Functional significance of dauciform roots: exudation of carboxylates and acid phosphatase under phosphorus deficiency in Caustis blakei (Cyperaceae)

Caustis blakei produces an intriguing morphological adaptation by inducing dauciform roots in response to phosphorus (P) deficiency. We tested the hypothesis that these hairy, swollen lateral roots play a similar role to cluster roots in the exudation of organic chelators and ectoenzymes known to aid the chemical mobilization of sparingly available soil nutrients, such as P. Dauciform-root development and exudate composition (carboxylates and acid phosphatase activity) were analysed in C. blakei plants grown in nutrient solution under P-starved conditions. The distribution of dauciform roots in the field was determined in relation to soil profile depth and matrix. The percentage of dauciform roots of the entire root mass was greatest at the lowest P concentration ([P]) in solution, and was suppressed with increasing solution [P], while in the field dauciform roots were predominantely located in the upper soil horizons, and decreased with increasing soil depth. Citrate was the major carboxylate released in an exudative burst from mature dauciform roots, which also produced elevated levels of acid phosphatase activity. Malonate was the dominant internal carboxylate present, with the highest concentration in young dauciform roots. The high concentration of carboxylates and phosphatases released from dauciform roots, combined with their prolific distribution in the organic surface layer of nutrient-impoverished soils, provides an ecophysiological advantage for enhancing nutrient acquisition.

Cytokinin-induced abnormal shoot organogenesis is associated with elevated Knotted1-type homeobox gene expression in tobacco

The molecular mechanisms that regulate the transcription of key developmental genes involved in shoot organogenesis have yet to be fully elucidated. However, it is clear that plant growth regulators, such as cytokinin, play a critical role in the differentiation of adventitious shoots. In Nicotiana tabacum zz100 leaf discs, high frequency shoot formation could be induced with 5 microM of the cytokinin N6-benzyladenine (BA). Increasing the exogenous BA concentration to greater than 20 microM resulted in stunted explants with abnormal shoot morphology and altered mineral composition. Explants with abnormal shoots did not appear to be hyperhydric. Abnormalities were, however, associated with an increase in the expression of a knotted1-type homeobox gene (TobH1) isolated from normal shoot-forming cultures. The results suggest that the development of cytokinin-induced abnormal shoot morphology possibly involves changes in TobH1 gene expression.

Mineral uptake in tobacco leaf discs during different developmental stages of shoot organogenesis

Relationships between mineral uptake and tobacco shoot organogenesis were investigated during three morphogenic phases: phase 1, days 0-10, pre-meristem formation; phase 2, days 10-20, meristem initiation and formation; and phase 3, days 20-35, growth and differentiation of induced meristems into leafy shoots. The mineral content of both shoot-forming (SF) and non-shoot-forming (NSF) media was examined over the 35-day culture period. Both SF and NSF explants rapidly consumed iron during phase 1. Nitrate uptake in SF explants was high and independent of explant growth during phases 1 and 2, but greatest and strongly correlated with growth during phase 3. Phosphorus uptake was highest in SF explants during phases 2 and 3, and correlated with explant growth. Uptake of potassium, calcium and sulphur was strongly associated with explant growth during phase 3 whereas magnesium uptake was only poorly correlated with growth. Results from this study indicate that particular minerals may have an important role in regulating development as well as generally supporting growth.

Inorganic nitrogen requirements during shoot organogenesis in tobacco leaf discs

The role of nitrate, ammonium, and culture medium pH on shoot organogenesis in Nicotiana tabacum zz100 leaf discs was examined. The nitrogen composition of a basal liquid shoot induction medium (SIM) containing 39.4 mM and 20.6 mM was altered whilst maintaining the overall ionic balance with Na(+) and Cl(-) ions. Omission of total nitrogen and nitrate, but not ammonium, from SIM prevented the initiation and formation of shoots. When nitrate was used as the sole source of nitrogen, a high frequency of explants initiated and produced leafy shoots. However, the numbers of shoots produced were significantly fewer than the control SIM. Buffering nitrate-only media with the organic acid 2[N-morpholino]ethanesulphonic acid (MES) could not compensate for the omission of ammonium. Ammonium used as the sole source of nitrogen appeared to have a negative effect on explant growth and morphogenesis, with a significant lowering of media pH. Buffering ammonium-only media with MES stabilized pH and allowed a low frequency of explants to initiate shoot meristems. However, no further differentiation into leafy shoots was observed. The amount of available nitrogen appears to be less important than the ratio between nitrate and ammonium. Shoot formation was achieved with a wide range of ratios, but media containing 40 mM nitrate and 20 mM ammonium (70:30) produced the greatest number of shoots per explant. Results from this study indicate a synergistic effect between ammonium and nitrate on shoot organogenesis independent of culture medium pH.

Inorganic nitrogen requirements during shoot organogenesis in tobacco leaf discs

The role of nitrate, ammonium, and culture medium pH on shoot organogenesis in Nicotiana tabacum zz100 leaf discs was examined. The nitrogen composition of a basal liquid shoot induction medium (SIM) containing 39.4 mM and 20.6 mM was altered whilst maintaining the overall ionic balance with Na(+) and Cl(-) ions. Omission of total nitrogen and nitrate, but not ammonium, from SIM prevented the initiation and formation of shoots. When nitrate was used as the sole source of nitrogen, a high frequency of explants initiated and produced leafy shoots. However, the numbers of shoots produced were significantly fewer than the control SIM. Buffering nitrate-only media with the organic acid 2[N-morpholino]ethanesulphonic acid (MES) could not compensate for the omission of ammonium. Ammonium used as the sole source of nitrogen appeared to have a negative effect on explant growth and morphogenesis, with a significant lowering of media pH. Buffering ammonium-only media with MES stabilized pH and allowed a low frequency of explants to initiate shoot meristems. However, no further differentiation into leafy shoots was observed. The amount of available nitrogen appears to be less important than the ratio between nitrate and ammonium. Shoot formation was achieved with a wide range of ratios, but media containing 40 mM nitrate and 20 mM ammonium (70:30) produced the greatest number of shoots per explant. Results from this study indicate a synergistic effect between ammonium and nitrate on shoot organogenesis independent of culture medium pH.

Influence of BA and sucrose on the competence and determination of pepper (Capsicum annuum L. var. Sweet Banana) hypocotyl cultures during shoot formation

The simultaneous presence of 6-benzyladenine (BA) and sucrose in a Murashige and Skoog medium (SIM) during the initial stages of shoot initiation have been found to be obligatory for high-frequency shoot formation in the Capsicum annuum L. var. 'Sweet Banana' upper hypocotyl explants. The explants are determined for shoot formation following a minimum of 8 days of culture on SIM. Deprivation of exogenous sucrose from day 6 to day 20 of culture had no effect on the shoot forming response of the explants. BA and sucrose appear to act independently on different aspects of the competence of explants to respond to SIM during shoot initiation.

Interhospital Transfers by Helicopter: The First 50 Patients of the Careflight Project

An interhospital helicopter transfer service was set up using a dedicated helicopter fitted with medical equipment and staffed by anaesthetists. The system proved to be safe and practical.

Fifty patients were referred from 38 hospitals throughout the UK, with 84% of transfers preplanned. Patients were transferred a mean distance of 118 miles (range 35–397 miles) and there was no deterioration during transfer as measured by pre and post transfer sickness scores. Twenty-eight per cent of cases could not have been practically transferred by conventional means.

The death rate of 20% was lower than that reported for specially equipped and staffed land transfer systems, which may indicate less physiological deterioration in the critically ill compared to road transfer. Dedicated helicopter transfer resulted in a 50% survival rate in patients with a sickness score over 18, a group found not to survive after land transfer. There was no correlation between distance moved and outcome.

A helicopter transfer system using suitable equipment and staff is a practical and safe method of moving critically ill patients between hospitals, and may be preferable to land transfer for distances in excess of 25 miles.

A new portable oxygen system using liquid oxygen

Liquid oxygen provides both practical and financial advantages in comparison with compressed oxygen when transferring patients within and between hospitals. We describe a portable liquid oxygen system and evaluate its uses and shortcomings in this area.

The cardiovascular effect of vasopressin in relation to its plasma concentration in man and its relevance to high blood pressure

The cardiovascular response and the changes of plasma arginine vasopressin (AVP) concentration following graded doses of AVP infused intravenously have been defined in six normal young men. The same measurements were also made during fluid deprivation in a patient with both nephrogenic diabetes insipidus and systemic hypertension. When, following AVP infusion, mean diastolic arterial pressure increased from 72 +/- 3 mmHg (SEM) to 78 +/- 2 mmHg (SEM) in the normal subject group, mean plasma AVP increased by 14.5 fmol/ml. When the patient was deprived of water, diastolic pressure increased, despite the fluid loss, from 90 to 105 mmHg, with a comparable increase of plasma AVP concentration of 15.3 fmol/ml. Further increases of plasma AVP concentration in either the normal subjects or in the patient were not associated with further increments of arterial pressure. We suggest that under pathophysiological circumstances in man plasma AVP concentrations may achieve levels which have a significant cardiovascular effect.

Radioimmunoassay of arginine-vasopressin in human urine and its use in physiological and pathological states

A highly specific radioimmunoassay for arginine-vasopressin (AVP) in human urine has been developed, with a detection limit of 2.2 fmol/ml. The mean recovery of added AVP was 99.5 +/- 3.1 (S.D.)% when correction was made for the fact that an inverse relationship was observed between the recovery of AVP and the osmolality of the urine. The intra- and interassay coefficients of variation were 3.5--7 and 2.5--10% respectively. Arginine-vasopressin remains stable in urine after repeated freezing and thawing after storage at 4 or 20 degrees C for up to 7 days and at -20 degrees C for more than 3 months. During unrestricted fluid intake in normal people, the mean rate of renal excretion of AVP was 95 +/- 68 (S.D.) fmol/min. An isosmotic reduction of 9% in the plasma volume increased the excretion of AVP to 259 +/- 147 (S.D.) fmol/min. At the height of water-induced diuresis the rate of excretion fell to 70 +/- 28 (S.D.) fmol/min. Fluid deprivation for 18 h produced a moderate but significant increase in mean excretion of AVP, to a value of 116 +/- 67 (S.D.) fmol/min. Patients with compulsive water drinking showed a normal relationship between urine osmolality and the rate of excretion of AVP. In pituitary diabetes insipidus, AVP was undetectable, whereas in hereditary nephrogenic diabetes insipidus a progressive increase in the rate of excretion of AVP was observed in response to dehydration. There was a wide variation in the rate of excretion of AVP (range 126--8704 fmol/min) in patients with unexplained hyponatraemia, presumed to be due to an inappropriate secretion of antidiuretic hormone. Despite this variation, the relationship between urine osmolality and the rate of excretion of AVP clearly differed from that observed in normal people.

Vasovagal hypotension and vasopressin release

Mild vasovagal hypotension occurred in two normal male volunteers during insertion of indwelling venous cannulae. In spite of a rapid intravenous fluid load (3.6-4.6 litres in 90 min) both subjects passed little urine for 100 min. When the experiment was repeated without vasovagal hypotension, a rapid large diuresis followed the fluid load. The prolonged oliguria after vasovagal hypotension was the result of vasopressin release. This was demonstrated by measuring vasopressin in the blood and urine and by observing the renal response to a water load. The observation in man that a mild transient hypotensive episode may reduce urine flow for 100 min has clinical significance.