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Howard Griffiths

Publications and source records attributed to Howard Griffiths.

15 recordsLinked to original sources
PubMed2006

Discrimination in the dark. Resolving the interplay between metabolic and physical constraints to phosphoenolpyruvate carboxylase activity during the crassulacean acid metabolism cycle.

A model defining carbon isotope discrimination (delta13C) for crassulacean acid metabolism (CAM) plants was experimentally validated using Kalanchoe daigremontiana. Simultaneous measurements of gas exchange and instantaneous CO2 discrimination (for 13C and 18O) were made from late photoperiod (phase IV of CAM), throughout the dark period (phase I), and into the light (phase II). Measurements of CO2 response curves throughout the dark period revealed changing phosphoenolpyruvate carboxylase (PEPC) capacity. These systematic changes in PEPC capacity were tracked by net CO2 uptake, stomatal conductance, and online delta13C signal; all declined at the start of the dark period, then increased to a maximum 2 h before dawn. Measurements of delta13C were higher than predicted from the ratio of intercellular to external CO2 (p(i)/p(a)) and fractionation associated with CO2 hydration and PEPC carboxylations alone, such that the dark period mesophyll conductance, g(i), was 0.044 mol m(-2) s(-1) bar(-1). A higher estimate of g(i) (0.085 mol m(-2) s(-1) bar(-1)) was needed to account for the modeled and measured delta18O discrimination throughout the dark period. The differences in estimates of g(i) from the two isotope measurements, and an offset of -5.5 per thousand between the 18O content of source and transpired water, suggest spatial variations in either CO2 diffusion path length and/or carbonic anhydrase activity, either within individual cells or across a succulent leaf. Our measurements support the model predictions to show that internal CO2 diffusion limitations within CAM leaves increase delta13C discrimination during nighttime CO2 fixation while reducing delta13C during phase IV. When evaluating the phylogenetic distribution of CAM, carbon isotope composition will reflect these diffusive limitations as well as relative contributions from C3 and C4 biochemistry.

Carbon Dioxide↗
PubMed2006

Competition for pulsed resources: an experimental study of establishment and coexistence for an arid-land grass.

In arid environments, episodically-pulsed resources are important components of annual water and nutrient supply for plants. This study set out to test whether seedlings have an increased capacity for using pulsed resources, which might then improve establishment when in competition with older individuals. A second aim was to determine whether there is a trade-off in competitive strategies when resources are supplied continuously at low concentrations, or as pulses with pronounced inter-pulse periods. A glasshouse experiment used a target-neighbour design of size-asymmetric competition, with juveniles of Panicum antidotale (blue panicgrass) introduced into contrasting densities of adult plants. Stable isotopes of nitrogen were used for measuring plant resource uptake from pulses, and tolerance to inter-pulse conditions was assessed as the mean residence time (MRT) of nitrogen. A higher root/shoot ratio and finer root system enhanced the capacity of juveniles to use resources when pulsed, rather than when continuously supplied. Higher resource uptake during pulses improved the establishment of juvenile Panicum in mixed cultures with older individuals. However, a trade-off was observed in plant strategies, with juveniles showing a lower MRT for nitrogen, which suggested reduced tolerance to resource deficit during inter-pulse periods. Under field conditions, higher utilization of pulsed resources would lead to the improved seedling establishment of Panicum adjacent to "nurse" plants, whereas mature plants with well-developed roots, exploiting a greater soil volume, maintain more constant resource uptake and retention during inter-pulse periods.

Aging↗
PubMed2003

Physiological responses of the CAM epiphyte Tillandsia usneoides L. (Bromeliaceae) to variations in light and water supply.

In an effort to understand the mechanisms that sustain rootless atmospheric plants, the modulation of Crassulacean acid metabolism (CAM) in response to variations in irradiance and water supply was investigated in the epiphyte Tillandsia usneoides. Plants were acclimated to three light regimes, i.e. high, intermediate and low, with integrated photon flux densities (PFD) of 14.40, 8.64 and 4.32 mol m-2 d-1 equivalent to an instantaneous PFD of 200, 100, and 50 mumol m-2 s-1, respectively. Daily watering was then withdrawn from half of the plants at each PFD for 7 d prior to sampling. In response to the three PFD treatments, chlorophyll content increased in plants acclimated to lower irradiances. Light response curves using non-invasive measurements of chlorophyll fluorescence demonstrated that photosystem II efficiency (phi PSII) was maintained in high PFD acclimated plants, as they exhibited a larger capacity for non-photochemical dissipation (NPQ) of excess light energy than low PFD acclimated plants. Net CO2 uptake increased in response to higher PFD, reflecting enhanced carboxylation capacity in terms of phosphoenolpyruvate carboxylase (PEPc) and ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) activities. After water was withdrawn, nocturnal net CO2 uptake and accumulated levels of acidity declined in all PFD treatments, concomitant with increased respiratory recycling of malate. Examining the strategies employed by epiphytes such as T. usneodies to tolerate extreme light and water regimes has demonstrated the importance of physiological mechanisms that allow flexible carboxylation capacity and continued carbon cycling to maintain photosynthetic integrity.

Acclimatization↗
PubMed2002

Integrating diel starch metabolism with the circadian and environmental regulation of Crassulacean acid metabolism in Mesembryanthemum crystallinum.

The diel (24-h) Crassulacean acid metabolism (CAM) cycle in Mesembryanthemum crystallinum (L.) requires rhythmic patterns of transitory starch degradation to produce carbon skeletons for phospho enolpyruvate (PEP) synthesis during the nocturnal Phase I, when PEP carboxylase (PEPc) mediates CO(2) fixation. Under a normal light-dark cycle, nocturnal malate accumulation and nocturnal CO(2) uptake were observed for CAM-induced, but not C(3), M. crystallinum. In both C(3) and CAM plants, transcripts encoding beta-amylase and starch phosphorylase accumulated during the afternoon and declined nocturnally. Under a continuous light regime, ribulose-1,5-bisphosphate carboxylase/oxygenase activity remained co-ordinated with the CAM phases, and circadian abundance patterns were observed for transcripts encoding starch degradative enzymes. Despite circadian PEPc kinase expression, the accumulation of vacuolar malate ceased under continuous light. Exposure to CO(2)-free air for 24 h inhibited starch accumulation over the photoperiod, but re-fixation of respiratory CO(2) resulted in the overnight accumulation of malate to levels comparable to those of control plants. Upon return to normal air, the depleted starch concentration led to stoichiometric decreases in Phase-I CO(2) uptake and malate accumulation. The up-regulation of PEPc kinase transcripts under these conditions was ineffective at sustaining Phase-I CO(2) uptake under starch-limited conditions. We conclude that starch turnover regulates and limits carbon flux through the diel CAM cycle.

Carbon Dioxide↗
PubMed2002

Crassulacean acid metabolism: plastic, fantastic.

The occurrence, activity and plasticity of the CAM pathway is described from an introductory viewpoint, framed by the use of the four "Phases" of CAM as comparative indicators of the interplay between environmental constraints and internal molecular and biochemical regulation. Having described a number of "rules" which seem to govern the CAM cycle and apply uniformly to most species, a number of key regulatory points can then be identified. These include temporal separation of carboxylases, based on the circadian expression of key genes and their control by metabolites. The role of a circadian oscillator and interplay between tonoplast and nuclear control are central to maintaining the CAM cycle. Control of reserve carbohydrates is often neglected, but the importance of daily partitioning (for growth and the subsequent night-time CAM activity) and use at night is shown to drive the CAM cycle. Finally, it is shown that the genotypic and phenotypic plasticity in patterns of CAM expression is mediated partly by environmental conditions and molecular signalling, but also by diffusive constraints in succulent tissues. A transformation system is now required to allow these key areas of control to be elucidated.

Carbohydrate Metabolism↗
PubMed2002

Linking drought-resistance mechanisms to drought avoidance in upland rice using a QTL approach: progress and new opportunities to integrate stomatal and mesophyll responses.

The advent of saturated molecular maps promised rapid progress towards the improvement of crops for genetically complex traits like drought resistance via analysis of quantitative trait loci (QTL). Progress with the identification of QTLs for drought resistance-related traits in rice is summarized here with the emphasis on a mapping population of a cross between drought-resistant varieties Azucena and Bala. Data which have used root morphological traits and indicators of drought avoidance in field-grown plants are reviewed, highlighting problems and uncertainties with the QTL approach. The contribution of root-growth QTLs to drought avoidance appears small in the experiments so far conducted, and the limitations of screening methodologies and the involvement of shoot-related mechanisms of drought resistance are studied. When compared to Azucena, Bala has been observed to have highly sensitive stomata, does not roll its leaves readily, has a greater ability to adjust osmotically, slows growth more rapidly when droughted and has a lower water-use efficiency. It is also a semi-dwarf variety and hence has a different canopy structure. There is a need to clarify the contribution of the shoot to drought resistance from the level of the biochemistry of photosynthesis through stomatal behaviour and leaf anatomy to canopy architecture. Recent advances in studying the physical and biochemical processes related to water use and drought stress offer the opportunity to advance a more holistic understanding of drought resistance. These include the potential use of infrared thermal imaging to study energy balance, integrated and online stable isotope analysis to dissect processes involved in carbon dioxide fixation and water evaporation, and leaf fluorescence to monitor photosynthesis and photochemical quenching. Justification and a strategy for this integrated approach is described, which has relevance to the study of drought resistance in most crops.

Adaptation, Physiological↗
PubMed2002

Differences in delta13C and diameter growth among remnant Scots pine populations in Scotland.

Published data suggest that differences in wood cellulose carbon isotope composition (delta13C) and xylem ring width among natural populations of Scots pine in Scotland (Pinus sylvestris L.) are attributable to the persistence of palaeotypes of various post-glacial migratory origins. We assessed differences in wood cellulose delta13C and ring width among Scottish Scots pine populations grown in a clone bank and in natural stands at various locations in northern and central Scotland. Ring width and wood cellulose delta13C varied significantly among natural stands. Potential water deficit was positively correlated with wood cellulose delta13C and xylem ring width in the natural stands. Neither wood cellulose delta13C nor xylem ring width of clone bank trees correlated with any climate variables at the sites from which the trees originated, indicating little adaptation to climate for these traits. Xylem ring width showed a site x population interaction for the growth sites (i.e., natural stands versus clone bank), but wood cellulose delta13C did not. These results suggest that climate variation in Scotland has not resulted in significant genetic variation in wood cellulose delta13C or xylem ring width in post-glacial populations.

Carbon Isotopes↗
PubMedDate not supplied

Corticosteroids: implications for nursing practice.

Corticosteroids are essential in the management of various inflammatory conditions, but their adverse effects can be a problem. The authors describe the uses and effects of corticosteroids, and discuss the nursing role in minimising problems associated with their use.

Administration, Inhalation↗
PubMedDate not supplied

Administration of medicines. Part 1: The law and nursing.

The authors outline the legal and professional consequences for nurses of failing to adhere to the law relating to the administration of medications. Part 2, next week, will look at the biological consequences for patients of non-adherence to drug administration schedules.

Drug Prescriptions↗
PubMedDate not supplied

Administration of medicines. Part 2: Pharmacology.

In the second part of this article, the authors examine the biological consequences for patients of changes in drug formulation, non-adherence to drug administration schedules and failure to accommodate drug/food interactions.

Drug Administration Schedule↗
PubMedDate not supplied

Nurse prescribing: developing the evaluation agenda.

Nurse prescribing raises complex issues, including erosion of the medical monopoly on control of medication management, compensation for physician shortage and the introduction of guideline-driven prescribing (Jordan and Hughes 1996, McCartney et al 1999). This article sets the recent UK developments in context and discusses the evaluation agenda.

Drug Prescriptions↗
PubMedDate not supplied

Manual handling risk management: critical care beds and support systems.

This article examines the reduction of manual handling risk to nurses through discussion of the technical and ergonomic features of critical care beds and support systems. It describes the features of different types of manual handling equipment, in particular trolleys, beds and patient platform support surfaces.

Beds↗