Unidirectional movement of tracers along the stolon of Saxifraga sarmentosa

Summary When radioactive tracer is applied locally to the stolon of Saxifraga its long-distance movement after 18 hours is found to be strongly polarised; there is in addition a short-distance movement which is unpolarised. With caesium, the long-distance movement is predominantly in the phloem; with strontium in the xylem. These interpretations, a priori probable, were confirmed by artifically reversing, separately, the xylem and the phloem currents. With long pieces of excised stolon only the unpolarised short-distance movement is observed. These results constitute evidence against simultaneous bidirectional translocation in the same sieve tube, and are consistent with either the Münch or the electro-osmotic theory.     

The influence of dinitrophenol on phloem transport along the stolon of Saxifraga sarmentosa

Summary Dinitrophenol in concentrations of 5×10^-3 M applied to the centre 30 cm of 60–70 cm stolons of Saxifraga produces a strong and reversible inhibition of the phloem transport of ¹³⁷Cs or ¹⁴C-assimilates. There is every reason to believe that this effect is localised in the sieve tubes; callose formation does not occur. This evidence is very difficult to reconcile with the Münch hypothesis; it seems on the contrary to demand a theory of active pumping.This work formed part of that submitted for the degree of Ph.D. of London University.     

Movement of [14C]sucrose along the stolon of Saxifraga sarmentosa

Summary The characteristics of ¹³⁷Cs transport along the stolon of Saxifraga previously reported have been confirmed for applied sucrose and natural assimilate. Long-distance transport is strictly unidirectional, with a symmetrical short-distance spread from the point of application. Only the latter takes place in a long piece of excised stolon. Transport is readily reversed when the parent plant is darkened and the daugther, plantlet allowed to photosynthesise. These findings strongly support a mass-flow mechanism for the stolon. They also confirm the value of ¹³⁷Cs as a tracer for assimilate movement, though in contrast to assimilate it suffers appreciable lateral leakage. Pulse labelling of the subtending leaf failed to produce a sharp peak of activity in the stolon. A flattening with time of the ¹⁴C profile is considered to be due to differing linear velocities in parallel sieve tubes.This work formed part of that submitted for the degree, of Ph. D. of the University of London.     

The effect of low temperatures on the phloem transport of radioactive assimilates in the stolon of Saxifraga sarmentosa L.

Abstract. The movement of naturally assimilated ¹⁴C down the stolon of Saxifraga sarmentosa under the influence of localized cold treatments (0°-10°C) applied over lengths up to 10 cm was followed by finding the distribution of tracer at the termination of the experiment. Inhibition is slight at 10°C and very considerable at 0°C. It is very dependent on the length treated, but is definite even when this is only 0.8 cm. Cooling the daughter plantlet to 0°C has a smaller inhibitory effect than might be expected. This is difficult to understand if 'unloading' is metabolic; perhaps the concentration free energy of the sucrose or other solute can be utilized in the sink terminals on the lines of the chemi-osmotic hypothesis. If so the same source of non-respiratory free energy might be available to energize an active sieve-tube mechanism in mid-path chilling experiments.     

The simultaneous movement of two ions in the phloem of the Saxifraga stolon

Summary Paris of tracers were applied simultaneously to the long thin stolons of Saxifraga sarmentosa. After several hours of translocation the very precise pattern of exponential fall-off was examined and interpreted in the light of a model of mass flow with leakage. ⁴²K appears to leak faster than ²²Na; ⁸⁶Rb is very close to ⁴²K. The anion ⁸²Br shows a lower fall-off than ¹³⁷Cs; this is tentatively regarded as due to a much-reduced leakage, though it might imply a higher velocity. The implications of these findings for sieve-tube mechanism are uncertain.This work formed part of that submitted for the degree of Ph.D. of the University of London.     

Translocation in the Stolon of Saxifraga sarmentosa L. The Ultrastructural Background

The ultrastructure of the mature sieve elements of the Saxifragastolon is described. Theseare narrow (3–5 µm) andfairly long (100-300 µm). The sieve plate pores were invariablyfound to be closely-occluded with P-protein. It is argued thatthe double-cutting technique used for excision invalidates thecontention that this must be interpreted as an artifact. TheP-protein filaments appear to consist of a double helix. Stereomicrographs at normal voltages, and at 1 MV in the AEI-EM₇ microscopeare presented.     

The Effect of Inhibitors on Callose Formation in the Sieve Tubes of Saxifraga sarmentosa L.

Electron-microscope studies on stolons undergoing transportinhibition under nitrogen, HCN, and DNP treatment show no evidenceof callose-blockage of the sieve plates. Inhibition must thereforebe interpreted in terms of interruption of the sieve-tube energysupply; this weights the evidence in favour of theories of activemass flow such as those invoking electro-osmosis or proteincontractility.     

The influence of temperature and nitrogen source on growth and nitrogen uptake of two polar-desert species,Saxifraga caespitosa and Cerastium alpinum

Polar-desert plants experience low average air temperatures during their short growing season (4–8 °C mean July temperature). In addition, low availability of inorganic nitrogen in the soil may also limit plant growth. Our goals were to elucidate which N sources can be acquired by polar-desert plants, and how growth and N-uptake are affected by low growth temperatures. We compared rates of N-uptake and increases in mass and leaf area of two polar-desert species (Cerastium alpinum L. and Saxifraga caespitosa L.) over a period of 3 weeks when grown at two temperatures (6 °C vs. 15 °C) and supplied with either glycine, NH₄ ⁺ or NO₃ ⁻. At 15 °C, plants at least doubled their leaf area, whereas there was no change in leaf area at 6 °C. Measured mean N-uptake rates varied between 0.5 nmol g⁻¹ root DM s⁻¹ on glycine at 15 °C and 7.5 nmol g⁻¹ root DM s⁻¹ on NH₄ ⁺ at 15 °C. Uptake rates based upon increases in mass and tissue N concentrations showed that plants had a lower N-uptake rate at 6 °C, regardless of N source or species. We conclude that these polar-desert plants can use all three N sources to increase their leaf area and support flowering when grown at 15 °C. Based upon short-term (8 h) uptake experiments, we also conclude that the short-term capacity to take up inorganic or organic N is not reduced by low temperature (6 °C). However, net N-uptake integrated over a three-week period is severely reduced at 6 °C. This revised version was published online in June 2006 with corrections to the Cover Date.     

The effect of light, salinity, and nitrogen availability on lipid production by Nannochloropsis sp

We examined responses of batch cultures of the marine microalga Nannochloropsis sp. to combined alterations in salinity (13, 27, and 40 g/l NaCl) and light intensity (170 and 700 μmol photons/m²·s). Major growth parameters and lipid productivity (based on total fatty acid determination) were determined in nitrogen-replete and nitrogen-depleted cultures of an initial biomass of 0.8 and 1.4 g/l, respectively. On the nitrogen-replete medium, increases in light intensity and salinity increased the cellular content of dry weight and lipids due to enhanced formation of triacylglycerols (TAG). Maximum average productivity of ca. 410 mg TFA/l/d were obtained at 700 μmol photons/m²·s and 40 g/l NaCl within 7 days. Under stressful conditions, content of the major LC-PUFA, eicosapentaenoic acid (EPA), was significantly reduced while TAG reached 25% of biomass. In contrast, lower salinity tended to improve major growth parameters, consistent with less variation in EPA contents. Combined higher salinity and light intensity was detrimental to lipid productivity under nitrogen starvation; biomass TFA content, and lipid productivity amounted for only 33% of DW and ca. 200 mg TFA/l/day, respectively. The highest biomass TFA content (ca. 47% DW) and average lipid productivity of ca. 360 mg TFA/l/day were achieved at 13 g/l NaCl and 700 μmol photons/m²·s. Our data further support selecting Nannochloropsis as promising microalgae for biodiesel production. Moreover, appropriate cultivation regimes may render Nannochloropsis microalgae to produce simultaneously major valuable components, EPA, and TAG, while sustaining relatively high biomass growth rates.     

The influence of analogs of xanthine on the mutagenic effect of ultraviolet light

Summary Eight compounds can be added to those purine analogs which give synergistic effects with ultraviolet light: 1,3,7,9-tetra-methylxanthine methyl sulfate, 8-chlorocaffeine, ethyltheophylline, 6-dimethylaminopurine, 6-methoxypurine, 8-ethoxycaffeine, 1,3-dimethyl uric acid and 3-methyl uric acid. It appears likely that these are merely representatives of the class of methyl purines, and that other compounds are also active. The synergistic activity varies among the compounds investigated; some give a synergistic effect slightly higher than caffeine, but apparently act by the same mechanism. The height of effect of all of the synergistic purine analogs has been correlated with the stability of the structures determined by inductive effects and steric hindrance. The lack of activity with pyrimidines (l-methyl thymine and 1,3-dimethyluracil) leads to the conclusion that both rings (7,8,9 positions) of the purine molecule are necessary for the synergistic effect.This work was supported by the National Institutes of Health Research Grant AI-05340, the University of Kansas General Research Fund, and an N.I.H. Training Grant (5 T1 GM-703) to the Department of Microbiology.     

Ultrastructural observations of the effect of nitrogen mustard on human chromosomes]

The authors observed in electronic microscopy the methyl-bis-beta chlorethylamine action (nitrogen mustard) on normal human chromosomes. The effects were obtained in vitro after colchicine blocking and on grids after fixation. The action is remarkable on the fiber and on the chromatid's structure.     

The influence of initial posture on the sit-to-stand movement

Head movements, ground reaction forces and electromyographic activity of selected muscles were recorded simultaneously from two subjects as they performed the sit-to-stand manouevre under a variety of conditions. The influence of initial leg posture on the magnitude of the various parameters under investigation was examined first. A preferred initial leg posture resulted in smaller magnitudes of head movement and ground reaction forces. EMG activity in some muscles, trapezius and erector spinae, decreased, while in others, quadriceps and hamstrings, it increased in the preferred leg posture. The decreases seen correlate with reductions in head movement observed. The effect of inhibiting habitual postural adjustments of the head and neck, by comparing "free" and "guided" movements was also examined. In guided movements there are significant reductions in head movement, ground reaction forces and EMG activity in trapezius, sternomastoid and erector spinae. It would appear that both initial leg posture and the abolition of habitual postural adjustment have a profound influence on the efficiency of the sit-to-stand manouevre. This preliminary study high-lights the practical importance of head posture in the diagnosis and treatment of movement disorders, as well as in movement education.     

The effect of light on growth and development of two nitrogen fixing blue-green algae

Summary Green, blue, yellow, red and white light all support spore germination whereas vegetative growth occurs only in red, yellow or white light. This indicates a requirement of nonphotosynthetic light for spore germination and of photosynthetic light for growth and cell divisions. The green or blue light is neither inhibitory to vegetative growth nor to sporulation of red, yellow or white light grown filaments. The growth promoting effect of white light is greater than that of red or yellow light. Whereas spore germination is not affected by the intensity of white light, vegetative growth increases linearly with increase in white light intensity.     

The effect of some pre-ensiling treatments on silage composition and nitrogen disappearance in the rumen

Ryegrass, harvested before ear emergence, was ensiled in triplicate in laboratory silos with and without pre-ensiling treatments. These were: 4.7 M sulphuric acid (39 and 79 g kg^?1 DM); formalin (28 and 58 g kg^?1 DM); ‘Add-F’ (22.5 M formic acid; 36 and 71 g kg^?1 DM); formalin (28 and 58 g kg^?1 DM); ‘Farmline’, a commercial additive containing acids and formalin (31 g kg^?1 DM); heat (30 and 60°C for 1 h); and Lactobacillus plantarum inoculum + glucose (4.6 g kg^?1 DM). The ensilage period was 120 days. Samples of each silage were incubated, in artificial fibre bags, in the rumens of four Hereford-cross steers fitted with permanent rumen cannulae. Total nitrogen (TN) disappearance was measured after incubation periods of 1, 2, 4, 7, 12 and 24 h.Hydrochloric acid and the heating pre-treatments had no significant effect (P > 0.05) on the pH, water-soluble carbohydrates and fermentation acid values compared with those of the control. Fermentation acid production was suppressed to an increasing extent by formalin (28 g kg^?1 DM), sulphuric acid (79 g kg^?1 DM), formic acid (36 g kg^?1 DM), formalin (58 g kg^?1 DM) and formic acid (71 g kg^?1 DM).The application of L. plantarum + glucose increased fermentation acids from 90.3 g kg^?1 DM in the control to 227 g kg^?1 DM, owing to a 10-fold increase in lactic acid content from 21.7 to 202 g kg^?1 DM.All treatments, with the exception of 30°C heating, produced silages with significantly (P < 0.001) more total nitrogen as protein than the control. This ranged from 334 g kg^?1 TN (60°C heating) to 748 g kg^?1 TN (formalin; 58 g kg^?1 DM).All treatments significantly (P < 0.05) reduced TN loss, compared with the control silage values, after a 7-h incubation period in the rumen. After 24 h, however, TN disappearance from the treated silages was not significantly different from that of the control with the exception of the two silages treated with formalin alone. With these silages, the proportion of TN disappearing was 55.0 and 40.0% for the low and high application rates, respectively, compared with a value of 74.0% for the control.     

The purification of luteinizing-hormone-releasing factor with some observations on its properties

Bullock median-eminence tissue was used as a source of luteinizing-hormone-releasing factor for small-scale experiments to explore methods for its isolation. The presence of luteinizing-hormone-releasing factor was detected by the ovulation response in rabbits after intrapituitary infusion of the extract. Gel filtration was found to be suitable for the purification of these extracts. The releasing factor appeared to be a basic peptide of molecular weight in the range 1200-2500. On a larger scale, an extract of hypothalamic tissue from sheep was used to establish a multi-stage isolation procedure that resulted in a 200000-fold purification of luteinizing-hormone-releasing factor. After the initial extraction the isolation process consisted of: (1) two cycles of gel filtration; (2) anion-exchange chromatography; (3) gel filtration in a partially organic medium; (4) thin-layer chromatography on cellulose. Stage (3) separated two zones of activity each containing peptides. One of these was purified further by stage (4) to give a preparation that was active at a dose of 6mug. of peptide/animal, although activity diminished seriously during storage. This preparation contained only five or six components, but the small amounts of peptides obtained at this stage of purity were insufficient for full characterization.