis and mitigation of oxidative membrane protein and lipid damages during the recovery phase of post-germination event.     

Relative salinity tolerance of rice cultivars native to North East India: a physiological,biochemical and molecular perspective

Salinity is the second most prevalent abiotic stress faced by plants, and rice is not an exception. Through this study, it has been tried upon, to study the relative salinity tolerance of eight local varieties of North East India. Preliminary screening was based on their dose- and time-dependent physiological responses to salinity stress. Among the cultivars, Tampha was found to be relatively more tolerant, whereas MSE9 the most sensitive. To further ascertain their tolerance capacity, MDA and H₂O₂ content was determined, which also confirmed the tolerance level of the two cultivars. Histochemical assays for root plasma membrane integrity and leaf and root H₂O₂ and O₂ ^? content also showed more damage in Tampha in comparison to MSE9. Finally, gene expression analysis for Na⁺/K⁺ co-transporters, OsHKT2;1, OsHKT2;3 and OsHKT2;4, was performed to observe how the expression level of these transporters varies with the tolerance capacity of these two cultivars in leaves and roots under different time frames. The study reveals Tampha to be the most tolerant and MSE9 the most sensitive when compared to the other six screened cultivars for salinity stress.     

Responses of the antioxidative enzymes in Malaysian rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.) cultivars under submergence condition

The potential involvement of activated oxygen species by submergence stress was studied in two Malaysian rice cultivars, MR219-4 and MR219-9, and cultivar FR13A that is known to be tolerant to submergence. Seedlings of these three rice cultivars were subjected to different submergence periods (4, 8, and 12 days). Under 8 days of complete submergence, FR13A cultivar showed higher lipid peroxidation in terms of malondialdehyde level and activities of antioxidative enzymes, superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR) when compared to the MR219-4 and MR219-9 cultivars. MR219-9 showed higher SOD, APX, and GR activities after 12 days of submergence. The levels of SOD activity indicated that detoxification of O₂^·− to H₂O₂ was maintained at a stable level throughout the submergence stress until up to 8 days and increased rapidly at 12 days of submergence. The results indicated that tolerance to submergence in rice is associated until 8 days submergence for MR219-4 and FR13A cultivars. These findings suggested that tolerance to submergence stress in rice might be proven by increased the capacity of antioxidative system. In addition, CAT activity has much higher affinity for scavenges H₂O₂ than APX. Therefore, ascorbate glutathione cycle might be more efficient to scavenge H₂O₂.     

Mycotoxin-Producing Ability and Chemotype Diversity of Aspergillus Section Flavi from Soils of Peanut-Growing Regions in Iran

Invasion of crops with Aspergillus flavus may result in contamination of food and feed with carcinogenic mycotoxins such as aflatoxins (AF) and cyclopiazonic acid (CPA). In the present study, distribution and toxigenicity of Aspergillus flavus and A. parasiticus in soils of five peanut fields located in Guilan province, Northern Iran was investigated. From a total of 30 soil samples, 53 strains were isolated which all of them were finally identified as A. flavus by a combination of colony morphology, microscopic criteria and mycotoxin profiles. Chromatographic analysis of fungal cultures on yeast extract sucrose broth by tip culture method showed that 45 of the 53 A. flavus isolates (84.9 %) were able to produce either CPA or AFB₁, while eight of the isolates (15.1 %) were non-toxigenic. The amounts of CPA and AFB₁ produced by the isolates were reported in the range of 18.2–403.8 μg/g and 53.3–7446.3 μg/g fungal dry weights, respectively. Chemotype classification of A. flavus isolates based on the ability for producing mycotoxins and sclerotia showed that 43.4 % were producers of CPA, AFB₁ and sclerotia (group I), 13.2 % of CPA and AFB₁ (group II), 9.4 % of AFB₁ and sclerotia (group III), 13.2 % of AFB₁ (group IV), 5.7 % of CPA and sclerotia (group V) and 15.1 % were non-toxigenic with no sclerotia (group VI). No strain was found as producer of only CPA or sclerotia. These results indicate different populations of mycotoxigenic A. flavus strains enable to produce hazardous amounts of AFB₁ and CPA are present in peanuts field soils which can be quite important regard to their potential to contaminate peanuts as a main crop consumed in human and animal nutrition.