Showing papers by "University of York published in 1996"

Automaticity of social behavior: Direct effects of trait construct and stereotype activation on action.

Abstract: Previous research has shown that trait concepts and stereotypes become active automatically in the presence of relevant behavior or stereotyped-group features. Through the use of the same priming procedures as in previous impression formation research, Experiment l showed that participants whose concept of rudeness was primed interrupted the experimenter more quickly and frequently than did participants primed with polite-related stimuli. In Experiment 2, participants for whom an elderly stereotype was primed walked more slowly down the hallway when leaving the experiment than did control participants, consistent with the content of that stereotype. In Experiment 3, participants for whom the African American stereotype was primed subliminally reacted with more hostility to a vexatious request of the experimenter. Implications of this automatic behavior priming effect for self-fulfilling prophecies are discussed, as is whether social behavior is necessarily mediated by conscious choice processes.

Guidelines for authors and peer reviewers of economic submissions to the BMJ. The BMJ Economic Evaluation Working Party.

Abstract: Over the past decade interest in the economic evaluation of health care interventions has risen1 Reviews of published studies have, however, shown gaps in the quality of work2 3 4 5 As far back as 1974 Williams listed the essential elements of economic evaluations,6 and more recently Drummond and colleagues set out the methodological areas generally agreed among economists7 Guidelines for economic evaluations have been promulgated and reviewed by many bodies,8 9 10 11 12 13 14 but few medical journals have explicit guidelines for peer review of economic evaluations or consistently use economist reviewers for economic papers even though they are a major publication outlet for economic evaluations15 16 17 In January 1995 the BMJ set up a working party on economic evaluation to improve the quality of submitted and published economic articles It was not our intention to be unduly prescriptive or stifle innovative methods; our emphasis is on improving the clarity of economic evaluations We also did not address those issues of conduct that have been emphasised in other guidelines13 14 15 16 17 18 The working party's objectives were to improve the quality of submitted and published economic evaluations by agreeing acceptable methods and their systematic application before, during, and after peer review Its task was to produce: (a) guidelines for economic evaluation, together with a comprehensive supporting statement which could be easily understood by both specialist and non-specialist readers; (b) a checklist for use by referees and authors; and (c) a checklist for use by editors In producing the guidelines the working party has concentrated on full economic evaluations comparing two or more health care interventions and considering both costs and consequences19 Articles sent to the BMJ and other medical journals are often more broadly based “economic …

The dynamical theory of coevolution: a derivation from stochastic ecological processes

Abstract: In this paper we develop a dynamical theory of coevolution in ecological communities. The derivation explicitly accounts for the stochastic components of evolutionary change and is based on ecological processes at the level of the individual. We show that the coevolutionary dynamic can be envisaged as a directed random walk in the community's trait space. A quantitative description of this stochastic process in terms of a master equation is derived. By determining the first jump moment of this process we abstract the dynamic of the mean evolutionary path. To first order the resulting equation coincides with a dynamic that has frequently been assumed in evolutionary game theory. Apart from recovering this canonical equation we systematically establish the underlying assumptions. We provide higher order corrections and show that these can give rise to new, unexpected evolutionary effects including shifting evolutionary isoclines and evolutionary slowing down of mean paths as they approach evolutionary equilibria. Extensions of the derivation to more general ecological settings are discussed. In particular we allow for multi-trait coevolution and analyze coevolution under nonequilibrium population dynamics.

Fair Division: From Cake-Cutting to Dispute Resolution

Abstract: Cutting a cake, dividing up the property in an estate, determining the borders in an international dispute - such problems of fair division are ubiquitous. Fair Division treats all these problems and many more through a rigorous analysis of a variety of procedures for allocating goods (or 'bads' like chores), or deciding who wins on what issues, when there are disputes. Starting with an analysis of the well-known cake-cutting procedure, 'I cut, you choose', the authors show how it has been adapted in a number of fields and then analyze fair-division procedures applicable to situations in which there are more than two parties, or there is more than one good to be divided. In particular they focus on procedures which provide 'envy-free' allocations, in which everybody thinks he or she has received the largest portion and hence does not envy anybody else. They also discuss the fairness of different auction and election procedures.

Automatic Activation of Impression Formation and Memorization Goals: Nonconscious Goal Priming Reproduces Effects of Explicit Task Instructions

Abstract: According to the auto-motive model (J. A. Bargh, 1990), intentions and goals are represented mentally and, as representations, should be capable of nonconscious activation by the environmental context (i.e., "priming"). To test this hypothesis, the authors replicated 2 well-known experiments that had demonstrated differential effects of varying the information-processing goal (impression formation or memorization) on processing the identical behavioral information. However, instead of giving participants the goals via explicit instructions, as had been done in the original studies, the authors primed the impression formation or memorization goal. In both cases, the original pattern of results was reproduced. The findings thus support the hypothesis that the effect of activated goals is the same whether the activation is nonconscious or through an act of will. One's current intentions and goals affect not only what one considers important enough to pay attention to, but also how one uses, interprets, and subsequently remembers that information. Although that is a noncontroversial statement today, it was a radical departure from the dominant view of perception when Bruner and Postman (1948) originally proposed it. To claim that motivation influences perception was a major break with the then-dominant view that perception and judgment were entirely stimulus-driven (Stevens, 1951 ). The result of their claim that needs and motivations influence perception was the "New Look"--a flood of studies demonstrating that an individual's goals greatly influence which information the individual attends to and perceives in the environment, as well as how he or she interprets and remembers that information (Allport, 1955; Bruner, 1951, 1957). Jones and Thibaut (1958) subsequently introduced this idea to the domain of social perception, describing the influence that various potential interaction goals might have on selective attention to and use of information about one's interaction partner. After a period in which motivational and cognitive accounts of phenomena were viewed as mutually exclusive and competing instead of complementary and interdependent (see Gollwitzer & Bargh, 1996; Sorrentino & Higgins, 1986b), there recently has been a significant advance in theory and research on the motivation-cognition interface (e.g., Chaiken, Giner-Sorolla, C Goilwitzer & Moskowitz, 1996; Higgins &

Ethylene as a Signal Mediating the Wound Response of Tomato Plants

Abstract: Plants respond to physical injury, such as that caused by foraging insects, by synthesizing proteins that function in general defense and tissue repair. In tomato plants, one class of wound-responsive genes encodes proteinase inhibitor (pin) proteins shown to block insect feeding. Application of many different factors will induce or inhibit pin gene expression. Ethylene is required in the transduction pathway leading from injury, and ethylene and jasmonates act together to regulate pin gene expression during the wound response.

The time trade-off method: results from a general population study.

Abstract: An important consideration when establishing priorities in health care is the likely effects that alternative allocations of resources will have on health-related quality-of-life (HRQoL). This paper reports on a large-scale national study that elicited the relative valuations attached by the general public to different states of health (defined in HRQoL terms). Health state valuations were derived using the time trade-off (TTO) method. The data from 3395 respondents were highly consistent, suggesting that it is feasible to use the TTO method to elicit valuations from the general public. The paper shows that valuations for severe health states appear to be affected by the age and the sex of the respondent; those aged 18-59 have higher valuations than those aged 60 or over and men have higher valuations than women. These results contradict those reported elsewhere and suggest that the small samples used in other studies may be concealing real differences that exist between population sub-groups. This has important implications for public policy decisions.

Priority encoding transmission

Abstract: We introduce a new method, called priority encoding transmission, for sending messages over lossy packet-based networks. When a message is to be transmitted, the user specifies a priority value for each part of the message. Based on the priorities, the system encodes the message into packets for transmission and sends them to (possibly multiple) receivers. The priority value of each part of the message determines the fraction of encoding packets sufficient to recover that part. Thus even if some of the encoding packets are lost en-route, each receiver is still able to recover the parts of the message for which a sufficient fraction of the encoding packets are received. For any set of priorities for a message, we define a natural quantity called the girth of the priorities. We develop systems for implementing any given set of priorities such that the total length of the encoding packets is equal to the girth. On the other hand, we give an information-theoretic lower bound that shows that for any set of priorities the total length of the encoding packets must be at least the girth. Thus the system we introduce is optimal in terms of the total encoding length. This work has immediate applications to multimedia and high-speed networks applications, especially in those with bursty sources and multiple receivers with heterogeneous capabilities. Implementations of the system show promise of being practical.

Micro-local approach to the Hadamard condition in quantum field theory on curved space-time

Abstract: For the two-point distribution of a quasi-free Klein-Gordon neutral scalar quantum field on an arbitrary four dimensional globally hyperbolic curved space-time we prove the equivalence of (1) the global Hadamard condition, (2) the property that the Feynman propagator is a distinguished parametrix in the sense of Duistermaat and Hormander, and (3) a new property referred to as the wave front set spectral condition (WFSSC), because it is reminiscent of the spectral condition in axiomatic quantum field theory on Minkowski space. Results in micro-local analysis such as the propagation of singularities theorem and the uniqueness up toC∞ of distinguished parametrices are employed in the proof. We include a review of Kay and Wald's rigorous definition of the global Hadamard condition and the theory of distinguished parametrices, specializing to the case of the Klein-Gordon operator on a globally hyperbolic space-time. As an alternative to a recent computation of the wave front set of a globally Hadamard two-point distribution on a globally hyperbolic curved space-time, given elsewhere by Kohler (to correct an incomplete computation in [32]), we present a version of this computation that does not use a deformation argument such as that used in Fulling, Narcowich and Wald and is independent of the Cauchy evolution argument of Fulling, Sweeny and Wald (both of which are relied upon in Kohler's proof). This leads to a simple micro-local proof of the preservation of Hadamard form under Cauchy evolution (first shown by Fulling, Sweeny and Wald) relying only on the propagation of singularities theorem. In another paper [33], the equivalence theorem is used to prove a conjecture by Kay that a locally Hadamard quasi-free Klein-Gordon state on any globally hyperbolic curved space-time must be globally Hadamard.

Economic Growth, Carrying Capacity, and the Environment

Abstract: Nat iona l and international economic policy has usually ignored the environment. In areas where the environment is beginning to impinge on policy, as in the General Agreement on Tariffs and Trade (GATT) and the North American Free Trade Agreement (NAFTA), it remains a tangential concern, and the presumption is often made that economic growth and economic liberalization (including the liberalization of intemational trade) are, in some sense, good for the environment. This notion has meant that economy-wide policy reforms designed to promote growth and liberalization have been encouraged with little regard to their environmental consequences, presumably on the assumption that these consequences would either take care of themselves or could be dealt with separately. In this article we discuss the relation between economic growth and environmental quality, and the link between economic activity and the carrying capacity and resilience of the environment (1).

Cellular and Molecular Actions of Juvenile Hormone. II. Roles of Juvenile Hormone in Adult Insects

Abstract: Publisher Summary Among animal hormones, juvenile hormone (JH) is distinctive because of its unique structure and the diversity of its effects on insect development and reproduction. This chapter reviews the actions of JH on the fat body, gonads, accessory glands, muscle, and nervous system of adult insects. Whereas the epidermis is a major target of premetamorphic JH action, it has been studied little in adult insects, which generally do not moult. However, since the development of yellow pigmentation that accompanies sexual maturation in adult male locusts is clearly dependent on JH-regulation processes, in which cellular and molecular mechanism are investigated. The rapid recent progress in understanding how ecdysteroids regulate the gene activities has resulted from the opportunities afforded by drosophila melanogaster: mapped and characterized mutants, polytene chromosomes with puffs marking active genes, efficient germ-line transformation. The recognition of two aspects of JH action in the tissues of adult insects is reviewed. A model for understanding some aspects of priming by JH may be found in the action of ecdysteroids, where early genes produce factors needed for the expression of late genes. In structure, thyroxine is very different from JH, but there is considerable resemblance between thyroxine and phenoxyphenoxy carbamate, fenoxycarb. Functionally, there are marked similarities. Thyroxine governs metamorphosis in amphibians, but is remarkably pleiotropic in governing many processes ranging from the maturation of the central nervous system to thermoregulation. The chapter emphasizes the importance of selecting insect systems on the basis of their optimal features for research, rather than historical precedent or economic importance. With selection of appropriate systems and application of the cell and molecular research techniques now available, the elusive problem of JH action should soon yield to enlightenment.

Penicillin acylase has a single-amino-acid catalytic centre.

Abstract: PENICILLIN acylase (penicillin amidohydrolase, EC 3.5.1.11) is widely distributed among microorganisms, including bacteria, yeast and filamentous fungi. It is used on an industrial scale for the production of 6-aminopenicillanic acid, the starting material for the synthesis of semi-synthetic penicillins. Its in vivo role remains unclear, however, and the observation that expression of the Escherichia coli enzyme in vivo is regulated by both temperature and phenylacetic acid has prompted speculation that the enzyme could be involved in the assimilation of aromatic compounds as carbon sources in the organism's free-living mode1. The mature E. coli enzyme is a periplasmic 80K heterodimer of A and B chains (209 and 566 amino acids, respectively2,3) synthesized as a single cytoplasmic precursor containing a 26-amino-acid signal sequence to direct export to the cytoplasm4 and a 54-amino-acid spacer between the A and B chains which may influence the final folding of the chains5. The N-terminal serine of the B chain reacts with phenylmethylsulphonyl fluoride, which is consistent with a catalytic role for the serine hydroxyl group. Modifying this serine to a cysteine6'7 inactivates the enzyme, whereas threonine, arginine or glycine substitution prevents in vivo processing of the enzyme7, indicating that this must be an important recognition site for cleavage. Here we report the crystal structure of penicillin acylase at 1.9 A resolution. Our analysis shows that the environment of the catalytically active N-terminal serine of the B chain contains no adjacent histidine equivalent to that found in the serine proteases. The nearest base to the hydroxyl of this serine is its own α-amino group, which may act by a new mechanism to endow the enzyme with its catalytic properties.

A Taxonomy for Multi-Agent Robotics*

Abstract: A key difficulty in the design of multi-agent robotic systems is the size and complexity of the space of possible designs. In order to make principled design decisions, an understanding of the many possible system configurations is essential. To this end, we present a taxonomy that classifies multi-agent systems according to communication, computational and other capabilities. We survey existing efforts involving multi-agent systems according to their positions in the taxonomy. We also present additional results concerning multi-agent systems, with the dual purposes of illustrating the usefulness of the taxonomy in simplifying discourse about robot collective properties, and also demonstrating that a collective can be demonstrably more powerful than a single unit of the collective.

An economic approach to clinical trial design and research priority‐setting

Abstract: Whilst significant advances have been made in persuading clinical researchers of the value of conducting economic evaluation alongside clinical trials, a number of problems remain. The most fundamental is the fact that economic principles are almost entirely ignored in the traditional approach to trial design. For example, in the selection of an optimal sample size no consideration is given to the marginal costs or benefits of sample information. In the traditional approach this can lead to either unbounded or arbitrary sample sizes. This paper presents a decision-analytic approach to trial design which takes explicit account of the costs of sampling, the benefits of sample information and the decision rules of cost-effectiveness analysis. It also provides a consistent framework for setting priorities in research funding and establishes a set of screens (or hurdles) to evaluate the potential cost-effectiveness of research proposals. The framework permits research priority setting based explicitly on the budget constraint faced by clinical practitioners and on the information available prior to prospective research. It demonstrates the link between the value of clinical research and the budgetary restrictions on service provision, and it provides practical tools to establish the optimal allocation of resources between areas of clinical research or between service provision and research.

Biological Diversity, Ecosystems, and the Human Scale

Abstract: This paper considers the significance of biological diversity in relation to large-scale processes in complex and dynamic ecological-economic systems. It focuses on functional diversity, and its relation to production and maintenance of ecological services that underpin human societies. Within functional groups of organisms two important cat- egories of species are identified: keystone process species and those essential for ecosystem resilience. The latter group represents "natural insurance capital." In addition to basic research on the interplay among biological diversity, functional performance, and resilience in complex self-organizing systems, we suggest that a functional approach has two main implications for a strategy for biodiversity conservation: (1) Biodiversity conservation to assure the resilience of ecosystems is required for all systems, no matter how heavily impacted they are. It should not be limited to protected areas. (2) The social, cultural, and economic driving forces in society that cause biodiversity loss need to be addressed directly. Specifically, (a) differences between the value of biological diversity to the private indi- vidual and its fundamental value to society as a whole need to be removed; (b) social and economic policies that encourage biodiversity loss should be reformed, especially where there is a risk of irreversible damage to ecosystems and diversity; and (c) institutions that are adaptive and work in synergy with ecosystem processes and functions are critical and should be created at all levels.

Diversity and phylogeny of rhizobia

Abstract: SUMMARY Rhizobia are the bacteria that form nitrogen-fixing nodules on legumes. The current list of four rhizobium genera and 17 species is reviewed, with some comments on likely future developments in the taxonomy. Sequences of the small subunit ribosomal RNA (SSU or 16S rRNA) support the well-established subdivision of rhizobia into three genera: Rhizobium, Bradyrhizobium and Azorhizobium. These all lie within the alpha subdivision of the Proteabacteria, but on quite distinct branches, each of which also includes many bacterial species that are not rhizobia. Rhizobium, by this definition, is still broad and polyphyletic, so there have recently been suggestions that this genus should be split into four genera. SSU sequences may be the best phylogenetic tool we have, but they are not an infallible guide to evolutionary relationships, particularly among closely related species: slow evolution, recombination, intraspecinc variation and even intragenomic heterogeneity are all limitations that can be illustrated by examples from the rhizobia. It seems likely that the ability to form legume nodules was not present in the common ancestor of all rhizobia but that the nodulation genes were transferred between phylogenetically distinct bacteria, so that the phylogeny of nodulation genes will probably differ from that of the bacteria that carry them. Nitrogen fixation genes are often linked to nodulation genes, but they need not have the same evolutionary history.

Beyond accuracy: Defense and impression motives in heuristic and systematic information processing.

Abstract: (from the chapter) consider the motivations governing information processing within the framework of the heuristic-systematic model / this model proposes 2 concurrent modes by which people process information and reach judgments: a relatively effortless heuristic mode, characterized by the application of simple decision rules (e.g., "experts can be trusted"), and a more effortful and analytic systematic mode, in which particularistic or individuating information about objects of judgment is used / which mode predominates in any situation depends on the individual's current motivation and capacity to engage in detailed processing (chapter) no motivation / accuracy motivation / defense motivation / impression motivation (PsycINFO Database Record)

Oxygen consumption and energy metabolism of the early mouse embryo

Abstract: Oxygen consumption of preimplantation and early postimplantation mouse embryos has been measured using a novel noninvasive ultramicrofluorescence technique, based on an oil-soluble, nontoxic quaternary benzoid compound pyrene, whose fluorescence is quenched in the presence of oxygen. Pyruvate and glucose consumption, lactate production, and glycogen formation from glucose were also measured. Preimplantation mouse embryos of the strain CBA/Ca x C57BL/6 were cultured in groups of 10-30 in 2 microliters of modified M2 medium containing 1 mmol l-1 glucose, 0 mmol l-1 lactate, and 0.33 mmol l-1 pyruvate, for between 4-6 hr. Day 6.5 and 7.5 embryos were cultured singly in 40 microliters M2 medium for between 2-3 hr. Oxygen consumption was detected at all stages of development, including, for the first time, in the early postimplantation embryo. Consumption remained relatively constant from zygote to morula stages before increasing in the blastocyst and day 6.5-7.5 stages. When expressed as QO2 (microliters/mg dry weight/hr), oxygen consumption was relatively constant from the one-cell to morula stages before increasing sharply at the blastocyst stage and declining to preblastocyst levels on days 6.5 and 7.5. Pyruvate was consumed during preimplantation stages, with glucose uptake undetectable until the blastocyst stage. Glucose was the main substrate consumed by the 6.5 and 7.5 day embryo. The proportions of glucose accounted for by lactate appearance were 81%, 86%, and 119% at blastocyst, day 6.5, and day 7.5 stages, respectively. The equivalent figures for glucose incorporated into glycogen were 10.36%, 0.21%, and 0.19%, respectively. The data are consistent with a switch from a metabolism dependent on aerobic respiration during early preimplantation stages to one dependent on both oxidative phosphorylation and aerobic glycolysis at the blastocyst stage, a pattern which is maintained on days 6.5 and 7.5. Our technique for measuring oxygen consumption may have diagnostic potential for selecting viable embryos for transfer following assisted conception techniques in man and domestic animals.

People as Flexible Interpreters: Evidence and Issues from Spontaneous Trait Inference

Abstract: Publisher Summary This chapter investigates the ways in which readily inferences about others occur when inferences are not the focal task. The evidence and issues from spontaneous trait inference (STI) are also discussed in the chapter. STI occurs when attending to another person's behavior produces a trait inference in the absence of explicit intention to infer traits or form an impression of that person. Seven different paradigms have been employed to detect and investigate spontaneous trait inference: (1) cued recall under memory instructions; (2) cued recall of distractors; (3) recognition probe; (4) lexical decision; (5) delayed recognition; (6) word stem completion; and (7) relearning. Informational conditions review the ways in which the trait-relevant information presented in STI studies is systematically varied and its effects. The treatment of cognitive conditions focuses on the efficiency of STI and its minimal demands on cognitive capacity. The motivational conditions are divided into: proximal and distal goals. The chapter also explores whether STI refers to actors or merely to behaviors and the consequences of STI based on awareness, priming, prediction, and correspondence bias.

Getting at the truth or getting along: Accuracy- versus impression-motivated heuristic and systematic processing.

Abstract: Two studies examined the heuristic and systematic processing of accuracy- versus impression-motivated individuals expecting a discussion with a partner believed to hold either a favorable or unfavorable opinion on the discussion issue. Given the goal of having a pleasant interaction, impressionmotivated (versus accuracy-motivated) participants in both studies were particularly likely to express attitudes that were evaluatively consistent with the partner's opinion, reflecting their selective use of a "go along to get along" heuristic. Study 2 yielded stronger evidence for the distinct nature of heuristic and systematic processing in the service of accuracy versus impression goals. In this study, the evaluative implication of impression-motivated participants' low-effort application of a "go along to get along" heuristic biased their more effortful, systematic processing, leading to attitudes consistent with the partner's views. In contrast, given the goal of determining an accurate issue opinion, accuracy-motivated participants exhibited relatively evenhanded systematic processing, resulting in attitudes unbiased by the partner's opinion. The results underscore the utility of a dual-process approach to understanding motivated cognition. Intuition and experience suggest that various motives can influence the way in which people process information and the judgments that result. That is, the motivated perceiver's cognitive processes will be a direct reflection of the goals that they are intended to satisfy. Using the heuristic-systematic model (Chaiken, 1980, 1987; Chaiken, Liberman, & Eagly, 1989) as a theoretical framework, the present research aims to elucidate the distinct ways in which accuracy versus impression motives are served by both heuristic and systematic processes.

Monte carlo study of the interacting self-avoiding walk model in three dimensions

Abstract: We consider self-avoiding walks on the simple cubic lattice in which neighboring pairs of vertices of the walk (not connected by an edge) have an associated pair-wise additive energy. If the associated force is attractive, then the walk can collapse from a coil to a compact ball. We describe two Monte Carlo algorithms which we used to investigate this collapse process, and the properties of the walk as a function of the energy or temperature. We report results about the thermodynamic and configurational properties of the walks and estimate the location of the collapse transition.

Close relationships and adjustment to a life crisis: the case of breast cancer.

Abstract: When life crises occur, significant others are thought to help alleviate distress and resolve practical problems. Yet life crises may overwhelm significant others, eroding their ability to provide effective support. The accuracy of these contrasting accounts of relationship functioning was evaluated in a study of 102 breast cancer patients and their significant others, interviewed at 4 and 10 months after diagnosis. Results largely confirmed the negative account of relationship functioning. Although significant others provided support in response to patients' physical impairment, they withdrew support in response to patients' emotional distress. Moreover, support from significant others did not alleviate patients' distress or promote physical recovery. These results reveal limits to the effectiveness of close relationships in times of severe stress.

Mechanisms of potassium absorption by higher plant roots

Abstract: Potassium, as a plant macronutrient, is accumulated in plant cells from relatively dilute soil solutions and is indispensable for many vital processes. Studies characterising potassium uptake by roots stretch back over many decades. However, it is only with the introduction of modem electrophysiological and molecular techniques that investigations have been possible at a molecular level. Such approaches have confirmed the existence of discrete high and low affinity uptake systems at the root plasma membrane and have greatly enhanced our understanding of the underlying molecular nature of these uptake systems. High affinity K + uptake from micromolar external K + levels is coupled to H + transport as demonstrated independently by patch clamping of single root protoplasts and by studying the transport system after expression in Xenopus oocytes. The measured coupling ratio between the two ions is 1 :1 and is sufficient to account for an accumulation ratio in excess of 10 6 , a value which encompasses experimental observations on K + accumulation. Low affinity K + uptake activates at relatively high external K + levels in the millimolar range and is 'passive' i.e. down the electrochemical gradient for potassium. In two higher plant species single cell inward potassium currents have been identified which are associated with low affinity potassium uptake. Furthermore, specific ion channels which underlie these potassium influxes and form a major constituent of the low affinity potassium uptake pathway have been identified and characterised.