An improved technique for the culture of jerusalem artichoke (Helianthus tuberosus L.) explants for use in the study of xylem differentiation

An improved technique is described for the culture of explants from Helianthus tuberosus L. (Jerusalem artichoke). No xylem is formed when tuber discs are pre-cultured on a medium containing ßNAA, allowing uninfected discs to be selected for investigation of xylogenesis. Subsequent growth on a medium containing 0.45M 2,4-D and 9.3M kinetin stimulates a high proportion (up to 36%) of the cells to differentiate into xylem elements within a relatively short time (between 1 and 3 d after transfer).     

N-terminal sequence of porcine big gastrin: Sequence, synthesis, and immunochemical studies

The synthesis of fragments corresponding to the N-terminal region of porcine big gastrin is described. Radioimmunoassay using synthetic peptides supports the revised structure for the hormone.     

The low availability of dietary choline for the nutrition of the sheep.

1. Choline, which is present in the diet of the sheep either in the non-esterified form or combined in phospholipids, is rapidly degraded in the rumen. The ultimate product formed from the N-methyl groups is methane. 2. Analysis of the non-esterified choline and the phosphatidylcholine in ruminal and abomasal digesta indicate that the phospholipid is the main vehicle for the passage of choline to the lower digestive tract. 3. The concentration of phosphatidylcholine in abomasal digesta is lower than that of ruminal digesta, which is in line with a selective retention of protozoa in the rumen as observed by others. 4. On defaunation of the rumen to remove ciliated protozoa the concentration of phosphatidylcholine in ruminal digesta falls markedly and becomes lower than that in abomasal digesta. 5. Calculation shows that the adult sheep obtains at most only about 20--25 mg of effective choline per day from its diet (0.002--0.0025% of dietary total dry-weight intake). This is some fifty times less than the minimum required to avoid pathological lesions and death in other species investigated (0.1%+ of dietary dry-weight intake). 6. Sheep liver can synthesize choline from [14C]ethanolamine both in vitro and in vivo, but the synthesis of choline per kg body weight is many times less than it is in the rat. 7. The intact sheep oxidizes an injected dose of [1,2-14C]choline to CO2 at a rate that is several times less than that observed for the rat. This could help to explain the apparent minimal requirement of sheep for dietary choline.     

The invisible copper of cytochrome c oxidase. pH and ATP dependence of its midpoint potential and its role in the oxygen reaction.

Formation of the CO compound has been studied in intact mitochondria, submitochondrial particles and isolated cytochrome oxidase. The reaction requires the prior reduction of both cytochrome a₃ and one other single-electron acceptor. It is inferred that the second acceptor is the “invisible” copper which is undetectable by both optical and spin resonance spectroscopy. The overall process can be viewed as two single electron steps plus a ligand binding reaction. At high concentrations of CO, when titrations are performed at oxidation-reduction potentials significantly above the midpoints of either cytochrome a₃ or “invisible” copper, appearance of the CO compound follows a strict n = 2 (2-electron) relationship. Its midpoint potential is also dependent on the prevailing concentration of CO and is increased by approx. 30 mV for each tenfold increase in the level of CO. At redox potentials approaching the midpoints of cytochrome a₃ or “invisible” copper, significant deviations from n = 2 behavior are apparent which are readily detectable experimentally using low CO concentrations.A mathematical analysis of this model is presented and the oxidation-reduction properties of the CO compound are utilized to determine the midpoint potential of the “invisible” copper. This value is estimated to be 340 ± 10 mV at pH 7.8, independent of pH and the prevailing $\text{sol}\text{[ATP]}\text{[ADP]}\text{× [}\text{P}{}_1\text{]}$ ratio.By analogy with the observations on CO binding, the primary intermediate in the oxidase reaction with oxygen is concluded to be a bridged a₃²⁺-O₂-Cu¹⁺ complex. The initial reduction of molecular oxygen can then proceed via a thermodynamically favorable two-electron step to form a bridged peroxide intermediate. Subsequent reduction to water may later occur by way of two single-electron steps or one two-electron step.     

A study of cell electrophoresis as a means of purifying growth hormone secreting cells

Growth hormone secreting cells of the rat anterior pituitary are heavily laden with granules of growth hormone and can be partially purified on the basis of their resulting high density. Two methods of preparative cell electrophoresis were investigated as methods of enhancing the purification of growth hormone producing cells: density gradient electrophoresis and continuous flows electrophoresis. Both methods provided a two- to four-fold enrichment in growth hormone production per cell relative to that achieved by previous methods. Measurements of electrophoretic mobilities by two analytical methods, microscopic electrophoresis and laser-tracking electrophoresis, revealed very little distinction between unpurified anterior pituitary cell suspensions and somatotroph-enriched cell suspensions. Predictions calculated on the basis of analytical electrophoretic data are consistent with the hypothesis that sedimentation plays a significant role in both types of preparative electrophoresis and the electrophoretic mobility of the growth hormone secreting subpopulation of cells remains unknown.     

Modelling suspended sediment lead concentrations in contaminated peatland catchments using digital terrain analysis

Upland peat soils in close proximity to urban and industrial areas can be contaminated with high concentrations of atmospherically deposited lead. The peat soils of the Peak District (UK) are characterised by extensive eroding gullies. Fine-resolution digital topographic data were used to map the extent and depth of these gullies. Peat samples from eroding gully walls and suspended sediments were collected and analysed for lead content. Variability in lead concentrations of gully wall material and suspended sediments can be explained by differences in mean upslope gully depth. The lead content of suspended sediment exported from catchments characterised by shallow peat gullies is higher than that exported from catchments with deep peat gullies. The empirical relationship between sediment-associated lead concentration and mean upslope gully depth was combined with the gully depth mapping to produce a predictive spatial model of suspended sediment lead concentrations across the Peak District. This model may be particularly useful for catchment managers who are currently involved in the restoration of eroding peat soils in the Peak District uplands.