Oryza Sativa Seedlings Research Articles

Regulation of ZnO nanoparticles-induced physiological and molecular changes by seed priming with humic acid in Oryza sativa seedlings

The present investigation explored the capability of priming treatment with 250 mg L−1 of humic acid (HA) to improve nano-ZnO tolerance of two rice cultivars seedlings (Zhu Liang You 06 and Qian You No. 1). The results showed that seed germination, seedling growth, total soluble protein, sugar and starch contents significantly improved by seed priming with HA especially under high nano-ZnO stress (500 and 750 mg L−1) as compared to unprimed seeds. In contrast, electrolyte leakage significantly increased after exposure to 500 and 750 mg L−1 nano-ZnO, but decreased obviously after HA priming in both cultivars. Abscisic acid (ABA) content in the seeds germinated under nano-ZnO stress was higher than those grown under non-stress condition; while gibberellins (GA) content decreased under nano-ZnO stress. HA priming down-regulated the relative expression levels of OsABA8ox2 and OsNCED1, which were key genes in ABA biosynthesis and catabolism of rice seeds. In contrast, up-regulation in OsGA20ox2 and OsGA3ox1 were induced by HA priming. The histochemical analysis reported that higher concentration of hydrogen peroxide (H2O2) and superoxide radical (O2·−) were observed in stressed roots with nano-ZnO as compared with non-stress condition, indicating reduction of root cell viability and severe oxidative burst. However, HA priming reduced obviously H2O2, O2·−, antioxidant enzymes activities (SOD, POD, CAT) and malondialdehyde (MDA) content of rice seedlings under stress. Significant increases in dehydroascorbate reductase (DHAR) and monodehydroascorbate reductase (MDAR) activities were observed in nano-ZnO stressed seedlings, but they were diminished evidently by HA priming. In addition, the improvement of HA on cell ultra structure of root tip and leaf mesophyll was detected under nano-ZnO stress especially 750 mg L−1 concentration. Therefore, it was suggested that HA priming could definitely improve the rice seed germination and seedling growth under nano-ZnO stress to some extent.

English

Environmental pollution from toxic heavy metals is a growing problem throughout the world due to the expansion of industrialisation. The use of microbes and biotechnological processes can provide alternative or complementary methods for the removal or recovery of heavy metals through bioremediation. The present study isolated, identified and characterised heavy metal-resistant fungi from cadmium- and chromium-contaminated paddy soil from Daye City, Hubei Province, China. Eight metal-resistant fungal species were obtained using an acclimation to concentration gradient approach. Five strains tolerated cadmium (Cd2+) to a maximum concentration of 16 mM, four strains could endure 1000 mg/L chromium (Cr2+), and Fusarium oxysporum could withstand high levels of both metals. Morphological examination and 18S rDNA sequence analysis identified the strains. Metal-resistant fungi were co-cultured with 5-day-old rice (Oryza sativa) seedlings in 1/2 MS medium for 7 days and growth parameters were compared with control rice not incubated with microbes. In the obtained strains, Metarhizium anisopliae had no influence on plant height or root length, and Saccharomyces cerevisiae had no effect on these parameters or on fresh weight. Heavy metal-resistant fungi such as those identified in this study could prove useful for the bioremediation of heavy metal-contaminated environments. Key words: Heavy metal resistance, co-cultivation, filamentous fungi, acclimation of concentration gradient, rice, bioremediation.

Detection and isolation of plant-associated bacteria scavenging atmospheric molecular hydrogen.

High-affinity hydrogen (H2 )-oxidizing bacteria possessing group 5 [NiFe]-hydrogenase genes are important contributors to atmospheric H2 uptake in soil environments. Although previous studies reported the occurrence of a significant H2 uptake activity in vegetation, there has been no report on the identification and diversity of the responsible microorganisms. Here, we show the existence of plant-associated bacteria with the ability to consume atmospheric H2 that may be a potential energy source required for their persistence in plants. Detection of the gene hhyL - encoding the large subunit of group 5 [NiFe]-hydrogenase - in plant tissues showed that plant-associated high-affinity H2 -oxidizing bacteria are widely distributed in herbaceous plants. Among a collection of 145 endophytic isolates, seven Streptomyces strains were shown to possess hhyL gene and exhibit high- or intermediate-affinity H2 uptake activity. Inoculation of Arabidopsis thaliana (thale cress) and Oryza sativa (rice) seedlings with selected isolates resulted in an internalization of the bacteria in plant tissues. H2 uptake activity per bacterial cells was comparable between plant and soil, demonstrating that both environments are favourable for the H2 uptake activity of streptomycetes. This study first demonstrated the occurrence of plant-associated high-affinity H2 -oxidizing bacteria and proposed their potential contribution as atmospheric H2 sink.

一个水稻铁转运基因(<italic>OsFRDL1</italic>)参与缺氧诱导根系铁膜形成的调节过程

Iron plaques that form on the surface of roots serve as an important nutrient reservoir and as a natural barrier for rice ( Oryza sativa ) seedlings to adapt to environmental stress. However, the molecular mechanism of iron plaque formation is poorly understood. In this study, the Osfrdl1 mutant and its wild-type (Nipponbare) cultivar were used to explore the role of the OsFRDL1 gene in iron plaque formation on rice roots. The results showed that a low phosphorus concentration ( Osfrdl1 mutant than on those of the wild-type. The results of real-time RT-PCR analyses indicated that the stagnant treatment increased the expression of OsFRDL1. As well, OsFRDL1 :: GUS staining indicated that the GUS reporter gene was mainly expressed in epidermis cells and stele tissues in the root. The expression of the reporter gene in these tissues was markedly higher in seedlings in the stagnant treatment than in those in the aerated treatment. In the stagnant treatment, the peroxidase activity was higher in roots of wild-type plants than in those of the Osfrdl1 mutant. Taken together, these results suggest that the stagnant treatment induced increased expression of OsFRDL1 . This increased the peroxidase activity to a higher level in the wild-type than in the mutant, and promoted greater iron plaque formation on the roots.

Photosynthesis mediated decrease in cadmium translocation protect shoot growth of Oryza sativa seedlings up on ammonium phosphate – sulfur fertilization

Cadmium (Cd) stress responses in seedlings of two Indian rice cultivars, MTU 7029 and MO 16 were investigated under ammonium-based fertilizer amendment. Cd translocation was reduced by fertilizer treatment. An increase in the production of organic acids as well as nitrogenous compounds and maintenance of nutrient status were implicated for decrease in Cd translocation which in turn promoted shoot growth. Fertilizer treatment increased photosynthetic pigments and activity of antioxidant enzymes that ensured steady photosynthetic rate during Cd stress. MO 16 showed Cd exclusion characteristics when compared with MTU 7029. Photosynthesis performance of MO 16 was not affected by Cd treatments. These findings suggest that photosynthesis influenced decrease in Cd translocation enhanced shoot growth of seedlings during ammonium phosphate-sulfur fertilizer supplementation.

Isolation,Partial Purification and Characterization of Phospholipid Hydroperoxide Glutathione Peroxidase(Phgpx Enzyme from Oryza Sativa Seedlings

The recombinant Phospholipid hydroperoxide glutathione peroxidase isolated from Oryza sativa is a type of antioxidant enzyme. It is stable at pH 7-8 and temperature 27 and 62°C. The molecular weight of enzyme was found to be around 21-26 kDa by SDS PAGE. The peroxidation activity of PHGPx was inhibited by HgCl2, EDTA, Potassium ferrocynate and was activated by FeCl2 and MnSO4 .These properties indicate that the possibilities for use of the PHGPx in the medical, clinical and cosmatic industry. This enzyme can be exploited commercially with some modification.

Differential expression of two fructokinases in Oryza sativa seedlings grown under aerobic and anaerobic conditions

Fructokinases (EC 2.7.1.4) may play an important role in carbohydrate metabolism of Oryza sativa L. (rice) seedlings under anoxia. We present here the molecular and biochemical characterizations of two rice fructokinases, namely OsFK1 and OsFK2. The results show that, at both a transcriptional and a transductional level, OsFK1 is preferentially expressed under aerobic conditions, whereas OsFK2 is induced under anoxia. Substrate inhibition was demonstrated for OsFK1, while OsFK2 appears to be largely unaffected by fructose concentrations up to 10 mM. Sugar modulation of anoxia-induced proteins has been proposed, but our results on rice calli treated with or without glucose (10, 30 or 90 mM) for different time indicate that neither OsFK1 nor OsFK2 are sugar-regulated. We propose that OsFK2 plays a major role in fructose phosphorylation under anoxic conditions.

Study of c is-cinnamic acid in Arabidopsis thaliana

Trans-cinnamic acid (CA) can be isomerized to cis-CA in Arabidopsis thaliana extract under sunlight. Piperonylic acid treatment of Arabidopsis under ultraviolet (UV) light increased the level of cis-CA in these treated tissues. Similarly, cis-CA was also detected from Oryza sativa seedlings grown under sunlight. These results suggest that cis-CA may occur in planta. Application of cis-CA to seedlings of both wild type Arabidopsis and auxin-insensitive mutants, aux1 and axr2, resulted in nearly identical dose response curves in root growth, indicating that the mode of action by which cis-CA affects plant growth is different from that of auxins. According to root growth inhibition assay, cis-CA is nearly 10 times more active than trans-CA. These results suggest that cis-CA is a unique plant growth regulator but its in vivo function remains to be elucidated.

On the Physiological Role of Anaerobically Synthesized Lipids in Oryza sativa Seedlings

The objective of this work was to elucidate a possible adaptive role of lipid biosynthesis and unsaturated fatty acids (FAs), esterified to lipids, as terminal acceptors of electrons, alternative to molecular oxygen, in the shoots of rice seedlings (Oryza sativa L.) under conditions of strict anoxia. Biosynthesis of lipids and their accumulation, as well as the reduction of double bonds in unsaturated FAs, were studied by electron microscopic observation of the accumulation of lipid bodies in the cytoplasm and by the biochemical analysis of FAs in shoot lipids before and after anaerobic incubation of the shoots. The experiments were carried out with intact coleoptiles after 5 and 8 days of anaerobic germination of seeds (primary anoxia) and with detached shoots, preliminarily grown in air and then subjected to anoxia in the presence of 2% glucose for 48 h (secondary anoxia). In these experiments, lipid bodies did not accumulate in the cytoplasm under anoxic conditions. Lipid bodies appeared only during 48-h anaerobic incubation of detached coleoptiles in the absence of exogenous glucose, when mitochondria degraded. There was no change either in the double bond index of FAs, or in the qualitative and quantitative composition of FAs during shoot anaerobic incubation. We conclude that neither lipids synthesized under anaerobic conditions nor esterified unsaturated FAs are involved in plant adaptation to anaerobiosis as terminal acceptors of electrons, alternative to molecular oxygen. Lipid biosynthesis under anoxic conditions, which was demonstrated for anoxia-tolerant seedlings of Oryza sativa and Echinochloa phyllopogon in experiments with radioactive precursors, 14C-acetate and 3H-glycerol, is only the manifestation of a turnover of saturated FAs and various classes of lipids, which stabilizes cell membranes under adverse conditions of strict anoxia.

Molecular cloning and characterization of a novel brassinolide enhanced gene OsBLE1 in Oryza sativa seedlings

Brassinosteroids (BRs) are plant steroids essential for normal growth and development. To gain insight into the molecular mechanism by which BRs regulate the growth and development of plants, it is necessary to identify and analyze more genes that are regulated by BRs. A novel brassinolide (BL)-enhanced gene designated OsBLE1, which was originally identified by using rice ( Oryza sativa L.) cDNA microarray, was cloned and characterized. Its cDNA is 598 bp long, encoding a predicted polypeptide with 81 amino acid residues. Northern blots analysis revealed that OsBLE1 expression began to increase at 6 h and reached its maximum at 12 h after BL treatment. OsBLE1 expression was most responsive to BL in lamina joint in rice seedlings; besides, IAA and GA 3 also enhanced its expression. OsBLE1 expressed mainly in active tissues such as vascular bundles and root primordial. Transgenic rice expressing antisense OsBLE1 exhibits various degrees of repressed growth. Results suggest that OsBLE1 might be involved in BL-regulated growth processes in rice seedlings.

Chitosan activates defense/stress response(s) in the leaves of Oryza sativa seedlings

In this study, we examined the response(s) of rice ( Oryza sativa L. japonica-type cv. Nipponbare) seedling leaves treated with a fungal elicitor chitosan (CT). Small brownish necrotic spots (streaks) appeared in the interveinal regions on the leaf surface after treatment by 0.1% CT, over the cut control. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblot analysis further revealed strong induction of ascorbate peroxidase, and changes in “phytocystatins” (cysteine proteinase inhibitors). Using two-dimensional polyacrylamide gel electrophoresis, evidence is provided for the accumulation of two major classes of pathogenesis-related (PR) proteins, namely OsPR5 and OsPR10 in the leaves. In parallel, northern analyses revealed potent accumulation of the OsPR5 and OsPR10 mRNAs; a time- and dose-dependent expression, and a requirement for de novo protein synthesis was observed. Furthermore, CT-elicited changes were also accompanied by production of anti-fungal phytoalexins, the flavonoid sakuranetin and the diterpenoid lactone momilactone A, as determined by liquid chromatography-mass spectrometry/mass spectrometry analysis. Present results reveal for the first time the potency of CT in initiating multiple events linked with defense/stress response(s) in the leaves of whole rice plants.

Growth inhibitory effects of nutgrass (Cyperus rotundus) on rice (Oryza sativa) seedlings.

Growth inhibitory effects of aqueous extracts and leachates of leaves and tubers of Cyperus rotundus L. were investigated by using rice (Oryza sativa L.) seedling as a bioassay material. Both the extracts and leachates of Cyperus were inhibitory to the growth of rice seedlings. Growth inhibition was more pronounced in the presence of aqueous extracts than the leachates. The extract and leachate of leaves had higher total phenolic contents than those of the tubers. Soil amendment with fresh leaves of Cyperus reduced plant height, leaf area, and root and shoot weight of rice seedlings. Total phenolic content was higher in soil amended with fresh Cyperus leaves than the unamended control soil. Nineteen compounds were tentatively identified from the aqueous extracts of leaves and tubers by ethyl acetate extraction followed by gas chromatography–mass spectroscopy (GC-MS). Dicarboxylic, phenolic, and fatty acids were the major compounds. Our results suggest that Cyperus may affect the growth and establishment of rice seedlings after sowing or transplanting, especially when Cyperus plants are mixed in soil during land preparation by ploughing in rain-fed rice culture.

Cloning and characterization of a cDNA encoding gibberellin 20-oxidase from rice (Oryza sativa) seedlings

Cloning and characterization of a cDNA encoding gibberellin 20-oxidase from rice (Oryza sativa) seedlings

A synopsis of the occurrence and pathogenicity of Phytophthora species in mainland China.

To date, 26 species of Phytophthora have been reported in mainland China but only 23 are accepted as good taxa. Phytophthora nicotianae (P. parasitica) is the single most important species causing over 40 different plant diseases; P. boehmeriae is widespread attacking Gossypium, Boehmeria, Citrus, Broussonetia papyrifera and Pterocarya stenoptera; P. "fragariae var. oryzo-bladis" is unique to mainland China causing blight of Oryza sativa seedlings; P. megasperma sensu lato has been isolated from Glycine max, Asparagus officinalis and Spinacia oleracea. In Hainan Province, P. heveae is present in the soil without causing apparent diseases to Hevea brasiliensis there.

Localization of acid phosphatases in root cap of rice plant

Acid phosphatases are widely distributed in different tisssues of various plants. Studies on subcellular localization of acid phosphatases show they might be present in cell wall, plasma lemma, mitochondria, plastid, vacuole and nucleus. However, their localization in rice cell varies with developmental stages of cells and plant tissues. In present study, acid phosphatases occurring in root cap are examined.Sliced root tips of ten-day-old rice(Oryza sativa)seedlings were fixed in 0.1M cacodylate buffer containing 2.5% glutaraldehyde for 2h, washed overnight in same buffer solution, incubated in Gomori's solution at 37° C for 90min, post-fixed in OsO4, dehydrated in ethanol series and finally embeded in Spurr's resin. Sections were doubly stained with uranyl acetate and lead citrate, and observed under Hitachi H-600 at 75 KV.

A novel ras-related rgp1 gene encoding a GTP-binding protein has reduced expression in 5-azacytidine-induced dwarf rice

Exposure of normal, tall rice (Oryza sativa) seedlings to 5-azacytidine, a powerful inhibitor of DNA methylation in vivo, induced both demethylation of genomic DNA and dwarf plants. Genes that had been affected by treatment were identified by differential screening of a cDNA library, and a ras-related gene, rgp1, was subsequently isolated. The cDNA of rgp1 was found to encode a deduced protein sequence of 226 amino acids with a relative molecular mass of 24850, which was most closely related to the ras-related ypt3 protein of fission yeast, Schizosaccharomyces pombe. The rgp1 protein, expressed in transformed Escherichia coli, clearly showed GTP-binding activity. During seedling rgp1 expression was first observed 14 days after germination, reaching a maximum level between 28 and 42 days, and gradually decreased thereafter until 63 days when it attained the same level of expression as in 14-day-old seedlings. Expression of rgp1 was found to be markedly reduced throughout the growth period of both 5-azacytidine-induced dwarf plants and their progenies, relative to levels in untreated tall control plants. These results suggest that expression of rgp1 may be influenced, either directly or indirectly, by DNA methylation, and that the rgp1 protein may play an important role in plant growth and development.

Asparagine biosynthesis by Oryza sativa seedlings

l-Aspartate-[U- 14C] was quickly metabolized in rice seedlings into amino acids, organic acids and sugars. On feeding simultaneously with ammonium for 2 hr, about 1% of the total soluble radioactivity was recovered as asparagine. Major amino acids labelled were aspartate, glutamate, glutamine and alanine in both shoots and roots. On the other hand, on feeding l-aspartate-[U- 14C] to rice seedlings precultured in an ammonium medium, asparagine accounted for 35% of the total soluble radioactivity in the roots. Different labelling patterns in amino acids from those of non-precultured tissues were observed, and the main amino acids labelled in this case were asparagine and γ-aminobutyrate in the roots; glutamate, asparagine and glutamine in the shoots. It was observed in the roots that this increase of asparagine labelling was associated with a decrease of label in glutamate.