Removal of ammonium and manganese from surface water using a MeOx filter system as a pretreatment process.

Residual aluminium from the coagulation-sedimentation process in the treatment of surface water can decrease the catalytic activity of a manganese co-oxide filter film (MeOx) used for ammonium and manganese removal. To solve this problem, a MeOx filter was used as a pretreatment process to filtrate source water directly before the coagulation and sedimentation treatment. The removal performance and the mechanism of change in the activity of MeOx were investigated. The experimental results indicated that the MeOx filter removed ammonium and manganese from surface water sources effectively, and its manganese removal activity was enhanced. The characteristics of MeOx were investigated via SEM, EDS, XPS, and the BET surface area. Analysis of the experimental results showed that the increase in the content of Al under this condition was much lower than that under treatment with the coagulation-sedimentation process. After long-term operation, the amount and surface area of MeOx coated on the filter sand increased significantly, leading to an increase in the catalytic activity. However, in cold water, the catalytic activity of MeOx decreased, and more Mn(II) was obtained on the surface of MeOx. Thus, the morphology of MeOx changed. Fortunately, when water temperature increases, the removal activity can recover immediately. By inactivating microorganisms and comparing the removal performance with that under other conditions, the MeOx activity of the pretreatment process is preserved effectively and no strengthening measures are required. This study will provide a new strategy for the use of the MeOx catalytic technology.

Full-Scale Experimental Study of Groundwater Softening in a Circulating Pellet Fluidized Reactor.

The softening effect of a new type of circulating pellet fluidized bed (CPFB) reactor on groundwater was studied through a full-scale experiment. The operation of the CPFB reactor in the second water plant in Chang'an District in Xi'an China was monitored for one year, and the results were compared with those for the Amsterdam reactor in The Netherlands. The removal efficiency of Ca2+ in the CPFB reactor reached 90%; the removal rate of total hardness was higher than 60%; effluent pH was 9.5⁻9.8; the turbidity of the effluent and the turbidity after boiling were lower than 1.0 NTU; the unit cost was less than €0.064 per m³; and the softened effluent was stable. The pellets in the CPFB reactor were circulated, providing higher crystallization efficiency. The diameter of the discharged pellets reached between 3⁻5 mm, and the fluidized area height of the CPFB reactor was 4 m. The performance parameters of the CFPB reactor were optimized.

Identification of a residue in helix 2 of rice plasma membrane intrinsic proteins that influences water permeability.

Molecular selection, ion exclusion, and water permeation are well known regulatory mechanisms in aquaporin. Water permeability was found to be diverse in different subgroups of plasma membrane intrinsic proteins (PIPs), even though the residues surrounding the water holes remained the same across the subgroups. Upon homology modeling and structural comparison, a conserved Ala/Ile(Val) residue difference was identified in helix 2 that affected the conformation of the NPA region and consequently influenced the water permeability. The residue difference was found to be conservative within the two subgroups of PIPs in rice as well as in other plants. Functional tests further confirmed the prediction via site-directed mutagenesis where replacement of Ala(103) or Ala(102) in respective OsPIP1;1 or OsPIP1;3 with Val yielded 7.0- and 2.2-fold increases in water transportation, and substitution of Ile(98) or Val(95) in respective OsPIP2;3 or OsPIP2;7 with Ala resulted in 73 or 52% reduction of water transportation. Based on structural analyses and molecular dynamics simulations, we proposed that the difference in water permeability was attributed to the orientation variations of helix 2 that modified water-water and water-protein interactions.

Proteomic study of Carissa spinarum in response to combined heat and drought stress.

Carissa spinarum is one of the secondary advantage plants grown in dry-hot valleys in China, which can survive under stress conditions of high temperature and extreme low humidity. Here, we studied the physiological and proteomic changes of C. spinarum in response to 42 degrees C heat stress treatment in combination with drought stress. Dynamic changes in the leaf proteome were analyzed at four time points during the stress treatment and recovery stages. Approximately, 650 protein spots were reproducibly detected in each gel. Forty-nine spots changed their expression levels upon heat and drought treatment, and 30 proteins were identified by MS and 2-D Western blot. These proteins were classified into several categories including HSP, photosynthesis-related protein, RNA-processing protein and proteins involved in metabolism and energy production. The potential roles of these stress-responsive proteins are discussed.

The role of water channel proteins and nitric oxide signaling in rice seed germination.

Previous studies have demonstrated the possible role of several aquaporins in seed germination. But systematic investigation of the role of aquaporin family members in this process is lacking. Here, the developmental regulation of plasma membrane intrinsic protein (PIP) expression throughout germination and post-germination processes in rice embryos was analyzed. The expression patterns of the PIPs suggest these aquaporins play different roles in seed germination and seedling growth. Partial silencing of the water channel genes, OsPIP1;1 and OsPIP1;3, reduced seed germination while over-expression of OsPIP1;3 promoted seed germination under water-stress conditions. Moreover, spatial expression analysis indicates that OsPIP1;3 is expressed predominantly in embryo during seed germination. Our data also revealed that the nitric oxide (NO) donors, sodium nitroprusside (SNP) and S-nitrosoglutathione (GSNO), promoted seed germination; furthermore, the NO scavenger, 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, inhibited germination and reduced the stimulative effects of SNP and GSNO on rice germination. Exogenous NO stimulated the transcription of OsPIP1;1, OsPIP1;2, OsPIP1;3 and OsPIP2;8 in germinating seeds. These results suggest that water channels play an important role in seed germination, acting, at least partly, in response to the NO signaling pathway.

Isolation and functional characterization of PgTIP1, a hormone-autotrophic cells-specific tonoplast aquaporin in ginseng.

The suppression subtractive hybridization technique was used to identify differentially expressed genes between hormone-autotrophic and hormone-dependent Panax ginseng callus lines. A tonoplast intrinsic protein cDNA (PgTIP1) was found to be highly and specifically expressed in hormone-autotrophic ginseng cells, which was slightly up-regulated by cytokinin while significantly down-regulated when treated with auxin. PgTIP1 encodes a polypeptide of 250 amino acids which shows sequence and structure similarity with tonoplast aquaporins in plants. The water channel activity of PgTIP1 was demonstrated by its expression in Xenopus laevis oocytes. When over-expressed in Arabidopsis thaliana, PgTIP1 substantially altered the plant's vegetative and reproductive growth and development. Arabidopsis plants over-expressing PgTIP1 showed significantly enhanced seed size and seed mass plus greatly increased growth rate compared with those of the wild type. Moreover, the seeds from PgTIP1 over-expressing Arabidopsis had 1.85-fold higher fatty acid content than the wild-type control. These results demonstrate a significant function of PgTIP1 in the growth and development of plant cells.

Upland rice and lowland rice exhibited different PIP expression under water deficit and ABA treatment.

Aquaporins play a significant role in plant water relations. To further understand the aquaporin function in plants under water stress, the expression of a subgroup of aquaporins, plasma membrane intrinsic proteins (PIPs), was studied at both the protein and mRNA level in upland rice (Oryza sativa L. cv. Zhonghan 3) and lowland rice (Oryza sativa L. cv. Xiushui 63) when they were water stressed by treatment with 20% polyethylene glycol (PEG). Plants responded differently to 20% PEG treatment. Leaf water content of upland rice leaves was reduced rapidly. PIP protein level increased markedly in roots of both types, but only in leaves of upland rice after 10 h of PEG treatment. At the mRNA level, OsPIP1;2, OsPIP1;3, OsPIP2;1 and OsPIP2;5 in roots as well as OsPIP1;2 and OsPIP1;3 in leaves were significantly up-regulated in upland rice, whereas the corresponding genes remained unchanged or down-regulated in lowland rice. Meanwhile, we observed a significant increase in the endogenous abscisic acid (ABA) level in upland rice but not in lowland rice under water deficit. Treatment with 60 microM ABA enhanced the expression of OsPIP1;2, OsPIP2;5 and OsPIP2;6 in roots and OsPIP1;2, OsPIP2;4 and OsPIP2;6 in leaves of upland rice. The responsiveness of PIP genes to water stress and ABA were different, implying that the regulation of PIP genes involves both ABA-dependent and ABA-independent signaling pathways during water deficit.

Comparative proteomic analysis provides new insights into chilling stress responses in rice.

Low temperature is one of the major abiotic stresses limiting the productivity and the geographical distribution of many important crops. To gain a better understanding of chilling stress responses in rice (Oryza sativa L. cv. Nipponbare), we carried out a comparative proteomic analysis. Three-week-old rice seedlings were treated at 6 degrees C for 6 or 24 h and then recovered for 24 h. Chilling treatment resulted in stress phenotypes of rolling leaves, increased relative electrolyte leakage, and decreased net photosynthetic rate. The temporal changes of total proteins in rice leaves were examined using two-dimensional electrophoresis. Among approximately 1,000 protein spots reproducibly detected on each gel, 31 protein spots were down-regulated, and 65 were up-regulated at least at one time point. Mass spectrometry analysis allowed the identification of 85 differentially expressed proteins, including well known and novel cold-responsive proteins. Several proteins showed enhanced degradation during chilling stress, especially the photosynthetic proteins such as Rubisco large subunit of which 19 fragments were detected. The identified proteins are involved in several processes, i.e. signal transduction, RNA processing, translation, protein processing, redox homeostasis, photosynthesis, photorespiration, and metabolisms of carbon, nitrogen, sulfur, and energy. Gene expression analysis of 44 different proteins by quantitative real time PCR showed that the mRNA level was not correlated well with the protein level. In conclusion, our study provides new insights into chilling stress responses in rice and demonstrates the advantages of proteomic analysis.

Gibberellin-regulated XET is differentially induced by auxin in rice leaf sheath bases during gravitropic bending.

The asymmetric distribution of auxin plays a fundamental role in plant gravitropism, yet little is understood about how its lateral distribution stimulates growth. In the present work, the asymmetric distribution not only of auxin, but also that of gibberellins (GAs), was observed in rice leaf sheath bases following gravistimulation. Gravistimulation induced the transient accumulation of greater amounts of both IAA and GA in the lower halves of the leaf sheath bases of rice seedlings. OsGA3ox1, a gene of active GA synthesis, was differentially induced by gravistimulation. Furthermore, 2,3,5-tri-iodobenzoic acid (TIBA), an inhibitor of auxin transport, substantially decreased the asymmetric distribution of IAA and the gradient of OsGA3ox1 expression. Externally applied GA(3) restored the gravitropic curvature of rice leaf sheaths inhibited by either TIBA or by ancymidol, a GA synthesis inhibitor. The expression of XET (encoding xyloglucan endotransglycosylase) was differentially induced in the lower halves of gravistimulated leaf sheath bases and was also up-regulated by exogenous IAA and GA(3). Both ancymidol and TIBA decreased the gradient of XET expression. These data suggest that the asymmetric distribution of auxin effected by gravistimulation induced a gradient of GAs via asymmetric expression of OsGA3ox1 in rice leaf sheath bases, and hence caused the asymmetric expression of XET. Cell wall loosening in the curvature site of the leaf sheath triggered by the expression of XET would contribute to gravitropic growth.

Nitric oxide mediates gravitropic bending in soybean roots.

Plant roots are gravitropic, detecting and responding to changes in orientation via differential growth that results in bending and reestablishment of downward growth. Recent data support the basics of the Cholodny-Went hypothesis, indicating that differential growth is due to redistribution of auxin to the lower sides of gravistimulated roots, but little is known regarding the molecular details of such effects. Here, we investigate auxin and gravity signal transduction by demonstrating that the endogenous signaling molecules nitric oxide (NO) and cGMP mediate responses to gravistimulation in primary roots of soybean (Glycine max). Horizontal orientation of soybean roots caused the accumulation of both NO and cGMP in the primary root tip. Fluorescence confocal microcopy revealed that the accumulation of NO was asymmetric, with NO concentrating in the lower side of the root. Removal of NO with an NO scavenger or inhibition of NO synthesis via NO synthase inhibitors or an inhibitor of nitrate reductase reduced both NO accumulation and gravitropic bending, indicating that NO synthesis was required for the gravitropic responses and that both NO synthase and nitrate reductase may contribute to the synthesis of the NO required. Auxin induced NO accumulation in root protoplasts and asymmetric NO accumulation in root tips. Gravistimulation, NO, and auxin also induced the accumulation of cGMP, a response inhibited by removal of NO or by inhibitors of guanylyl cyclase, compounds that also reduced gravitropic bending. Asymmetric NO accumulation and gravitropic bending were both inhibited by an auxin transport inhibitor, and the inhibition of bending was overcome by treatment with NO or 8-bromo-cGMP, a cell-permeable analog of cGMP. These data indicate that auxin-induced NO and cGMP mediate gravitropic curvature in soybean roots.

Proteomic analysis of salt stress-responsive proteins in rice root.

Salt stress is one of the major abiotic stresses in agriculture worldwide. We report here a systematic proteomic approach to investigate the salt stress-responsive proteins in rice (Oryza sativa L. cv. Nipponbare). Three-week-old seedlings were treated with 150 mM NaCl for 24, 48 and 72 h. Total proteins of roots were extracted and separated by two-dimensional gel electrophoresis. More than 1100 protein spots were reproducibly detected, including 34 that were up-regulated and 20 down-regulated. Mass spectrometry analysis and database searching helped us to identify 12 spots representing 10 different proteins. Three spots were identified as the same protein, enolase. While four of them were previously confirmed as salt stress-responsive proteins, six are novel ones, i.e. UDP-glucose pyrophosphorylase, cytochrome c oxidase subunit 6b-1, glutamine synthetase root isozyme, putative nascent polypeptide associated complex alpha chain, putative splicing factor-like protein and putative actin-binding protein. These proteins are involved in regulation of carbohydrate, nitrogen and energy metabolism, reactive oxygen species scavenging, mRNA and protein processing, and cytoskeleton stability. This study gives new insights into salt stress response in rice roots and demonstrates the power of the proteomic approach in plant biology studies.

Mitogen-activated protein kinases mediate the oxidative burst and saponin synthesis induced by chitosan in cell cultures of Panax ginseng.

Chitosan (CHN) specially induced the activities of 39 kD and 42 kD protein kinases in ginseng cells, which could be suppressed by an inhibitor of mitogen-activated protein kinase (MAPK) pathway, PD98059. The immunoprecipitation (IP) using MAPK antibody or kinase assay in vitro also showed that CHN-induced 42 kD and 39 kD protein kinases belonged to the MAPK family. PD98059 suppressed CHN-induced transcriptions of ginseng squalene synthase and ginseng squalene epoxidase genes (gss and gse), CHN-induced accumulation of beta-Amyrin synthase (beta-AS) and synthesis of saponin. These results showed that CHN-induced activities of MAPKs were necessary for the CHN-induced saponin synthesis. EGTA and LaCl3 suppressed CHN-induced 39 kD and 42 kD MAPK activities. Ruthenium red (RR) could suppress CHN-induced 39 kD activity. All of them suppressed CHN-induced saponin synthesis. These results indicated that CHN-induced increment of cytosolic calcium was necessary for CHN-induced saponin synthesis. PD98059 also suppressed CHN-induced oxidative burst (including the increment of activity of plasma membrane NADPH oxidase and production of H2O2), but diphenylene iodonium (DPI), dimethylthiourea (DMTU) and 2,5-dihydroxycinnamic acid methyl ester (DHC) could not suppress CHN-induced MAPK activities, which indicated that MAPK was possibly function upstream of CHN-induced oxidative burst.

The role of aquaporin RWC3 in drought avoidance in rice.

Although the discovery of aquaporins in plants has resulted in a paradigm shift in the understanding of plant water relations, the relationship between aquaporins and drought resistance still remains elusive. From an agronomic viewpoint, upland rice is traditionally considered as showing drought avoidance. In the investigation of different morphological and physiological responses of upland rice (Oryza sativa L. spp indica cv. Zhonghan 3) and lowland rice (O. sativa L. spp japonica cv. Xiushui 63) to water deficit, we observed young leaf rolling and the remarkable decline of cumulative transpiration in the upland rice. The expression of water channel protein RWC3 mRNA was increased in upland rice at the early response (up to 4 h) to the 20% polyethylene glycol (PEG) 6000 treatment, whereas there was no significant expression changes in lowland rice. Protein levels were increased in upland rice and decreased in lowland rice at 10 h after the water deficit. The up-regulation of RWC3 in upland rice fits well with the knowledge that upland rice adopts the mechanism of drought avoidance. The physiological significance of this RWC3 up-regulation was then explored with the over-expression of RWC3 in transgenic lowland rice (O. sativa L. spp japonica cv. Zhonghua 11) controlled by a stress-inducible SWPA2 promoter. Compared to the wild-type plant, the transgenic lowland rice exhibited higher root osmotic hydraulic conductivity (Lp), leaf water potential and relative cumulative transpiration at the end of 10 h PEG treatment. These results indicated that RWC3 probably played a role in drought avoidance in rice.

Alkali grass resists salt stress through high [K+] and an endodermis barrier to Na+.

In order to understand the salt-tolerance mechanism of alkali grass (Puccinellia tenuiflora) compared with wheat (Triticum aestivum L.), [K(+)] and [Na(+)] in roots and shoots in response to salt treatments were examined with ion element analysis and X-ray microanalysis. Both the rapid K(+) and Na(+) influx in response to different NaCl and KCl treatments, and the accumulation of K(+) and Na(+) as the plants acclimated to long-term stress were studied in culture- solution experiments. A higher K(+) uptake under normal and saline conditions was evident in alkali grass compared with that in wheat, and electrophysiological analyses indicated that the different uptake probably resulted from the higher K(+)/Na(+) selectivity of the plasma membrane. When external [K(+)] was high, K(+) uptake and transport from roots to shoots were inhibited by exogenous Cs(+), while TEA (tetraethylammonium) only inhibited K(+) transport from the root to the shoot. K(+) uptake was not influenced by Cs(+) when plants were K(+) starved. It was shown by X-ray microanalysis that high [K(+)] and low [Na(+)] existed in the endodermal cells of alkali grass roots, suggesting this to be the tissue where Cs(+) inhibition occurs. These results suggest that the K(+)/Na(+) selectivity of potassium channels and the existence of an apoplastic barrier, the Casparian bands of the endodermis, lead to the lateral gradient of K(+) and Na(+) across root tissue, resulting not only in high levels of [K(+)] in the shoot but also a large [Na(+)] gradient between the root and the shoot.

Nitric oxide mediates elicitor-induced saponin synthesis in cell cultures of Panax ginseng.

The elicitor oligogalacturonic acid (OGA) stimulated nitric oxide (NO) accumulation in the growth medium of ginseng suspension cultures and induced increased nitric oxide synthase (NOS) activity in ginseng cells. OGA also stimulated accumulation of saponin, transcription of genes encoding squalene synthase (sqs) and squalene epoxidase (sqe), two early enzymes of saponin synthesis, and the accumulation of ß-amyrin synthase protein (ß-AS). Saponin accumulation, sqs and sqe gene expression, and increases in ß-AS content were also induced by exposure to NO via the NO donor sodium nitroprusside (SNP). Inhibitors of mammalian nitric oxide synthase reduced both OGA-induced NO accumulation and NOS activity, suggesting that OGA-induced NO production occurs via a NOS-like enzyme. OGA-induced accumulation of ß-AS and saponin, and transcription of sqs and sqe, were suppressed by treatments that removed NO or inhibited its production, indicating a role for NO in mediating OGA effects on these defence responses. NO accumulation and increased NOS activity were inhibited by calcium channel inhibitors and a protein kinase inhibitor, but not by a protein phosphatase inhibitor, indicating the requirement for calcium and protein phosphorylation during OGA-induced NO production. Saponin production and transcription, and accumulation of saponin biosynthetic genes and enzymes were also suppressed by these treatments, as well as by the protein phosphatase inhibitor okadaic acid.