Electron-opaque fibrils and granules in and between the cell walls of higher plants.

The components of higher-plant cell walls which become electron-opaque after staining with ruthenium-osmium were studied by electron microscopy. A fibrillar material which absorbs this stain is a major wall constituent in the root epidermal cells of carrot and morning glory. In both form and size, these fibrils resemble those found on the surface of suspension-cultured cells of the same species Some cells of woody species show an irregular distribution of electron-opaque material in the cell wall matrix and middle lamella. This material, which has an amorphous appearance with many electron stains, is shown by ruthenium-osmium staining to be an aggregate of discrete granules, 150-220 A in diameter. These observations are not consistent with the concept of the cell wall matrix and middle lamella as an amorphous, uniform gel

Lignofibrils on the external cell wall surface of cultured plant cells.

Small strands and bundles of strands extend from the outside surface of suspension-cultured cells of Daucus, Ipomoea, and Phaseolus into the medium. This fibrous cell coat is present in all samples from various growth stages but appears to increase in quantity in the order Ipomoea < Phaseolus < Daucus. The bundles are often many microns in length and display great variation in frequency, size, and form. Identification of the composition of the strands and bundles as lignin is consistent with the following observations: alkaline nitrobenzene oxidation of the strands to compounds which resemble monomers of wood lignin; resistance of the strands to pronase, trypsin, pectinase, and lipase; strong irreversible adsorption of heavy metals; deposition of silver granules by treatment with silver nitrate-hexamine reagent; extraction of the bundles with aqueous dioxane (Björkman procedure); presence in quantity of a structured form of Klason lignin; and existence of material giving a positive test with the Wiesner reagent. Large individual strands (lignofibrils) from Phaseolus show the form of a flat ribbon with very thin branches at irregular intervals. This form does not vary with preparatory techniques, although its electron opacity does. Intercellular spaces display considerable structure and sometimes contain sheets of fibrillar material merging with both the middle lamella between the cells and the surface bundles facing the medium. These sheets are probably another form of association of the lignofibrils. It is suggested that natural fibrous lignin may be a much commoner component of plant tissue than suspected hitherto.

Variability of the iron, copper and mercury contents of individual red blood cells.

The relative iron, copper and mercury contents of individual, isolated erythrocytes from eight people were determined by analytical electron microscopy. The variation in iron content between erythrocytes of the same sample is more than six times, for copper content more than tem times and for mercury more than five times. Similar variations were observed for 1-day-old chick defintive erythrocytes and for 4-day-old chick embryo primitive erythrocytes. The range of variation does not depend greatly, it at all, on the age of the erythroyctes or the tissue of origin. There is little or no correlation between the variation of iron contnet and that of copper. The cause of the wide variation of metallic ion contnt among erythroyctes is not yet known.

Shaping attitudes to postoperative pain relief: the role of the acute pain team.

Postoperative pain relief is often inadequate. Ignorance and misconceptions about opioids by ward staff contribute to this poor management. The introduction of acute pain teams has done much to improve pain relief for patients. It may also have contributed to changes in attitudes and knowledge of medical and nursing staff. We questioned 48 doctors and nurses on their knowledge and beliefs about postoperative pain relief. Staff members were questioned on two units, one with access to an acute pain team and one without. Over half those on the unit using traditional postoperative care thought patients did not receive adequate pain relief (58%). In comparison, only one respondent from the unit with the pain team thought this was the case (P < 0.001). More staff members that had experience of patient-controlled analgesia (PCA) were optimistic about its benefits than those in the unit with no experience; they were also less concerned about possible side effects. Only one respondent on the unit using PCA thought it carried a risk of drug dependence, compared to over half (55%) of those on the unit with no experience in this technique (P < 0.001). Over two-thirds of staff familiar with PCA thought nursing workload had decreased. Acute pain teams have an important role in educating ward staff. The impact of establishing such teams on staff knowledge and attitudes needs further study to ensure that they can carry out this role most effectively.

The mechanism of formation of Cellulose-like microfibrils in a cell-free system from Acetobacter xylinum.

The mechanism of formation of cellulose-like microfibrils by a non-soluble, particulate enzyme and uridine diphosphoglucose (UDPG) in a cell-free system from Acetobacter xylinum was studied by transmission electron microscopy and X-ray diffraction. The suspension of particles to which the enzyme is adsorbed is composed of whole, dense ovoids, 50-250 nm long when wet, of fragments of the ovoids, and amorphous substance. There is a typical unit membrane around each ovoid but initially there is no trace of fibrillar material in the suspension. When the suspension of particles is incubated with UDPG, linear wisps of fibrils are produced which associate rapidly to form longer and wider threads, especially in 0.01 M NaCl. There is no visible attachment of the wisps to the particles. After 20 min incubation, threads with the typical morphology of cellulose microfibrils are formed that later tend to become entangled in clumps. The microfibrils are insoluble in hot, aqueous, alkaline solutions and resistant to the action of trypsin, but may be degraded by glusulase. After treatment with 1 M NaOH at 100° C or with cold 18% NaOH they show an X-ray diffraction pattern which resembles that of Cellulose II from mercerized, authentic bacterial cellulose. Incorporation of radioactive glucose into the insoluble residue is enhanced by drying of the cellulose microfibrils before alkaline digestion and especially by the addition of a gross excess of carrier cellulose after incubation. In this system there is no evidence for participation of linear, axial, synthesizing sites on the cell wall of the bacterium or for ordered, organized granules in the assembly of the microfibrils. That is, cellulose-like microfibrils may be formed in a cell-free system without the action of any of the previously suggested cell organelles. In addition, these observations are consistent with a previously described notion of a transient, hydrated, nascent, bacterial cellulose microfibril. The possibility that cellulose microfibrils of green plants may be formed in the same way is considered.

Morphology microstructure, and development of colonies of Acetobacter xylinum.

Development of the morphology and microstructure of colonies of Acetobacter xylinum growing on agar was studied by optical microscopy, and transmission and scanning electron microscopy. The mass of rapidly dividing cells surrounded by a sheath of cellulose microfibrils passes from a smooth spheroid to a flattened aggregate with a characteristic "pillowed" surface. This morphology is the result of a repeated extrusion of cells from the confirming sheath, followed by regeneration of a new portion of the sheath on the extrusion of cells from the confirming sheath, followed by regeneration of a new portion of the sheath on the extruded cell mass. Relations of this mechanism to others which produce similar shapes are indicated.

Development and evaluation of a dual-pump microcomputer-based closed-loop arterial pressure control system.

Hypertension after cardiac surgery is common and is associated with increased morbidity. It is usually managed by the infusion of short acting vasodilators. The use of a closed-loop computer system to control the infusion of a vasodilator has been shown to compare favourably with manual control. We have developed a closed-loop system for the ATARI 1040ST microcomputer to control arterial pressure by the simultaneous infusion of two vasodilators. The control program is based on a proportional-integral-derivative algorithm which has been adapted to allow control of two IMED 929 infusion pumps from one RS-232 port. All communication between the user and computer is carried out with a 'mouse', thus increasing acceptability of the system to ward staff. Cardiovascular data are collected on-line from the patient monitor via a custom-built analogue to digital convertor. This system was used to study glyceryl trinitrate and sodium nitroprusside in 24 patients requiring vasodilators after cardiopulmonary bypass. The study showed that in 14 of the patients hypertension was controlled by GTN alone and 10 required supplementary SNP. We have demonstrated that this dual-pump automatic arterial pressure control system is a satisfactory and safe method of administering two vasodilators simultaneously. It is suitable for both routine clinical and research uses.

Microcomputer-controlled administration of vasodilators following cardiac surgery: technical considerations.

Hypertension in the early postoperative period after cardiopulmonary bypass is associated with increased morbidity, and is commonly managed by the infusion of short-acting vasodilators. Automatic arterial blood pressure control by closed-loop infusion has been shown to be superior to manual control in several studies. The investigators have developed a closed-loop arterial pressure control system based on the Atari 1040ST microcomputer (Atari, Sunnyvale, CA). The program uses a proportional-integral-derivative control algorithm, developed from that described by Sheppard and his colleagues. The arterial waveform is sampled digitally, and the waveform analysis routine incorporates several artifact detection and rejection functions. Additional safety features are provided in the computer-infusion pump subroutine, which cause alarms to be activated if computer-pump communication fails to occur within a specified time period. A novel feature of this system is the clinical staff's use of a "mouse" to enter data and control the program, which makes keyboard skills unnecessary. This system is in routine service in the cardiac intensive care unit (CICU), both for direct clinical use and for research into various aspects of arterial pressure control, and has proved to be acceptable to the clinical staff.

Automatic control of arterial pressure after cardiac surgery. Evaluation of a microcomputer-based control system using glyceryl trinitrate and sodium nitroprusside.

Arterial hypertension after cardiac surgery is common and is associated with increased morbidity. Glyceryl trinitrate may be a more suitable agent for control of hypertension than sodium nitroprusside. We have developed a closed-loop system for the Atari 1040ST microcomputer to control arterial pressure by the simultaneous infusion of two vasodilators under computer control. Use of this system with glyceryl trinitrate and sodium nitroprusside in 24 patients who required vasodilators after cardiopulmonary bypass, revealed that hypertension was controlled by glyceryl trinitrate alone in 14 of the patients and 10 required supplementary sodium nitroprusside. The results suggest that glyceryl trinitrate is a suitable agent for control of hypertension after cardiac surgery in the majority of patients. They also show that a sizeable minority required additional sodium nitroprusside, and that an automated 'dual pump' system is a satisfactory method of administering two vasodilators in this way.

New evidence for an intermediate polymer of glucose in cellulose biosynthesis by Acetobacter xylinum.

The results of sucrose-density-gradient centrifugation of a cell-free particulate enzyme system from Acetobacter xylinum which was incubated with uridine diphosphoglucose indicate that there is a polymeric intermediate in the biosynthesis of cellulose. This intermediate has the properties of an oligomer of glucose, is normally attached to the heaviest particle of the suspension, but, when released by hydrolysis, is preferentially adsorbed to fragments of preformed cellulose. It may form short segments of microfibrils when precipitated from alkaline solution by ethanol. The presence of this intermediate raises again the question of a primer in cellulose biosynthesis.

Structure and composition of the cell wall of Neurospora crassa.

The structure and composition of the cell walls of hyphae of Neurospora crassa were investigated by electron microscopy, chemical analysis, and X-ray diffraction both before and after progressive enzymatic degradation by snail gut enzymes, chitinase, and trypsin. The wall consists of two phases: randomly disposed skeletal microfibrils of chitin only and an amorphous matrix which contains both beta-glucans and protein. The protein contains a high percentage of the amides of aspartic and glutamic acid but no hydroxy-proline or cysteine. A portion of this protein is a component of or is associated with a system of pores which is embedded in the matrix of the wall. These pores, 40 to 70 A in outside diameter, sometimes branch and seem to provide a three-dimensional network from one side of the wall to the other. They may be a general system of transport across the walls.

Structure of the cell wall of Pythium debaryanum.

The structure of hyphal walls of Pythium debaryanum was investigated by electron microscopy of shadowed replicas and thin sections, before and after digestion by snail gut enzymes or by 1 n HCl at 100 C for 1 hr, and by X-ray diffraction. We found that the wall had two phases, one composed of microfibrils of unknown composition and a second consisting of an amorphous matrix, part of which stained like protein with potassium permanganate and part of which was removed by snail-gut enzymes. In the microfibrillar phase, there were two layers; an outer, thicker layer of randomly disposed microfibrils and an inner, thin layer of microfibrils oriented parallel to the hyphal axis. As in Neurospora crassa, the amorphous phase included a branching system of pores, 40-80 A in diameter. Unlike N. crassa, the cytoplasm of Pythium showed Golgi bodies frequently, and many lomasomes were observed between the cytoplasmic membrane and the wall. The relations between these organelles and the mechanism of wall formation in Pythium are not understood.

Evidence for a beneficial influence of cellulose production on growth ofAcetobacter xylinum in liquid medium.

Cultures of cellulose-deficient cells ofAcetobacter xylinum that were isolated from solid medium revert from the cellulose-deficient condition to the normal, cellulose-producing, form after five transfers in liquid medium. In addition, serial cultures of initial mixtures of cellulose-deficient cells and normal cells in the ratio of 9 to 1 show a rapid decrease in the proportion of deficient cells so that after seven transfers in liquid medium there is less than, 1% of cellulose-deficient cells. These results demonstrate that, in liquid medium, cells which are normal in cellulose production overgrow those which are deficient in this capacity. They are interpreted to suggest that cellulose production in liquid medium helps this obligate aerobe to obtain a limited supply of oxygen by floating the cells close to the surface.

Effect of ketanserin on sodium nitroprusside requirements, arterial pressure control and heart rate following coronary artery bypass surgery.

In a double-blind, placebo controlled study ketanserin, a serotonin S2 antagonist, was administered to hypertensive patients who had undergone coronary artery bypass surgery. Patients were allocated randomly to receive placebo or ketanserin at an infusion rate of 0.05, 1 or 2 mg kg-1 h-1. Sodium nitroprusside was used as escape medication. Ketanserin reduced the nitroprusside requirements and improved the quality of arterial pressure control in all groups, and this was significant in the low- and high-dose groups. There was a significant decrease in heart rate in the low- and high-dose groups compared with placebo, and no effect in patients who received the medium dose of ketanserin. Ketanserin may be a useful treatment for hypertension following coronary artery surgery as it reduced arterial pressure without reflex tachycardia.

The structure of cellulose-producing bacteria, Acetobacter xylinum and Acetobacter acetigenus.

The structure of the pellicles and cells of the cellulose-producing bacteria, Acetobacter xylinum and Acetobacter acetigenus, was studied by transmission electron microscopy of thin sections and freeze-etch replicas of glucose-stimulated cell suspensions, quiescent cell suspensions, and discrete pellicles. These bacteria have a relatively thin cell wall in section, with several irregular features superimposed on an otherwise simple, Gram-negative morphology. There are no flagella or pili. Unfixed, unextracted cells, viewed as whole mounts, show spherical or ellipsoidal bodies of undetermined composition which disappear after extraction with water or ethanol and propylene oxide. For both species, there are several kinds of cell surface irregularities, some of which are localized protrusions of the cell envelope. A variety of irregularities is seen frequently on cells in the first minutes of glucose incubation, on cells in a discrete pellicle, on quiescent cells, and on starved cells. Immediately after the addition of glucose to cellulose-free cells in suspension culture, fine fibrils appear on and (or) near the cell envelope. The fine fibrils are frequently as small as 3 nm in diameter in both freeze-etch and thin-section preparations and are frequently associated with freshly synthesized cellulose fibrils. Starved cells in suspensions free of (classical) microfibrils sometimes reveal stubs of an extracellular structure whose morphology resembles that of a nascent cellulose fibril.