Nitrogen supplying ability of some Philippine rice soils

Summary The nitrogen-supplying power of eight Philippine rice soils was measured by consecutively growing six crops of IR 32 rice under flooded conditions in a greenhouse pot experiment. The dry matter yields or nitrogen uptake of rice were found to be highly positively correlated with the organic carbon and the total nitrogen contents of the soils, as well as with the amounts of ammonium released during an anaerobic incubation test at 30°C for 2 weeks.The results of the study bring out the usefulness of simple tests like organic carbon content and total nitrogen content of soils for predicting the nitrogen-supplying power to lowland rice.     

Modification of the acid permanganate method for obtaining an index of soil nitrogen availability

Summary The acid permanganate method proposed as a chemical index of soil nitrogen (N) availability simply measures the mineralizable N. A modification of the method has been proposed that allows the estimation of soil mineral N simultaneously. The N values obtained by the modified method correlated highly significantly with the mineral N of incubation test (r=0.80,P<0.01) and plant uptake (r=0.69,P<0.01).     

H2 oxidation,O2 uptake and CO2 fixation in hydrogen treated soils

In many legume nodules, the H₂ produced as a byproduct of N₂ fixation diffuses out of the nodule and is consumed by the soil. To study the fate of this H₂ in soil, a H₂ treatment system was developed that provided a 300 cm³ sample of a soil:silica sand (2:1) mixture with a H₂ exposure rate (147 nmol H₂ cm^–3hr^–1) similar to that calculated exist in soils located within 1–4 cm of nodules (30–254 nmol H₂ cm^–3hr^–1). After 3 weeks of H₂ pretreatment, the treated soils had a K_m and V_max for H₂ uptake (1028 ppm and 836 nmol cm^–3 hr^–1, respectively) much greater than that of control, air-treated soil (40.2 ppm and 4.35 nmol cm^–3 hr^–1, respectively). In the H₂ treated soils, O₂, CO₂ and H₂ exchange rates were measured simultaneously in the presence of various pH₂. With increasing pH₂, a 5-fold increase was observed in O₂ uptake, and CO₂ evolution declined such that net CO₂ fixation was observed in treatments of 680 ppm H₂ or more. At the H₂ exposure rate used to pretreat the soil, 60% of the electrons from H₂ were passed to O₂, and 40% were used to support CO₂ fixation. The effect of H₂ on the energy and C metabolism of soil may account for the well-known effect of legumes in promoting soil C deposition.     

Silk sericin protein of tropical tasar silkworm inhibits UVB-induced apoptosis in human skin keratinocytes

The silk protein sericin has been identified as a potent antioxidant and photoprotective agent against ultraviolet B (UVB) irradiation in mouse skin model. In this study, we have investigated the anti-apoptotic effect of sericin in UVB (30 mJ/cm²)-irradiated human keratinocytes. Flow cytometry analysis has shown that pre-treatment with sericin inhibits UVB-induced apoptosis. The pre-treatment with sericin suppresses bax expression, up-regulates the expression of bcl-2, prevents both the activation of caspase-3 and cleavage of Poly (ADP-ribose) polymerase. Generation of intracellular hydrogen peroxide in UVB-treated keratinocytes is inhibited through pre-treatment with sericin suggesting that sericin probably prevents mitochondrial damage. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Contribution of N2 fixing cyanobacteria to rice production: availability of nitrogen from 15N-labelled cyanobacteria and ammonium sulphate to rice

This study investigate the potential contribution of nitrogen fixation by indigenous cyanobacteria to rice production in the rice fields of Valencia (Spain). N₂-fixing cyanobacteria abundance and N₂ fixation decreased with increasing amounts of fertilizers. Grain yield increased with increasing amounts of fertilizers up to 70 kg N ha^-1. No further increase was observed with 140 kg N ha^-1. Soil N was the main source of N for rice, only 8–14% of the total N incorporated by plants derived from ¹⁵N fertilizer. Recovery of applied ¹⁵N-ammonium sulphate by the soil–plant system was lower than 50%. Losses were attributed to ammonia volatilization, since only 0.3–1% of applied N was lost by denitrification. Recovery of ¹⁵N from labeled cyanobacteria by the soil–plant system was higher than that from chemical fertilizers. Cyanobacterial N was available to rice plant even at the tillering stage, 20 days after N application. This revised version was published online in June 2006 with corrections to the Cover Date.     

Vitamin E-enriched diet reduces adaptive responses to training determining respiratory capacity and redox homeostasis in rat heart

We investigated whether reactive oxygen species (ROS) are involved in heart adaptive responses administering a vitamin E-enriched diet to trained rats. Using the homogenates and/or mitochondria from rat hearts we determined the aerobic capacity, tissue level of mitochondrial proteins, and expression of cytochrome c and factors (PGC-1, NRF-1, and NRF-2) involved in mitochondrial biogenesis. We also determined the oxidative damage, glutathione peroxidase (GPX) and reductase activities, glutathione content, mitochondrial ROS release rate, and susceptibility to in vitro oxidative challenge. Glutathione (GSH) content was not affected by both training and antioxidant supplementation. Conversely, antioxidant supplementation prevented metabolic adaptations to training, such as the increases in oxidative capacity, tissue content of mitochondrial proteins, and cytochrome c expression, attenuated some protective adaptations, such as the increase in antioxidant enzyme activities, and did not modify the decrease in ROS release by succinate supplemented mitochondria. Moreover, vitamin E prevented the training-linked increase in tissue capacity to oppose an oxidative attach. The antioxidant effects were associated with decreased levels of PGC-1, NRF-1, and NRF-2 expression. Our results support the idea that some heart adaptive responses to training depend on ROS produced during the exercise sessions and are mediated by the increase in PGC-1 expression which is involved in both the regulation of respiratory capacity and antioxidant protection. However, vitamin inability to prevent some adaptations suggests that other signaling pathways impinging on PGC-1 can modify the response to the antioxidant integration.     

The inductive responses of the antioxidant enzymes by salt stress in the rice (Oryza sativa L.)

To access contributions of inductive responses of the antioxidant enzymes in the resistance to salt stress, activities of the enzymes were determined in the rice (Oryza sativaL. cv. Dongjin) plant. In the leaves of the rice plant, salt stress preferentially enhanced the content of H₂O₂ as well as the activities of the superoxide dismutase (SOD), ascorbate peroxidase (APX), and peroxidase specific to guaiacol, whereas it induced the decrease of catalase activity. On the other hand, salt stress had little effect on the activity levels of glutathione reductase (GR). In order to analyze the changes of antioxidant enzyme isoforms against salt stress, plant extracts were subjected to native PAGE. Leaves of the rice plant had two isoforms of Mn-SOD and five isoforms of Cu/Zn-SOD. Fe-SOD isoform was not observed in the activity gels. Expression of Cu/Zn-1, -2, and Mn-SOD-2 isoforms was preferentially enhanced by salt stress. Seven APX isoforms were presented in the leaves of the rice plants. The intensities of APX-4 to -7 were enhanced by salt stress, whereas those of APX-1 to -3 were minimally in changed response to salt stress. There were seven GR isoforms in the leaves of rice plants. Levels of activity for most GR isoforms did not change in the stressed plants compared to the control plants. On the other hand, the levels of activity for most antioxidant enzymes changed little in the roots of stressed plants compared to the control plants. These results collectively suggest that SOD leads to the overproduction of hydrogen peroxide in the leaves of rice plants subjected to salt stress: The overproduction of hydrogen peroxide functions as the signal of salt stress, which induces the induction of specific APX isoforms but not specific GR isoforms under catalase deactivation.     

Evaluation of laboratory-based measures of soil mineral nitrogen and potentially mineralizable nitrogen as predictors of field-based indices of soil nitrogen supply in potato production

Accurate estimation of soil nitrogen (N) supply in the field is required to optimize fertilizer N management and to minimize environmental N losses in humid environments. Laboratory-based measures of N availability were evaluated as predictors of field-based indices of soil N supply within potato production systems. Pre-plant soil samples (0–15 cm) were collected from a series of forty treatments in established potato trials located in Atlantic Canada and Maine, USA. Total plant N uptake at topkill with no fertilizer N applied (PNU_0N), PNU_0N plus soil mineral N to 30 cm depth at harvest and relative yield were considered as field-based indices of soil N supply. The potentially mineralizable N (N₀) was determined by aerobic incubation at 25°C and periodic leaching for 24 weeks. A series of laboratory-based measures of soil N supply were measured in soil samples. Pre-plant soil nitrate or total mineral N at 0–30 cm depth was the best single predictor of PNU_0N (r = 0.67 and 0.71, respectively) and relative yield (r = 0.58 and 0.61). The ultraviolet absorbance of 0.01 M NaHCO₃ extract at 205 nm (NaHCO₃-205) was suitable as a predictor of PNU_0N and relative yield in each growing season, however, the relationship between this parameter and PNU_0N or relative yield varied somewhat among years. A combination of pre-plant mineral N plus N mineralized in the first 2 weeks period of incubation after re-wetting is proposed as a more robust measure of N availability compared with use of mineral N alone.     

Acclimation of nitrogen uptake capacity of rice to elevated atmospheric CO2 concentration

Background and Aims: Nitrogen (N) is a major factor affecting yield gain of cropsunder elevated atmospheric carbon dioxide concentrations [CO₂].It is well established that elevated [CO₂] increases root mass,but there are inconsistent reports on the effects on N uptakecapacity per root mass. In the present study, it was hypothesizedthat the responses of N uptake capacity would change with theduration of exposure to elevated [CO₂]. Methods: The hypothesis was tested by measuring N uptake capacity inrice plants exposed to long-term and short-term [CO₂] treatmentsat different growth stages in plants grown under non-limitingN conditions in hydroponic culture. Seasonal changes in photosynthesisrate and transpiration rate were also measured. Key Results: In the long-term [CO₂] study, leaf photosynthetic responsesto intercellular CO₂ concentration (Ci) were not affected byelevated [CO₂] before the heading stage, but the initial slopein this response was decreased by elevated [CO₂] at the grain-fillingstage. Nitrate and ammonium uptake capacities per root dry weightwere not affected by elevated [CO₂] at panicle initiation, butthereafter they were reduced by elevated [CO₂] by 31–41% at the full heading and mid-ripening growth stages. In theshort-term study (24 h exposures), elevated [CO₂] enhanced nitrateand ammonium uptake capacities at the early vegetative growthstage, but elevated [CO₂] decreased the uptake capacities atthe mid-reproductive stage. Conclusions: This study showed that N uptake capacity was downregulated underlong-term exposure to elevated [CO₂] and its response to elevated[CO₂] varied greatly with growth stage.     

Determination of sulphite in mineral soils

Summary Two methods were evaluated to determine the concentration of sulphite in sandy loam soils. Use of p-rosaniline-formaldehyde reagent and sodium tetrachloromercurate as extractant proved effective only if a wide soil to extractant ratio was employed. Use of Ellman's reagent in conjunction with this extractant was however, unsatisfactory. Soils exposed to heavy atmospheric pollution differed in sulphite concentration only marginally compared with relatively unpolluted soils. The effect of soil water content on the stability of sulphite in soil was also determined.     

Salt and paraquat stress tolerance results from co-expression of the Suaeda salsa glutathione S-transferase and catalase in transgenic rice

GST (Glutathione S-transferase, EC 2.5.1.18) and CAT (Catalase, EC 1.11.1.6) play important roles in oxidative stress resistance. In this study, we transferred both GST and CAT1 of Suaeda salsa into rice (Oryza sativa cv. Zhonghua No.11) by Agrobacterium tumefaciens-mediated transformation under the control of cauliflower mosaic virus (CaMV) 35S promoter, and investigated whether co-expressing the GST and CAT1 in transgenic rice could reduce oxidative damage. Salt and paraquat stresses were applied. The data showed that co-expression of the GST and CAT1 resulted in greater increase of CAT and SOD (Superoxide Dismutase, EC 1.15.1.1) activity in the transgenics compared to non-transgenics following both stress imposition. Whereas the significant increase of GST activity in transgenics only occurred in paraquat stressed plants. While the generation of H₂O₂, Malon dialdehyde and plasma membrane relative electrolyte leakage decreased in the transgenics than in non-transgenics under the same conditions. Moreover, the transgenic rice seedlings showed markedly enhanced tolerance to salt stress compared with non-transgenics upon 200 mM NaCl treatment in greenhouse. The enhancement of the active oxygen-scavenging system that led to increased oxidative stress protection in GST + CAT1-transgenic rice plants could result not only from increased GST and CAT activity but also from the combined increase in SOD activity.     

Protective effects of sulfated chitooligosaccharides against hydrogen peroxide-induced damage in MIN6 cells

Sulfated chitooligosaccharides (COS-S) with different degrees of substitution (DS) were obtained by the chlorosulfuric acid/pyridine method. Protective effects of COS-S against hydrogen peroxide (H₂O₂)-induced damage were investigated in pancreatic β-cells MIN6 cell line. The cell viability, morphology, insulin contents, malondialdehyde (MDA) inhibition, lactate dehydrogenase (LDH) release and the levels of antioxidant enzymes including catalase (CAT), superoxide dismutase (SOD) and glutathione peroxidise (GPx) were evaluated under oxidative damage by 150 μM H₂O₂ for 6 h. COS-S did not show any harmful or inhibitory effect on cell growth at concentrations ranging from 0.1 to 0.5 mg/ml. While COS-S could enhance the cell viability, decrease the production of ROS, and reduce the MDA level as well as LDH level in oxidative damaged β-cells by being an antioxidant. The underlining mechanisms of protective effects of COS-S are partly due to the enhancement of antioxidant enzyme activity and inhibition of intracellular ROS production, along with suppressing MIN6 cell apoptosis subsequent to the amelioration of ROS. Moreover, increased DS might contribute to the defense mechanisms against H₂O₂-induced oxidative damage in MIN6 cells. These results indicated that the antioxidant properties of COS-S hold great potential for the oxidative diseases treatment, and the sulfate content of polysaccharides made great role in regulating antioxidant activities.     

Oxidative stress enhances phosphorylation of p53 in neonatal rat cardiomyocytes

p53 is an important regulator of cell growth and apoptosis and its activity is regulated by phosphorylation. Accordingly, in neonatal rat cardiomyocytes we examined the involvement of p53 in H₂O₂-induced apoptosis. Treatment with 50–100 μM H₂O₂ markedly induced apoptosis in cardiomyocytes, as assessed by gel electrophoresis of genomic DNA. To examine whether H₂O₂ increases p53 phosphorylation in cardiomyocytes, we utilized an antibody that specifically recognizes phosphorylated p53 at serine-15. The level of phosphorylated p53 was markedly increased by 100 μM H₂O₂ at 30 and 60 min. Using specific protein kinase inhibitors we examined the involvement of protein kinases in p53 phosphorylation in response to H₂O₂ treatment. However, staurosporine, a broad spectrum inhibitor of protein kinases, SB202190, a specific p38 kinase inhibitor, PD98059, a MAP kinase inhibitor, wortmannin, an inhibitor of DNA-PK and PI3 kinase, SP600125, a JNK inhibitor and caffeine,an inhibitor of ATM and ATR, failed to prevent the H₂O₂-induced phosphorylation of p53. cDNA microarray revealed that H₂O₂ markedly increased expression of several p53 upstream modifiers such as the p300 coactivator protein and several downstream effectors such as gadd45, but decreased the expression of MDM2, a negative regulator of p53. Our results suggest that phosphorylation of p53 at serine-15 may be an important signaling event in the H₂O₂-mediated apoptotic process.     

Suppressive effect of H2O2 on increase in activities of acid invertases in rye roots

Although various effects of H₂O₂ on plant cellular functions have been reported, the effects of H₂O₂ on glycolytic enzymes remain unknown. It was shown that H₂O₂ has a suppressive effect on increase in activities of soluble and insoluble acid invertases among a number of glycolytic enzymes during a growth stage of rye roots.     

Effect of urea placement on leaching losses of nitrogen from flooded rice soils

In an effort to provide an explanation for the reported variability in fertilizer N efficiency from deepplaced urea on flooded rice, a set of controlled experiments was conducted to evaluate the effect of water percolation on fertilizer loss and plant uptake from¹⁵N labeled urea supergranules. Three soils of different texture (silt loam-clay) were subjected to various percolation rates (0–20 mm/day) while planted to rice which was harvested after approximately 40 days.The results indicate that moderate to high percolation through silt loam soil will lead to significant fertilizer N losses and drastically decrease the fertilizer uptake by plants. The permeability of the clay soil was too low for any leaching to take place. It is therefore concluded that deep placement of urea supergranules not be recommended in soils where percolation rates may exceed 5 mm/day, particularly if the cation exchange capacity of the soil is low. This experiment points to the need of evaluating and reporting the percolation rates in soils where experiments with supergranular urea are conducted.Contribution from the Agro-Economic Division of the International Fertilizer Development Center (IFDC), Muscle Shoals, Alabama 35660.     

Antioxidant activity of vasoactive intestinal peptide in HK2 human renal cells

Oxidative stress is a major mediator of tissue and cell injuries. The injury in chronic nephrotic syndrome, acute renal failure, myeloma kidney injury and other kidney diseases is initiated by oxidative stress. We have previously demonstrated that vasoactive intestinal peptide (VIP) acts as an antiproliferative agent in renal cancer cells. This study was designed to evaluate the renoprotective activity of VIP against H₂O₂-induced oxidative damage in a proximal tubule kidney cell line (human, non-tumor, HK2 cells) in order to investigate the potential usefulness of this peptide in the treatment of oxidative-stress related kidney diseases. HK2 cell viability was assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay. Propidium iodide was used to identify cells undergoing apoptosis. Western blotting was performed with anti-Bcl-2, anti-Bax and anti-formyl peptide receptor (low-affinity variant FPRL-1) monoclonal antibodies whereas 2,7-dichlorofluorescein diacetate was used for measurement of levels of intracellular reactive oxygen species (ROS). HK2 cells were injured with H₂O₂ in order to induce apoptosis: the effect was time- and dose-dependent. VIP increased the levels of the antiapoptotic protein Bcl-2 and decreased those of the proapoptotic protein Bax. VIP decreased the intracellular ROS levels reached by H₂O₂-induced oxidative stress. VIP effect on ROS levels involved FPLR-1 but not VPAC_1,2 receptors as evidenced by the use of the respective antagonists WRW4 and JV-1-53. Thus, VIP protects HK2 cells from apoptosis by increasing Bcl-2 levels and this effect is initiated through FPLR1 receptor. In conclusion, VIP might exert a renoprotective effect by the suppression of oxidative stress.     

Error caused by carbon dioxide in determination of ammonium by direct steam distillation of tropical wetland rice soils

Summary A study was made with eight Philippine wetland rice soils to quantify the possible error caused by the CO₂ evolved during direct distillation of soil suspensions in aerobic and anaerobic conditions with MgO. The error caused by CO₂ was eliminated by absorbing the ammonia distilled in H₂SO₄, which was gently boiled to derive off the CO₂ absorbed. The possible error caused by CO₂ was not eliminated when boric acid was used for absorbing ammonia. The difference in NH₄ ⁺ values determined by using sulfuric acid and boric acid methods gave an estimate of the error caused by CO₂. It was found that CO₂ evolved caused negative error in the NH₄ ⁺ values obtained using the direct distillation of soil suspensions with MgO in presence of KCl. The magnitude of error was higher and significant with anaerobic soil samples but this error was negligible with aerobic soils.     

Transgenically expressed rice germin-like protein1 in tobacco causes hyper-accumulation of H2O2 and reinforcement of the cell wall components

Our recent report documented that the rice germin-like protein1 (OsGLP1), being a cell wall-associated protein involves in disease resistance in rice and possesses superoxide dismutase (SOD) activity as recognized by heterologous expression in tobacco. In the present study, the transgenic tobacco plants were analyzed further to decipher the detailed physiological and biochemical functions of the OsGLP1 and its associated SOD activity. The transgenic tobacco lines expressing SOD-active OsGLP1 showed tolerance against biotic and abiotic stresses mitigated by hyper-accumulating H₂O₂ upon infection by fungal pathogen (Fusarium solani) and treatment to chemical oxidizing agent (ammonium persulfate), respectively. Histological staining revealed enhanced cross-linking of the cell wall components in the stem tissues of the transgenic plants. Fourier transform infrared spectroscopy (FTIR) analysis of the biopolymer from the stem tissues of the transgenic and untransformed plants revealed differential banding pattern of the spectra corresponding to various functional groups. Our findings demonstrate that the OsGLP1 with its inherent SOD activity is responsible for hyper-accumulation of H₂O₂ and reinforcement of the cell wall components.     

Differential responses of rice to inoculation with wild-type and non-pathogenic mutants of Magnaporthe oryzae

We analyzed the response of rice to Magnaporthe oryzae infection using two mutant strains deficient in Mgb1 and Mst12, which are essential for the development of appresoria and penetration pegs. Both mutants induced the much lower levels of accumulation of phytoalexins than wild-type, suggesting that the massive production of phytoalexins requires the fungal invasion of rice cells. Intense accumulation of H₂O₂ in a single whole cell also required fungal penetration. Microarray analysis of rice gene expression revealed mutant-specific gene expression, indicating that signal exchange between rice and M. oryzae commence before fungal penetration of the rice cell. In situ detection of mRNAs for peroxidase and β-1,3-glucanase showed that expression of these genes also occurs after penetration as observed for phytoalexin production. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Tomoaki Kato, Shigeru Tanabe, and Marie Nishimura contributed equally to this work. Accession number of the original microarray data in NCBI is GSE9450.