Roots Of Rice Seedlings Research Articles

Lack of ACTPK1, an STY kinase, enhances ammonium uptake and use, and promotes growth of rice seedlings under sufficient external ammonium

Ammonium influx into plant roots via the high-affinity transport system (HATS) is down-modulated under elevated external ammonium, preventing ammonium toxicity. In ammonium-fed Arabidopsis, ammonium transporter 1 (AMT1) trimers responsible for HATS activity are allosterically inactivated in a dose-dependent manner via phosphorylation of the conserved threonine at the carboxyl-tail by the calcineurin B-like protein 1-calcineurin B-like protein-interacting protein kinase 23 complex and other yet unidentified protein kinases. Using transcriptome and reverse genetics in ammonium-preferring rice, we revealed the role of the serine/threonine/tyrosine protein kinase gene OsACTPK1 in down-modulation of HATS under sufficient ammonium. In wild-type roots, ACTPK1 mRNA and protein accumulated dose-dependently under sufficient ammonium. To determine the function of ACTPK1, two independent mutants lacking ACTPK1 were produced by retrotransposon Tos17 insertion. Compared with segregants lacking insertions, the two mutants showed decreased root growth and increased shoot growth under 1mm ammonium due to enhanced ammonium acquisition, via aberrantly high HATS activity, and use. Furthermore, introduction of OsACTPK1 cDNA fused to the synthetic green fluorescence protein under its own promoter complemented growth and the HATS influx, and suggested plasma membrane localization. Root cellular expression of OsACTPK1 also overlapped with that of ammonium-induced OsAMT1;1 and OsAMT1;2. Meanwhile, threonine-phosphorylated AMT1 levels were substantially decreased in roots of ACTPK1-deficient mutants grown under sufficient ammonium. Bimolecular fluorescence complementation assay further confirmed interaction between ACTPK1 and AMT1;2 at the cell plasma membrane. Overall, these findings suggest that ACTPK1 directly phosphorylates and inactivates AMT1;2 in rice seedling roots under sufficient ammonium.

Effects of Azospirillum brasilense and Pseudomonas fluorescens on nitrogen transformation and enzyme activity in the rice rhizosphere

Azospirillum brasilense (A. brasilense) and Pseudomonas fluorescens (P. fluorescens) have long been known to benefit inoculated rice plants, but their effects on nitrogen (N) transformations and enzyme activities in the rice rhizosphere are unclear. This study explored whether A. brasilense and P. fluorescens are involved in modifying N transformations, N-supplying capacity, and enzyme activities in the rice rhizosphere, and the performance of rice biomass after inoculation with A. brasilense and P. fluorescens was also evaluated. Rice inoculation was conducted under pot culture conditions in 2014 and 2015, and the experiment included four treatments: a control (CT), rice seedling roots inoculated with A. brasilense (Mb), rice seedling roots inoculated with P. fluorescens (Mp), and rice seedling roots inoculated with a mixture of A. brasilense and P. fluorescens (Mbp). The rice variety used in this trial was Zhongzheyou 1 (Indica). To explore the effects of A. brasilense and P. fluorescens strains on N transformations and enzyme activities in the rice rhizosphere, N fertilizer was not applied in this trial, while the full doses of P (150 mg P2O5 per pot) and K (320 mg K2O per pot) were applied. Inoculating the rice rhizosphere with A. brasilense and P. fluorescens greatly improved the ammonification activities in the soil, and the effects were more favorable in the Mbp treatment. However, the contribution of inoculation to the nitrification activity in the rhizosphere was poor. Compared to CT, the average mineralized N content in the Mbp, Mb, and Mp treatments was increased by 165.7, 110.2, and 88.5%, respectively. Co-inoculation with A. brasilense and P. fluorescens in the rice rhizosphere greatly increased the nitrogenase activities in the soil, and inoculating with A. brasilense alone in the rice rhizosphere also showed good results. The microbial biomass N and enzyme activities were positively related to the N transformations in the soil. Finally, rice biomass increased greatly after A. brasilense and P. fluorescens inoculation in the rhizosphere. Inoculating A. brasilense and P. fluorescens in the rice rhizosphere accelerated N transformations and improved the N-supplying capacity of the rhizosphere soil, and increased rice biomass. The most beneficial effects were observed with A. brasilense and P. fluorescens co-inoculation in the rice rhizosphere.

Nitric oxide enhances selenium concentration by promoting selenite uptake by rice roots

AbstractNitric oxide (NO) plays a key role in regulating a wide range of physiological and biochemical processes. This study investigated possible effects of NO, which was supplied by sodium nitroprusside (SNP), NO donor, on selenium (Se) concentration, Se species within roots, activities and gene transcription of selenite uptake, and metabolism‐related transporters or enzymes using ICP‐MS, HPLC‐ICP/MS, qRT‐PCR, fluorescence imaging, and biochemical analysis in the roots of rice (Oryza sativa L.) seedling. A suitable SNP concentration (10 µM) increased Se concentration in rice roots. NO enhanced the gene transcription of phosphate transporter OsPT2 and sulfate transporters OsSultr1;2 and OsSultr4;1 that contribute to selenite uptake. Furthermore, NO increased selenocysteine and methyl‐selenocysteine concentrations in roots, stimulated glutathione biosynthesis by up‐regulating the transcript levels of γ‐glutamylcysteine synthetase (γ‐ECS) and glutathione synthetase (GS), and increased cysteine synthase (CS) activity. In conclusion, our results indicate that NO promotes Se concentration of rice seedling roots by enhancing selenite uptake, up‐regulating gene transcription of selenite uptake‐related transporters, and increasing Se metabolism through regulating glutathione biosynthesis.

Foliar application of aspartic acid lowers cadmium uptake and Cd-induced oxidative stress in rice under Cd stress.

Cadmium (Cd) contamination of farmland soils is a widespread problem around the globe, and rice (Oryza sativa L.) tends to accumulate more Cd and is considered as one of the major sources of Cd intake in humans, especially consuming rice-derived products. The current study investigated the effects of foliar applied aspartic acid (Asp) on growth parameters, biomass, chlorophyll concentration, gas exchange characteristics, Cd uptake, and antioxidative capacity in the shoots and roots of rice seedlings exposed to Cd stress. For this, 30-day-old rice nursery was transferred in the soil with aged Cd contamination (2.86mgkg-1). After 2weeks of growth, different concentrations (0, 10, 15, and 20mgL-1) of Asp were foliar applied four times with a 7-day interval, and the crop was harvested after 10weeks of transplanting. Foliar applied Asp increased the plant height, shoot and root dry weight, chlorophyll concentration, and gas exchange parameters, while it reduced the Cd concentrations in both shoots and roots as well as shoot to root Cd translocation factor compared to the control. Foliar application of Asp reduced the malondialdehyde content and electrolyte leakage in rice parts compared to the control in a dose-additive manner. The activities of key antioxidant enzymes increased while peroxidase activity decreased by exogenous Asp. The increase in plant weight and photosynthesis might be due to lower Cd concentrations in plants which may reduce the oxidative stress and also help the plants to minimize direct damage caused by Cd to the photosynthetic organs.

Effect of corrosion inhibitor benzotriazole on the uptake and translocation of Cd in rice (Oryza sativa L.) under different exposure conditions

Emerging contaminants that can complex with heavy metals might affect the speciation of coexisting metals and result in different ecological risks. As a widely used metal corrosion inhibitor, 1H-benzotriazole (BTR) is frequently detected in the environments, sometimes at very high levels. In this study, rice (Oryza sativa L.) was used to assess the ecological risk of combined exposure to cadmium (Cd) and BTR in plants and discuss the potential effects of exposure sequence on the uptake and translocation of Cd under hydroponic culture. In the combined exposure treatments, Cd concentration in rice significantly decreased when the molar ratio of BTR to Cd exceeded 1, while the oxidative damage of root was alleviated. In the sequential exposure treatments, an exposure to BTR accelerated the release of preabsorbed Cd from seedlings to the environment and increased the transport of Cd from the roots to shoots at high BTR concentrations. This demonstrates that the combined pollution effect of Cd and BTR is present not only in the environment but also in plants. With the decrease in Cd concentration in the roots, the electrolytic leakages from the roots also decreased, indicating that root damage repair was induced by the subsequent BTR exposure. BTR was mainly accumulated in the seedling roots. Preabsorbed BTR significantly increased Cd concentration in the roots of rice seedlings but inhibited Cd translocation from the roots to shoots of the rice seedlings.

English

Weed has become one of the most serious problems in dry seeded rice (DSR). To increase the competitiveness with weeds and achieve the optimum growth of rice, weed management in DSR needs an integration of herbicides and optimum nitrogen (N) fertilizer rates. In this study, the bioassay species were treated with a series of pre-emergence (pretilachlor and pendimethalin) and early post-emergence (propanil+thiobencarb) herbicide concentrations and N fertilizer. It was found that pretilachlor at an application rate of 0.25 and 0.50 kg ai ha-1 almost completely inhibit the emergence and shoot growth of E. indica by 100% inhibition, at 50, 100 and 150 kg ha-1 N, respectively, but it showed severe injury symptom to the root of rice seedlings. Meanwhile, pendimethalin and N fertilizer at moderate application rate gave a strong reduction of weed emergence (>50% inhibition) and shoot fresh weight (>85% inhibition), with negligible effect on the rice seedlings growth. Significant inhibitory effects on weed emergence (60% inhibition) and shoot growth (90% inhibition) also were noticed at the highest application rate of propanil + thiobencarb (3.6 kg ai ha-1) and N fertilizer (150 kg ha-1 N), with stimulation effects on the growth of rice seedlings. This promising effect showed combination of propanil + thiobencarb and N fertilizer (3.60 kg ai ha-1 propanil + thiobencarb + 150 kg ha-1 N) was the most efficient treatment for E. indica control in dry seeded rice. Key words: Eleusine indica, herbicides, N fertilizer, dry seeded rice.

Transcriptome Analysis of Rice Seedling Roots in Response to Potassium Deficiency

Rice is one of the most important food crops in the world, and its growth, development, yield, and grain quality are susceptible to a deficiency of the macronutrient potassium (K+). The molecular mechanism for K+ deficiency tolerance remains poorly understood. In this study, K+ deficient conditions were employed to investigate the resulting changes in the transcriptome of rice seedling roots. Using ribonucleic acid sequencing (RNA-Seq) and analysis, a total of 805 differentially expressed genes were obtained, of which 536 genes were upregulated and 269 were downregulated. Gene functional classification showed that the expression of genes involved in nutrient transport, protein kinases, transcription processes, and plant hormones were particularly altered in the roots. Although these changes were significant, the expression of most genes remained constant even in K+-deficient conditions. Interestingly, when our RNA-Seq results were compared to public microarray data, we found that most of the genes that were differentially expressed in low K+ conditions also exhibited changes in expression in other environmental stress conditions.

The role of exogenous proline in amelioration of lipid peroxidation in rice seedlings exposed to Cr(VI)

Lipid peroxidation was hydroponically investigated in rice seedlings (Oryza sativa L. cv. XZX 45) treated with different doses of hexavalent chromium (Cr(VI)) in the presence or absence of exogenous proline. Results showed that Cr(VI) induced lipid peroxidation was observed as indicated by higher accumulation of malondialdehyde (MDA) in roots of rice seedlings without application of proline. Cr(VI) also caused inhibition of relative growth rate and increase of root cell death of rice seedlings compared with control. Additionally, changes of roots phenotype traits were evident in roots of rice seedlings under Cr(VI) stress. Exogenous proline significantly increased Cr accumulation in roots, compared with rice seedings without proline treatment. However, less lipid peroxidation was detected in proline-treated rice seedlings as displayed by decreases in MDA content and root cell viability. Hierarchical cluster analysis was also performed using varieties of Cr accumulation, MDA content, root viability and root phenotype traits to further elucidate the role of exogenous proline in amelioration of lipid peroxidation. It is suggestive from the present study that exogenous proline is able to effectively reduce Cr(VI)-induced lipid peroxidation in rice seedlings.

水稲幼植物根中のグルタミンシンテターゼの性質と細胞内分布 : 植物の窒素吸収同化過程におけるグルタミンの役割(第3報)

水稲幼植物根中のグルタミンシンテターゼの性質と細胞内分布 : 植物の窒素吸収同化過程におけるグルタミンの役割(第3報)

植物によるNO_3-N利用に関する研究(第3報) : NO_3-N供給の開始または停止による植物根の硝酸還元と各種体内成分の消長について

植物によるNO_3-N利用に関する研究(第3報) : NO_3-N供給の開始または停止による植物根の硝酸還元と各種体内成分の消長について

L‐cysteine desulfhydrase‐related H2S production is involved in OsSE5‐promoted ammonium tolerance in roots of Oryza sativa

Previous studies revealed that rice heme oxygenase PHOTOPERIOD SENSITIVITY 5 (OsSE5) is involved in the regulation of tolerance to excess ammonium by enhancing antioxidant defence. In this study, the relationship between OsSE5 and hydrogen sulfide (H2 S), a well-known signalling molecule, was investigated. Results showed that NH4 Cl triggered the induction of l-cysteine desulfhydrase (l-DES)-related H2 S production in rice seedling roots. A H2 S donor not only alleviated the excess ammonium-triggered inhibition of root growth but also reduced endogenous ammonium, both of which were aggravated by hypotaurine (HT, a H2 S scavenger) or dl-propargylglycine (PAG, a l-DES inhibitor). Nitrogen metabolism-related enzymes were activated by H2 S, thus resulting in the induction of amino acid synthesis and total nitrogen content. Interestingly, the activity of l-DES, as well as the enzymes involved in nitrogen metabolism, was significantly increased in the OsSE5-overexpression line (35S:OsSE5), whereas it impaired in the OsSE5-knockdown mutant (OsSE5-RNAi). The application of the HT/PAG or H2 S donor could differentially block or rescue NH4 Cl-hyposensitivity or hypersensitivity phenotypes in 35S:OsSE5-1 or OsSE5-RNAi-1 plants, with a concomitant modulation of nitrogen assimilation. Taken together, these results illustrated that H2 S function as an indispensable positive regulator participated in OsSE5-promoted ammonium tolerance, in which nitrogen metabolism was facilitated.

Auxin transport and response requirements for root hydrotropism differ between plant species.

The direction of auxin transport changes in gravistimulated roots, causing auxin accumulation in the lower side of horizontally reoriented roots. This study found that auxin was similarly involved in hydrotropism and gravitropism in rice and pea roots, but hydrotropism in Lotus japonicus roots was independent of both auxin transport and response. Application of either auxin transport inhibitors or an auxin response inhibitor decreased both hydrotropism and gravitropism in rice roots, and reduced hydrotropism in pea roots. However, Lotus roots treated with these inhibitors showed reduced gravitropism but an unaltered or an enhanced hydrotropic response. Inhibiting auxin biosynthesis substantially reduced both tropisms in rice and Lotus roots. Removing the final 0.2 mm (including the root cap) from the root tip inhibited gravitropism but not hydrotropism in rice seedling roots. These results suggested that modes of auxin involvement in hydrotropism differed between plant species. In rice roots, although auxin transport and responses were required for both gravitropism and hydrotropism, the root cap was involved in the auxin regulation of gravitropism but not hydrotropism. Hydrotropism in Lotus roots, however, may be regulated by a novel mechanism that is independent of both auxin transport and the TIR1/AFBs auxin response pathway.

Morpho-physiological analysis of tolerance to aluminum toxicity in rice varieties of North East India.

Aluminum (Al) is the third most abundant metal in earth crust, whose chemical form is mainly dependent on soil pH. The most toxic form of Al with respect to plants is Al3+, which exists in soil pH <5. Acidic soil significantly limits crop production mainly due to Al3+ toxicity worldwide, impacting approximately 50% of the world’s arable land (in North-Eastern India 80% soil are acidic). Al3+ toxicity in plants ensues root growth inhibition leading to less nutrient and water uptake impacting crop productivity as a whole. Rice is one of the chief grains which constitutes the staple food of two-third of the world population including India and is not untouched by Al3+ toxicity. Al contamination is a critical constraint to plant production in agricultural soils of North East India. 24 indigenous Indica rice varieties (including Badshahbhog as tolerant check and Mashuri as sensitive check) were screened for Al stress tolerance in hydroponic plant growth system. Results show marked difference in growth parameters (relative growth rate, Root tolerance index, fresh and dry weight of root) of rice seedlings due to Al (100 μM) toxicity. Al3+ uptake and lipid peroxidation level also increased concomitantly under Al treatment. Histochemical assay were also performed to elucidate uptake of aluminum, loss of membrane integrity and lipid peroxidation, which were found to be more in sensitive genotypes at higher Al concentration. This study revealed that aluminum toxicity is a serious harmful problem for rice crop productivity in acid soil. Based on various parameters studied it’s concluded that Disang is a comparatively tolerant variety whereas Joymati a sensitive variety. Western blot hybridization further strengthened the claim, as it demonstrated more accumulation of Glutathione reductase (GR) protein in Disang rice variety than Joymati under stressed condition. This study also observed that the emergence of lethal toxic symptoms occurs only after 48h irrespective of the dose used in the study.

Effects of silicon on Oryza sativa L. seedling roots under simulated acid rain stress.

Silicon (Si) has an important function in reducing the damage of environmental stress on plants. Acid rain is a serious abiotic stress factor, and Si can alleviate the stress induced by acid rain on plants. Based on these assumptions, we investigated the effects of silicon on the growth, root phenotype, mineral element contents, hydrogen peroxide (H2O2) and antioxidative enzymes of rice (Oryza sativa L.) seedling roots under simulated acid rain (SAR) stress. The results showed that the combined or single effects of Si and/or SAR on rice roots depend on the concentration of Si and the pH of the SAR. The combined or single effects of a low or moderate concentration of Si (1.0 or 2.0 mM) and light SAR (pH 4.0) enhanced the growth of rice roots, and the combined effects were stronger than those of the single treatment. A high concentration of Si (4.0 mM) or severe SAR (pH 2.0) exerted deleterious effects. The incorporation of Si (1.0, 2.0 or 4.0 mM) into SAR with pH 3.0 or 2.0 promoted the rice root growth, decreased the H2O2 content, increased the Si concentration and the superoxide dismutase (SOD), catalase (CAT), peroxidase (POD) and ascorbate peroxidase (APX) activities, maintained the balance of mineral element (K, Ca, Mg, Fe, Zn, and Cu) concentrations in the roots of rice seedlings compared with SAR alone. The alleviatory effects observed with a moderate concentration of Si (2.0 mM) were better than the effects obtained with a low or high concentration of Si (1.0 or 4.0 mM). The observed effects were due to disruptions in the absorption and utilization of mineral nutrients and impacts on the activity of antioxidant enzymes in roots, and this conclusion suggests that the degree of rice root damage caused by acid rain might be attributed to not only acid rain but also the level of Si in the soil.

Overexpression of GSK3-like Kinase 5 (OsGSK5) in rice (Oryza sativa) enhances salinity tolerance in part via preferential carbon allocation to root starch.

Rice (Oryza sativa L.) is very sensitive to soil salinity. To identify endogenous mechanisms that may help rice to better survive salt stress, we studied a rice GSK3-like isoform (OsGSK5), an orthologue of a Medicago GSK3 previously shown to enhance salinity tolerance in Arabidopsis by altering carbohydrate metabolism. We wanted to determine whether OsGSK5 functions similarly in rice. OsGSK5 was cloned and sequence, expression, evolutionary and functional analyses were conducted. OsGSK5 was expressed highest in rice seedling roots and was both salt and sugar starvation inducible in this tissue. A short-term salt-shock (150mM) activated OsGSK5, whereas moderate (50mM) salinity over the same period repressed the transcript. OsGSK5 response to salinity was due to an ionic effect since it was unaffected by polyethylene glycol. We engineered a rice line with 3.5-fold higher OsGSK5 transcript, which better tolerated cultivation on saline soils (EC=8 and 10dSm-2). This line produced more panicles and leaves, and a higher shoot biomass under high salt stress than the control genotypes. Whole-plant 14C-tracing and correlative analysis of OsGSK5 transcript with eco-physiological assessments pointed to the accelerated allocation of carbon to the root and its deposition as starch, as part of the tolerance mechanism.

Impact of TiO2 nanoparticles on lead uptake and bioaccumulation in rice (Oryza sativa L.)

Titanium dioxide nanoparticles (TiO2 NPs) are among the most widely used metal oxide nanoparticles, and their release into the environment is inevitable. The impact of this NPs release on the fate and toxicity of coexisting heavy metals is largely unknown. In this work, a series of hydroponic experiments were conducted to investigate impact of four types of TiO2 NPs, including one anatase (NAnT), one pristine rutile (NRuT) and two rutiles with hydrophilic and hydrophobic surfaces (NLRuT, NBRuT), as well as the bulk particles (BT), on the bioaccumulation of lead (Pb) by rice (Oryza sativa) seedlings. The results indicate that TiO2 NPs exposure at the levels of 10 and 1000mg/L had no significant adverse effects on the growth and development of rice seedlings. Due to its small crystallite size (252.2Å), only one type of TiO2 NPs (NAnT) entered rice seedling roots through an apoplastic route. However, NAnT particles were not translocated from roots to shoots, likely due to the obstruction effects of casparian strip in the root tissues. Both nano and bulk TiO2 reduced the bioaccumulation of Pb in rice at high TiO2 exposure levels (1000mg/L) but the extent of the reduction was TiO2-type dependent. NAnT, NRuT and NLRuT reduced the Pb concentration in rice roots by >80% and by 77–97% in shoots, likely due to the particles high sorption potential for Pb in the nutrient solution. NBRuT and BT reduced Pb levels by 45–61% in roots and 11–38% in shoots. Although NAnT was able to effectively reduce the bioaccumulation of Pb in rice tissues, this particle did accumulate in rice roots, which poses a potential risk to food safety. Accordingly, NAnT is not recommended for Pb pollution control. NRuT and NLRuT are more appropriate agents to reduce Pb contamination threats to rice plants, which in turn may mitigate health risk to humans through the food chain.

Responses of endogenous proline in rice seedlings under chromium exposure

Hydroponic experiments were performed to exam the dynamic change of endogenous proline in rice seedlings exposed to potassium chromate chromium (VI) or chromium nitrate chromium (III). Although accumulation of both chromium species in rice seedlings was obvious, more chromium was detected in plant tissues of rice seedlings exposed to chromium (III) than those inchromium (VI), majority being in roots rather than shoots. Results also showed that the accumulation capacity of chromium by rice seedlings was positively correlated to chromium concentrations supplied in both chromium variants and the accumulation curve depicted an exponential trend in both chromium treatments over the entire period of exposure. Proline assays showed that both chromium variants induced the change of endogenous proline in shoots and roots of rice seedlings. Chromium (VI) of 12.8 mg/L increased proline content significantly ( p<0.05) compared to control, while the effect of chromium (III) on proline content was more evident at 30.0 mg/L ( p<0.05). The results collected here suggest that both chromium variants are able to cause the change of endogenous proline in rice seedlings, but the response was found to be different between the two chromium treatments.

Lanthanum regulates the reactive oxygen species in the roots of rice seedlings

In this study, the effects of La3+ on the reactive oxygen species (ROS) and antioxidant metabolism were studied in the roots of rice (Oryza sativa L. cv Shengdao 16) exposed to increasing concentrations of La3+ (0.05, 0.1, 0.5, 1.0, and 1.5 mM). The level of hydrogen peroxide, superoxide anion, and malondialdehyde was increased by 0.5, 1.0 and 1.5 mM La3+, and the activity of catalase and peroxidase was increased by 0.05 and 0.1 mM La3+. However, La3+ treatments stimulated superoxide dismutase activity in the roots of rice seedlings at all tested concentrations. In addition, the probe 2′,7′-dichlorofluorescein diacetate (H2DCF-DA) was used to investigate the instantaneous change of ROS in the root cells with the laser-scanning confocal microscopy. The result indicated that ROS level was declined after treated with 0.05 mM La3+. The results showed that the appropriate concentration of La3+ decreased the level of ROS, and hormetic effects on the antioxidant metabolism were found in the roots of rice exposed to 0.05, 0.1, 0.5, 1.0, and 1.5 mM La3+.

Hemin-mediated alleviation of zinc, lead and chromium toxicity is associated with elevated photosynthesis, antioxidative capacity; suppressed metal uptake and oxidative stress in rice seedlings

In this study, we investigated the possible role of hemin in alleviating zinc (Zn), lead (Pb) and chromium (Cr) toxicity in rice seedlings grown hydroponically by analyzing the morphological and physiological parameters. Our results showed that exposure of rice seedlings to excess Zn, Pb or Cr could cause severe leaf chlorosis, inhibit photosynthetic activity and consequently suppress plant growth. The concentration of O2 •− and H2O2 significantly increased and the activities of antioxidative enzymes decreased in roots of rice seedlings under metal exposure. The combined treatments (hemin + ZnSO4, hemin + Pb(NO3)2 and hemin + K2Cr2O7), on the other hand, significantly enhanced the photosynthesis- and plant growth-related parameters compared with their corresponding heavy-metal-stress alone. Combined treatments dramatically stimulated the activities of superoxide dismutase (SOD), ascorbic peroxidase (APX) and glutathione reductase (GR) as well as the concentrations of ascorbic acid (AsA) and glutathione (GSH) as compared with the metal- stress alone. The concentrations of reactive oxygen species (ROS, e.g. O2 •− and H2O2) were significantly reduced in the metal plus hemin treatments. Hemin addition also reduced metal accumulation in rice seedlings especially in root tissues. These findings suggest that hemin-elevated levels of antioxidants, activities of antioxidative enzymes and hemin-reduced accumulation of heavy-metal could confer resistance against Zn, Pb, and Cr stress in rice seedlings, resulting in improved pigments accumulation, photosynthetic attributes and plant growth.

Genome-wide transcriptome analysis of expression in rice seedling roots in response to supplemental nitrogen

Nitrogen (N) is the most important macronutrient for plant growth and grain yields. For rice crops, nitrate and ammonium are the major N sources. To explore the genomic responses to ammonium supplements in rice roots, we used 17-day-old seedlings grown in the absence of external N that were then exposed to 0.5mM (NH4)2SO4 for 3h. Transcriptomic profiles were examined by microarray experiments. In all, 634 genes were up-regulated at least two-fold by the N-supplement when compared with expression in roots from untreated control plants. Gene Ontology (GO) enrichment analysis revealed that those upregulated genes are associated with 23 GO terms. Among them, metabolic processes for diverse amino acids (i.e., aspartate, threonine, tryptophan, glutamine, l-phenylalanine, and thiamin) as well as nitrogen compounds are highly over-represented, demonstrating that our selected genes are suitable for studying the N-response in roots. This enrichment analysis also indicated that nitrogen is closely linked to diverse transporter activities by primary metabolites, including proteins (amino acids), lipids, and carbohydrates, and is associated with carbohydrate catabolism and cell wall organization. Integration of results from omics analysis of metabolic pathways and transcriptome data using the MapMan tool suggested that the TCA cycle and pathway for mitochondrial electron transport are co-regulated when rice roots are exposed to ammonium. We also investigated the expression of N-responsive marker genes by performing a comparative analysis with root samples from plants grown under different NH4+ treatments. The diverse responses to such treatment provide useful insight into the global changes related to the shift from an N-deficiency to an enhanced N-supply in rice, a model crop plant.