The organization of high-affinity ammonium uptake in Arabidopsis roots depends on the spatial arrangement and biochemical properties of AMT1-type transporters

The AMMONIUM TRANSPORTER (AMT) family comprises six isoforms in Arabidopsis thaliana. Here, we describe the complete functional organization of root-expressed AMTs for high-affinity ammonium uptake. High-affinity influx of (15)N-labeled ammonium in two transposon-tagged amt1;2 lines was reduced by 18 to 26% compared with wild-type plants. Enrichment of the AMT1;2 protein in the plasma membrane and localization of AMT1;2 promoter activity in the endodermis and root cortex indicated that AMT1;2 mediates the uptake of ammonium entering the root via the apoplasmic transport route. An amt1;1 amt1;2 amt1;3 amt2;1 quadruple mutant (qko) showed severe growth depression under ammonium supply and maintained only 5 to 10% of wild-type high-affinity ammonium uptake capacity. Transcriptional upregulation of AMT1;5 in nitrogen-deficient rhizodermal and root hair cells and the ability of AMT1;5 to transport ammonium in yeast suggested that AMT1;5 accounts for the remaining uptake capacity in qko. Triple and quadruple amt insertion lines revealed in vivo ammonium substrate affinities of 50, 234, 61, and 4.5 muM for AMT1;1, AMT1;2, AMT1;3, and AMT1;5, respectively, but no ammonium influx activity for AMT2;1. These data suggest that two principle means of achieving effective ammonium uptake in Arabidopsis roots are the spatial arrangement of AMT1-type ammonium transporters and the distribution of their transport capacities at different substrate affinities.

Additive contribution of AMT1;1 and AMT1;3 to high-affinity ammonium uptake across the plasma membrane of nitrogen-deficient Arabidopsis roots

In Arabidopsis four root-expressed AMT genes encode functional ammonium transporters, which raises the question of their role in primary ammonium uptake. After pre-culturing under nitrogen-deficiency conditions, we quantified the influx of (15)N-labeled ammonium in T-DNA insertion lines and observed that the loss of either AMT1;1 or AMT1;3 led to a decrease in the high-affinity ammonium influx of approximately 30%. Under nitrogen-sufficient conditions the ammonium influx was lower in Columbia glabra compared with Wassilewskija (WS), and AMT1;1 did not contribute significantly to the ammonium influx in Col-gl. Ectopic expression of AMT1;3 under the control of a 35S promoter in either of the insertion lines amt1;3-1 or amt1;1-1 increased the ammonium influx above the level of their corresponding wild types. In transgenic lines carrying AMT-promoter-GFP constructs, the promoter activities of AMT1;1 and AMT1;3 were both upregulated under nitrogen-deficiency conditions and were localized to the rhizodermis, including root hairs. AMT gene-GFP fusions that were stably expressed under the control of their own promoters were localized to the plasma membrane. The double insertion line amt1;1-1amt1;3-1 showed a decreased sensitivity to the toxic ammonium analog methylammonium and a decrease in the ammonium influx of up to 70% relative to wild-type plants. These results suggest an additive contribution of AMT1;1 and AMT1;3 to the overall ammonium uptake capacity in Arabidopsis roots under nitrogen-deficiency conditions.

Reduced-intensity unrelated cord blood transplantation for treatment of metastatic renal cell carcinoma: first evidence of cord-blood-versus-solid-tumor effect

We report a 69-year-old man with cytokine-resistant metastatic renal cell carcinoma treated with reduced-intensity unrelated cord blood transplantation. The patient achieved durable donor engraftment with minimal graft-versus-host disease. The patient showed regression of metastatic disease, providing the first evidence of a graft-versus-tumor effect on a solid tumor resulting from cord blood graft.

Gln49 and Ser174 residues play critical roles in determining the catalytic efficiencies of plant glutamine synthetase

Two essential residues playing critical roles in determining the substrate specificities of cytosolic glutamine synthetase (GS1) have been identified from the alignment of high-affinity (GLN1;1 and GLN1;4) and low-affinity (GLN1;2 and GLN1;3) GS1 isoenzymes in Arabidopsis, and confirmed by site-directed mutagenesis. The results indicated that either K49Q or A174S mutation is sufficient to increase the catalytic efficiencies of GLN1;3 by decreasing its Km values for ammonium. In contrast, replacement of Gln49 and Ser174 by lysine and alanine, respectively, was detrimental to glutamine synthetic activities in GLN1;4. The results suggested that Gln49 and Ser174 in the high-affinity GS1 isoenzymes are interchangeable with Lys49 and Ala174 in the low-affinity variants at the corresponding positions.

Differential distribution of proteins expressed in companion cells in the sieve element-companion cell complex of rice plants

Sieve tubes are comprised of sieve elements, enucleated cells that are incapable of RNA and protein synthesis. The proteins in sieve elements are supplied from the neighboring companion cells through plasmodesmata. In rice plants, it was unclear whether or not all proteins produced in companion cells had the same distribution pattern in the sieve element-companion cell complex. In this study, the distribution pattern of four proteins, beta-glucuronidase (GUS), green fluorescent protein (GFP), thioredoxin h (TRXh) and glutathione S-transferase (GST) were analyzed. The foreign proteins GUS and GFP were expressed in transgenic rice plants under the control of the TRXh gene promoter (PTRXh), a companion cell-specific promoter. Analysis of leaf cross-sections of PTRXh-GUS and PTRXh-GFP plants indicated high accumulation of GUS and GFP, respectively, in companion cells rather than in sieve elements. GUS and GFP were also detected in phloem sap collected from leaf sheaths of the transgenic rice plants, suggesting these proteins could enter sieve elements. Relative amounts of GFP and endogenous phloem proteins, TRXh and GST, in phloem sap and total leaf extracts were compared. Compared to TRXh and GST, GFP content was higher in total leaf extracts, but lower in phloem sap, suggesting that GFP accumulated mainly in companion cells rather than in sieve elements. On the other hand, TRXh and GST appeared to accumulate in sieve elements rather than in companion cells. These results indicate the evidence for differential distribution of proteins between sieve elements and companion cells in rice plants.

Overexpression of AtCpNifS enhances selenium tolerance and accumulation in Arabidopsis

Selenium (Se) is an essential element for many organisms but is toxic at higher levels. CpNifS is a chloroplastic NifS-like protein in Arabidopsis (Arabidopsis thaliana) that can catalyze the conversion of cysteine into alanine and elemental sulfur (S0) and of selenocysteine into alanine and elemental Se (Se0). We overexpressed CpNifS to investigate the effects on Se metabolism in plants. CpNifS overexpression significantly enhanced selenate tolerance (1.9-fold) and Se accumulation (2.2-fold). CpNifS overexpressors showed significantly reduced Se incorporation into protein, which may explain their higher Se tolerance. Also, sulfur accumulation was enhanced by approximately 30% in CpNifS overexpressors, both on media with and without selenate. Root transcriptome changes in response to selenate mimicked the effects observed under sulfur starvation. There were only a few transcriptome differences between CpNifS-overexpressing plants and wild type, besides the 25- to 40-fold increase in CpNifS levels. Judged from x-ray analysis of near edge spectrum, both CpNifS overexpressors and wild type accumulated mostly selenate (Se(VI)). In conclusion, overexpression of this plant NifS-like protein had a pronounced effect on plant Se metabolism. The observed enhanced Se accumulation and tolerance of CpNifS overexpressors show promise for use in phytoremediation.

Severe reduction in growth rate and grain filling of rice mutants lacking OsGS1;1, a cytosolic glutamine synthetase1;1

Rice (Oryza sativa L.) plants possess three homologous but distinct genes for cytosolic glutamine synthetase (GS1): these are OsGS1;1, OsGS1;2, and OsGS1;3. OsGS1;1 was expressed in all organs tested with higher expression in leaf blades, while OsGS1;2, and OsGS1;3 were expressed mainly in roots and spikelets, respectively. We characterized knockout mutants caused by insertion of endogenous retrotransposon Tos17 into the exon-8 (lines ND8037 and ND9801) or the exon-10 (line NC2327) of OsGS1;1. Mendelian segregation occurred in each progeny. Homozygously inserted mutants showed severe retardation in growth rate and grain filling when grown at normal nitrogen concentrations. Abnormal mRNA for GS1;1 was transcribed, and the GS1 protein and its activity in the leaf blades were barely detectable in these mutants. The glutamine pool in the roots and leaf blades of the mutants was lower than that of the wild type. Re-introduction of OsGS1;1 cDNA under the control of its own promoter into the mutants successfully complemented these phenotypes. Progeny where Tos17 was heterozygously inserted or deleted during segregation showed normal phenotypes. The results indicate that GS1;1 is important for normal growth and grain filling in rice; GS1;2 and GS1;3 were not able to compensate for GS1;1 function.

Biochemical background and compartmentalized functions of cytosolic glutamine synthetase for active ammonium assimilation in rice roots

Rice plants in paddy fields prefer to utilize ammonium as a major nitrogen source. Glutamine synthetase (GS) serves for assimilation of ammonium in rice root, and ameliorates the toxic effect of ammonium excess. Among the three isoenzymes of the cytosolic GS1 gene family in rice, OsGLN1;1 and OsGLN1;2 were abundantly expressed in roots. Analysis of the purified enzymes showed that OsGLN1;1 and OsGLN1;2 can be classified into high-affinity subtypes with relatively high V(max) values, as compared with the major high-affinity isoenzyme, GLN1;1, in Arabidopsis. Low-affinity forms of GS1 comparable to those in Arabidopsis (GLN1;2 and GLN1;3) were absent in rice roots. The OsGLN1;1 and OsGLN1;2 transcripts showed reciprocal responses to ammonium supply in the surface cell layers of roots. OsGLN1;1 accumulated in dermatogen, epidermis and exodermis under nitrogen-limited condition. By contrast, OsGLN1;2 was abundantly expressed in the same cell layers under nitrogen-sufficient conditions, replenishing the loss of OsGLN1;1 following ammonium treatment. Within the central cylinder of elongating zone, OsGLN1;1 and OsGLN1;2 were both induced by ammonium, which was distinguishable from the response observed in the surface cell layers. The high-capacity Gln synthetic activities of OsGLN1;1 and OsGLN1;2 facilitate active ammonium assimilation in specific cell types in rice roots.

Kinetic properties and ammonium-dependent regulation of cytosolic isoenzymes of glutamine synthetase in Arabidopsis

Glutamine synthetase (GS; EC 6.3.1.2) is a key enzyme of nitrogen assimilation, catalyzing the synthesis of glutamine from ammonium and glutamate. In Arabidopsis, cytosolic GS (GS1) was accumulated in roots when plants were excessively supplied with ammonium; however, the GS activity was controlled at a constant level. The discrepancy between the protein content and enzyme activity of GS1 was attributable to the kinetic properties and expression of four distinct isoenzymes encoded by GLN1;1, GLN1;2, GLN1;3 and GLN1;4, genes that function complementary to each other in Arabidopsis roots. GLN1;2 was the only isoenzyme significantly up-regulated by ammonium, which correlated with the rapid increase in total GS1 protein. GLN1;2 was localized in the vasculature and exhibited low affinities to ammonium (Km = 2450 +/- 150 microm) and glutamate (Km = 3.8 +/- 0.2 mm). The expression of the counterpart vascular tissue-localizing low affinity isoenzyme, GLN1;3, was not stimulated by ammonium; however, the enzyme activity of GLN1;3 was significantly inhibited by a high concentration of glutamate. By contrast, the high affinity isoenzyme, GLN1;1 (Km for ammonium < 10 microm; Km for glutamate = 1.1 +/- 0.4 mm) was abundantly accumulated in the surface layers of roots during nitrogen limitation and was down-regulated by ammonium excess. GLN1;4 was another high affinity-type GS1 expressed in nitrogen-starved plants but was 10-fold less abundant than GLN1;1. These results suggested that dynamic regulations of high and low affinity GS1 isoenzymes at the levels of mRNA and enzyme activities are dependent on nitrogen availabilities and may contribute to the homeostatic control of glutamine synthesis in Arabidopsis roots.

CT fluoroscopy-guided catheterization of the celiac and mesenteric arteries for concurrent CTHA and CTAP

We describe a technique for computed tomographic (CT) fluoroscopy-guided celiac artery or superior mesenteric artery (SMA) catheterization for use with CT hepatic arteriography or CT arterial portography, respectively. Patients underwent conventional hepatic angiography to define the anatomy and to place a catheter within the celiac artery or the SMA. Subsequently, the catheter was repositioned in the target vessels under CT fluoroscopy. Our success rate was 94%.

The transport of prolamine RNAs to prolamine protein bodies in living rice endosperm cells

RNAs that code for the major rice storage proteins are localized to specific subdomains of the cortical endoplasmic reticulum (ER) in developing endosperm. Prolamine RNAs are localized to the ER and delimit the prolamine intracisternal inclusion granules (PB-ER), whereas glutelin RNAs are targeted to the cisternal ER. To study the transport of prolamine RNAs to the surface of the prolamine protein bodies in living endosperm cells, we adapted a two-gene system consisting of green fluorescent protein (GFP) fused to the viral RNA binding protein MS2 and a hybrid prolamine RNA containing tandem MS2 RNA binding sites. Using laser scanning confocal microscopy, we show that the GFP-labeled prolamine RNAs are transported as particles that move at an average speed of 0.3 to 0.4 microm/s. These prolamine RNA transport particles generally move unidirectionally in a stop-and-go manner, although nonlinear bidirectional, restricted, and nearly random movement patterns also were observed. Transport is dependent on intact microfilaments, because particle movement is inhibited rapidly by the actin filament-disrupting drugs cytochalasin D and latrunculin B. Direct evidence was obtained that these prolamine RNA-containing particles are transported to the prolamine protein bodies. The significance of these results with regard to protein synthesis in plants is discussed.

Dual regulated RNA transport pathways to the cortical region in developing rice endosperm

Prolamine and glutelin RNAs are localized to two subdomains of the cortical endoplasmic reticulum (ER), the protein body ER and the cisternal ER, in developing rice seeds. The addition of nearly full-length prolamine sequences at the 3' untranslated region of a reporter RNA redirects its localization from the cisternal ER to the protein body ER. Deletion analysis of prolamine RNA sequences indicates the presence of two partially redundant cis elements required for protein body ER targeting. The addition of glutelin 3' untranslated region to protein body ER cis sequences, however, redirects RNA localization to the cisternal ER. These results indicate that there are at least two regulated RNA transport pathways as well as a constitutive pathway to the cortical ER.

Dual regulated RNA transport pathways to the cortical region in developing rice endosperm

Prolamine and glutelin RNAs are localized to two subdomains of the cortical endoplasmic reticulum (ER), the protein body ER and the cisternal ER, in developing rice seeds. The addition of nearly full-length prolamine sequences at the 3' untranslated region of a reporter RNA redirects its localization from the cisternal ER to the protein body ER. Deletion analysis of prolamine RNA sequences indicates the presence of two partially redundant cis elements required for protein body ER targeting. The addition of glutelin 3' untranslated region to protein body ER cis sequences, however, redirects RNA localization to the cisternal ER. These results indicate that there are at least two regulated RNA transport pathways as well as a constitutive pathway to the cortical ER.

Green revolution: a mutant gibberellin-synthesis gene in rice

The chronic food shortage that was feared after the rapid expansion of the world population in the 1960s was averted largely by the development of a high-yielding semi-dwarf variety of rice known as IR8, the so-called rice 'green revolution'. The short stature of IR8 is due to a mutation in the plant's sd1 gene, and here we identify this gene as encoding an oxidase enzyme involved in the biosynthesis of gibberellin, a plant growth hormone. Gibberellin is also implicated in green-revolution varieties of wheat, but the reduced height of those crops is conferred by defects in the hormone's signalling pathway.

A Ca(2+)-dependent protein kinase that endows rice plants with cold- and salt-stress tolerance functions in vascular bundles

A rice Ca(2+)-dependent protein kinase, OsCDPK7, is a positive regulator commonly involved in the tolerance to cold and salt/drought. We carried out in situ detection of the transcript and immunolocalization of the protein. In the wild-type rice plants under both stress conditions, OsCDPK7 was expressed predominantly in vascular tissues of crowns and roots, vascular bundles and central cylinder, respectively, where water stress occurs most severely. This enzyme was also expressed in the peripheral cylinder of crown vascular bundles and root sclerenchyma. Similar localization patterns with stronger signals were observed in stress-tolerant OsCDPK7 over-expressing transformants with the cauliflower mosaic virus 35S promoter. The transcript of a putative target gene of the OsCDPK7 signaling pathway, rab16A, was also detected essentially in the same tissues upon salt stress, suggesting that the OsCDPK7 pathway operates predominantly in these regions. We propose that the use of the 35S promoter fortuitously strengthened the localized expression of OsCDPK7, resulting in enhancement of the stress signaling in the inherently operating regions leading to improved stress tolerance.

[A patient with Moyamoya-like vessels after radiation therapy for a tumor in the basal ganglia]

A patient with Moyamoya-like vessels after radiation therapy for treatment of a tumor in the basal ganglia is reported. He was diagnosed as Down syndrome at birth. He had a tumor in the left basal ganglionic region at 12 years of the age. The tumor increased in size at age 14. He underwent cerebral angiography, which did not show a stenosis nor occlusion of the internal carotid artery, anterior cerebral artery, nor the middle cerebral artery. He received radiation therapy with a total dose of 56 Gy. He presented a dressing apraxia at age 19. MRI showed cerebral infarction in the left temporo-occipital region. Right internal carotid angiography revealed a severe stenosis of the internal carotid artery and anterior cerebral artery as well as a severe stenosis of the middle cerebral artery on the right side. Moyamoya-like vessels were seen in the basal ganglionic region. Left internal carotid angiography also showed a stenosis of the internal carotid artery and anterior cerebral artery as well as a severe stenosis of the middle cerebral artery on the left side. Moyamoya-like vessels were seen in the basal ganglionic region. Leptomeningeal anastomose and transdural anastomose were bilaterally seen. These arterial occlusion and stenotic phenomenon corresponded to a previous radiation field. These Moyamoya-like vessels with arterial stenosis and occlusion were thought to be due to radiation-induced vasculopathy, because a previous cerebral angiography showed a normal caliber of cerebral arteries. This patient showed that patients with radiation therapy in their early childhood should be carefully observed considering the possibility of this phenomenon.

Inhibition of cancer cell growth by polyinosinic-polycytidylic acid/cationic liposome complex: a new biological activity

A complex of polyinosinic-polycytidylic acid [poly(I) x poly(C)] and cationic liposome (LIC) inhibited the growth of many tumor cell lines at low concentration in vitro, but poly(I) x poly(C) alone had no such antiproliferative effect. The IC50 values of LIC against the tumor cells ranged from 0.1 to 1000 ng/ml. LIC had strong cytotoxic effects on malignant cells of epithelial and fibroblastic origin from various tissues and was also effective against Adriamycin-resistant tumor cells. LIC did not significantly affect the growth of lymphoma cells, leukemia cells, normal diploid fibroblasts, or primary liver cells at concentrations up to 10 microg/ml. The mechanism of the antiproliferative effect of LIC against malignant cells was the induction of apoptosis. LIC induced the fragmentation of nuclear DNA and the degradation of rRNA in tumor cells. The DNA fragmentation occurred within 1-5 h after the addition of LIC, and both the fragmentation and the inhibition of cancer-cell growth were suppressed by a nuclease inhibitor. In contrast, caspase inhibitors did not affect the antiproliferative activity of LIC. These results suggest that LIC induced apoptosis in malignant cells through the direct activation of nucleases and not through the activation of caspases. LIC reduced the incidence and the size of metastatic liver-cancer tumors in two different mouse metastatic liver-cancer models using human colon carcinoma cells. Histochemical analysis revealed that the KM12-HX cells in the tumor nodules were undergoing apoptosis; therefore, LIC also induced the apoptosis of tumor cells in vivo. In these animal models, LIC caused no observed changes in normal hepatocytes.