Nitrate Acts as a Signal to Induce Organic Acid Metabolism and Repress Starch Metabolism in Tobacco.

Nia30(145) transformants with very low nitrate reductase activity provide an in vivo screen to identify processes that are regulated by nitrate. Nia30(145) resembles nitrate-limited wild-type plants with respect to growth rate and protein and amino acid content but accumulates large amounts of nitrate when it is grown on high nitrate. The transcripts for nitrate reductase (NR), nitrite reductase, cytosolic glutamine synthetase, and glutamate synthase increased; NR and nitrite reductase activity increased in leaves and roots; and glutamine synthetase activity increased in roots. The transcripts for phosphoenolpyruvate carboxylase, cytosolic pyruvate kinase, citrate synthase, and NADP-isocitrate dehydrogenase increased; phosphoenolpyruvate carboxylase activity increased; and malate, citrate, isocitrate, and [alpha]-oxoglutarate accumulated in leaves and roots. There was a decrease of the ADP-glucose pyrophosphorylase transcript and activity, and starch decreased in the leaves and roots. After adding 12 mM nitrate to nitrate-limited Nia30(145), the transcripts for NR and phosphoenolpyruvate carboxylase increased, and the transcripts for ADP-glucose pyrophosphorylase decreased within 2 and 4 hr, respectively. Starch was remobilized at almost the same rate as in wild-type plants, even though growth was not stimulated in Nia30(145). It is proposed that nitrate acts as a signal to initiate coordinated changes in carbon and nitrogen metabolism.

Recent advances in ultrasound: high-resolution imaging of superficial structures.

In the past few years, sophisticated ultrasound systems specifically designed for the evaluation of superficial organs and structures have been developed. These "high-resolution" scanners are particularly well suited to diagnostic imaging in the neck. This review summarizes current clinical applications of this evolving technology and highlights initial experience with a prototype scanner that is now commercially available. Particular attention is directed to high-resolution ultrasonography of the thyroid and parathyroid glands, the extracranial carotid arteries, and neoplastic and inflammatory masses of the neck.U

Gray scale ultrasound and the genitourinary tract. A review of clinical applications.

Diagnostic ultrasound has many well established indications in the evaluation of genitourinary tract disease. Musch of this information complements or corroborates findings derived from other investigations. The role of ultrasound as a primary diagnostic modality is still evolving, but it appears to be useful in a variety of clinical situations, especially in azotemia, suspected hydronephrosis, and renal transplantation. Ultrasound also has a place in the evaluation of the retroperitoneum, the perirenal space, and the adrenal glands, and preliminary work suggests a role in prostatic and testicular abnormalities as well. State of the art prospective comparisons with computed tomography need to be made in many of these areas before the precise role of ultrasound can be defined.

Ultrasonography of the salivary glands.

Sonography and computed tomography play complementary roles in imaging mass lesions in the salivary glands and their surroundings. Ninety per cent of parotid tumors originate from the superficial lobe, and we consider sonography to be the method of choice for imaging these lesions. The sensitivity of high-resolution sonography in detecting intraparotid tumors approaches 100 per cent, and ultrasound is therefore an excellent method to evaluate patients with parotid swelling. It may provide clinically useful information by precisely outlining the tumor borders or by detecting multiple or bilateral lesions. We restrict our use of CT to tumors that appear to extend beyond the borders of the parotid gland with possible invasion of surrounding soft tissues or bone. CT is also the method of choice for differentiating lesions of the deep lobe from parapharyngeal tumors and for staging carcinomas. Although ultrasound supplemented with computed tomography should replace conventional sialography in the work-up of parotid neoplasms, sialography remains the method of choice for evaluating patients with chronic sialadenitis, autoimmune diseases, and sialolithiasis. The role of sonography in these conditions is limited to ruling out a parotid neoplasm, assessing the extent of abscess formation, or assisting in localizing calculi in selected patients.

Ultrasonography of the popliteal fossa and lower extremities.

In this article, the numerous proven applications of diagnostic ultrasound to the assessment of disease processes affecting the popliteal fossa and lower extremities have been discussed. Popliteal cysts and aneurysms, hematomas, cellulitis, abscesses, soft tissue neoplasms, and other space-occupying fluid collections are readily identified using this technique. In addition, post-traumatic and inflammatory disorders affecting tendons, synovial thickening and effusion, derangement of articular cartilage, meniscal tears, and alterations in soft tissue thickness as well as foreign bodies are amenable to detection by sonography. With future technologic improvements in transducer design and computerized image reconstruction, diagnostic capabilities of this method in the lower extremities should continue to expand.

Comparison of high resolution real time ultrasonography and high resolution computed tomography in an infant with spinal dysraphism.

An infant with a lumbosacral spinal subcutaneous and intraspinal lipoma involving the conus medullaris was studied with computed tomography and high resolution real time ultrasonography to determine the extent and location of the disease before operation. The high resolution ultrasonogram demonstrated the abnormality with good detail and the added advantage of real time display of the lack of pulsatile mobility of the neural elements, confirming spinal cord tethering. Spinal high resolution ultrasonography is a noninvasive diagnostic tool in infants with spinal abnormalities and should be an important part of a neurosurgeon's diagnostic support system.

Effect of sulfur availability on the integrity of amino acid biosynthesis in plants.

Amino acid levels in plants are regulated by a complex interplay of regulatory circuits at the level of enzyme activities and gene expression. Despite the diversity of precursors involved in amino acid biosynthesis as providing the carbon backbones, the amino groups and, for the amino acids methionine and cysteine, the sulfhydryl group and despite the involvement of amino acids as substrates in various downstream metabolic processes, the plant usually manages to provide relatively constant levels of all amino acids. Here we collate data on how amino acid homeostasis is shifted upon depletion of one of the major biosynthetic constituents, i.e., sulfur. Arabidopsis thaliana seedlings exposed to sulfate starvation respond with a set of adaptation processes to achieve a new balance of amino acid metabolism. First, metabolites containing reduced sulfur (cysteine, glutathione, S-adenosylmethionine) are reduced leading to a number of downstream effects. Second, the relative excess accumulation of N over S triggers processes to dump nitrogen in asparagine, glutamine and further N-rich compounds like ureides. Third, the depletion of glutathione affects the redox and stress response system of the glutathione-ascorbate cycle. Thus, biosynthesis of aromatic compounds is triggered to compensate for this loss, leading to an increased flux and accumulation of aromatic amino acids, especially tryptophan. Despite sulfate starvation, the homeostasis is kept, though shifted to a new state. This adaptation process keeps the plant viable even under an adverse nutritional status.

Sonography of jugular vein thrombosis.

The sonographic findings in three patients with jugular vein thrombosis are described. In each case, intraluminal clot appeared as a solid mass composed of midamplitude echoes. In one patient, near complete resolution of the thrombus was documented by serial sonograms over a 3 month period. High-resolution sonography of the neck is a reliable method to establish the diagnosis of jugular vein thrombosis.

Intrauterine/newborn testicular torsion.

Although spermatic cord torsion in the neonate is uncommon, early recognition with prompt surgical exploration and detorsion of the cord can result in preservation of some testicular tissue. Palpation of the infantile testes can be difficult, and distinguishing testicular from extratesticular abnormalities may not be possible. High-resolution real-time ultrasonography is an effective, noninvasive method of differentiating between the two. If sonography demonstrates and abnormal testicle, prompt surgical exploration is indicated.

High-resolution real-time ultrasonography of neonatal kidneys.

A high-resolution real-time ultrasound system was used to evaluate 43 neonates who had problems referable to the kidney. In addition to a review of normal anatomic features portrayed by this instrument, a variety of pathologic states are illustrated. The system offers the dual advantages of superior spatial resolution and rapid survey capability when compared with traditional articulated-arm contact scanners. As with all sonographic investigations, functional immaturity or depressed organ function is no hindrance to obtaining diagnostic examinations.

Diagnosis of small bowel obstruction: the contribution of diagnostic ultrasound.

The hallmark of intestinal obstruction, whether due to a mechanical cause or to absence of peristalsis, is the intraluminal accumulation of fluid. The presence of air simply makes it easier to visualize dilated fluid-filled loops of plain radiographs. When gas is absent, secondary to vomiting or to cessation of air swallowing, the fluid-filled loops may be difficult to identify. In closed loop obstruction, air cannot enter the involved bowel, and in this situation sonography may provide important information concerning the status of the intestinal tract. In nonstrangulating obstruction, sonography offers confirmatory evidence of dilated fluid-filled loops of bowel. In some instances, ultrasonography may correctly identify the gastrointestinal tract origin of a problem thus enabling appropriate management of the patient. We describe three patients in whom ultrasound enabled prompt diagnosis of fluid-filled loops.

Percutaneous aspiration of adrenal cysts.

Percutaneous needle aspiration was performed in three cases of cystic lesions of the adrenal gland which had been evaluated with nephrotomography, ultrasound, and angiography. The characteristics of the fluid aspirate were used as a guideline to further management. Two lesions were clearly benign cysts and were treated conservatively. The third lesion had a bloody aspirate and was surgically removed. The diagnostic evaluation of adrenal masses should follow a directed approach currently advocated for renal mass lesions.

High resolution real-time sonography of hemodialysis vascular access complications.

Chronic hemodialysis requires an adequately functioning, surgically created vascular access. Many operative techniques have been devised, and each is subject to a variety of complications that significantly shorten the life span of any shunt. Among these are stenosis, thrombosis, aneurysm, pseudoaneurysm, and infection. High resolution sonography is a promising means to evaluate most of these complications. To determine the potential capability of the technique for detecting graft complications, a retrospective review of 30 hemodialysis patients examined with high resolution sonography is presented. Sonographic findings in normal grafts and in a variety of vascular access problems are illustrated.

The subplacental complex: further sonographic observations.

The subplacental complex, which represents vascular channels at the placental-myometrial junction, is a structure that is routinely seen sonographically in patients with posteriorly placed placentas, but not in those with anteriorly placed placentas. This study shows that the subplacental complex is a constant anatomic feature of the placenta regardless of whether it develops on the anterior or posterior uterine wall, and can be visualized in most patients if the subplacental complex is in the focal plane of the transducer. This has important implications in patients with anterior placentas that are being evaluated for abruption or in patients in whom fetal parts lie just beneath the anterior myometrial wall.

Large umbilical cord: a normal finding in some fetuses.

We report two cases in which the umbilical cords of fetuses were large on prenatal ultrasound scans. The pregnancies terminated uneventfully, however, and the babies were healthy at birth and on follow-up visits. We discuss the various etiologies of a large umbilical cord and conclude that, although a large cord may suggest the presence of an underlying abnormality, in some instances it may represent a normal finding.

Positional cloning in Arabidopsis. Why it feels good to have a genome initiative working for you.

Positional (or map-based) cloning techniques are widely used to identify the protein products of genes defined by mutation. In Arabidopsis the information generated by the Genome Initiative is giving this approach a decisive boost. A wealth of sequence polymorphisms and molecular markers is now available and can be exploited for fine mapping with technically simple and robust polymerase chain reaction-based methods. As a result it has become possible to complete positional cloning projects in a short time and with relatively little effort.

Gray scale echographic patterns of hepatic metastatic disease.

Abnormal gray scale hepatic echograms in 76 patients with known or suspected metastatic disease were reviewed. A varied echographic pattern was found, with the gray scale appearances falling into three identifiable categories (dense, lucent, and bulls-eye) and a fourth group difficult to characterize. Prior chemotherapy seemed to have little consistent effect on echographic patterns. A pattern of dense lesions was associated in a large percentage of cases with adenocarcinoma. Carcinoma of the colon commonly produced this appearance. The remaining echographic patterns showed little correlation with specific primary sites or cell types.

Ultrasonographic appearance of adult intussusception.

A gray scale ultrasound evaluation of a case of adult intussusception is presented. The observed "target-like" abdominal mass, with central dense echoes and peripheral sonolucency, may be characteristic of this entity. A primary bowel or intestinal loop process should be considered when a lesion with this appearance is encountered.

Neuroblastoma metastatic to the testis: ultrasonographic screening as an aid to clinical staging.

Secondary testicular tumors are rare, and to our knowledge only a few cases of metastatic neuroblastoma to the testicle have been presented in the literature. We report two cases in which high resolution ultrasonography was helpful in establishing the diagnosis of metastatic neuroblastoma. Because accurate staging is important in the choice of therapy, an aggressive search for the presence of metastatic disease is essential. The small size of the testes in young children makes physical examination difficult, and sonography can be of value.