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Biomedical subjects

S E Clark

Publications and source records attributed to S E Clark.

At least 19 recordsLinked to original sources
PubMed1997

The CLAVATA1 gene encodes a putative receptor kinase that controls shoot and floral meristem size in Arabidopsis.

The shoot apical meristem is responsible for above-ground organ initiation in higher plants, accomplishing continuous organogenesis by maintaining a pool of undifferentiated cells and directing descendant cells toward organ formation. Normally, proliferation and differentiation are balanced, so that the structure and size of the shoot meristem is maintained. However, Arabidopsis plants homozygous for mutations at the CLAVATA1 (CLV1) locus accumulate excess undifferentiated cells. We describe the molecular cloning and expression pattern of the CLV1 gene. It encodes a putative receptor kinase, suggesting a role in signal transduction. The extracellular domain is composed of 21 tandem leucine-rich repeats that resemble leucine-rich repeats found in animal hormone receptors. We provide evidence that CLV1 expression in the inflorescence is specifically associated with meristematic activity.

Amino Acid Sequence↗
PubMed1997

Does victimization account for sex differences in depressive symptoms?

Women are more depressed than men, and more frequently victimized. We explored the possibility that childhood sexual abuse (CSA) and adult victimization account for the higher levels of depression in women. Depressive symptoms and victimization histories were compared in a sample of 91 men and 76 women seeking out-patient psychotherapy. The women were more depressed, and more likely to have a history of CSA than the men. CSA accounted for a significant proportion of the sex difference in depression levels. The women also were more likely to have been victimized as adults than were the men. However, adult victimization was not associated with higher depression levels, and, therefore, did not account further for the sex difference.

Adult↗
PubMed1997

Acute changes in leucine and phenylalanine kinetics produced by parenteral nutrition in premature infants.

To determine the effect of parenteral nutrition on the balance and catabolism of leucine (by oxidation) and phenylalanine (by hydroxylation) and to assess any acute changes in proteolysis and/or protein synthesis, leucine and phenylalanine kinetics were measured by stable isotope tracer infusions in nine 32-wk gestation premature infants under both basal conditions and in response to an i.v. infusion of glucose, lipid, and amino acids. Leucine and phenylalanine balance both changed from negative to positive during parenteral nutrition. However, leucine and phenylalanine catabolism were differently affected by parenteral nutrition; the rate of leucine oxidation increased 2-fold, whereas the rate of phenylalanine hydroxylation was unchanged from basal values. Phenylalanine utilization for protein synthesis and leucine utilization for protein synthesis (based on both plasma leucine and alpha-ketoisocaproic acid enrichments) increased significantly during parenteral nutrition. The endogenous rates of release of leucine (based on plasma leucine enrichment) and phenylalanine (both reflecting proteolysis) were significantly reduced during parenteral nutrition. The endogenous rate of release of leucine (based on alpha-ketoisocaproic acid enrichment) was slightly but not significantly lower during parenteral nutrition. The substantial increase in leucine oxidation without changes in phenylalanine hydroxylation suggests a possible limitation in the phenylalanine/tyrosine supply during parenteral nutrition. In addition, these results suggest that premature infants respond to parenteral nutrition with acute increases in whole body protein synthesis as well as a probable reduction in proteolysis.

Amino Acids↗
PubMed1996

The CLAVATA and SHOOT MERISTEMLESS loci competitively regulate meristem activity in Arabidopsis.

The CLAVATA (CLV1 and CLV3) and SHOOT MERISTEMLESS (STM) genes specifically regulate shoot meristem development in Arabidopsis. CLV and STH appear to have opposite functions: c1v1 and Clv3 mutants accumulate excess undifferentiated cells in the shoot and floral meristem, while stm mutants fail to form the undifferentiated cells of the shoot meristem during embryonic development. We have identified a weak allele of stm (stm-2) that reveals STM is not only required for the establish- ment of the shoot meristem, but is also required for the continued maintenance of undifferentiated cells in the shoot meristem and for proper proliferation of cells in the floral meristem. We have found evidence of genetic interactions between the CLV and STM loci. clv1 and c1v3 mutations partially suppressed the stm-1 and stm-2 phenotypes, and were capable of suppression in a dominant fashion. clv stm double mutants and plants homozygous for stm but heterozygous for clv, while still lacking an embryonic shoot meristem, exhibited greatly enhanced postembryonic shoot and floral meristem development. Although stm phenotypes are recessive, stm mutations dominantly suppressed clv homozygous and heterozygous phenotypes. These results indicate that the stm phenotype is sensitive to the levels of CLV activity, while the clv phenotype is sensitive to the level of STM activity. We propose that these genes play related but opposing roles in the regulation of cell division and/or cell differentiation in shoot and floral meristems.

Arabidopsis↗
PubMed1995

Grief reactions and recovery in a support group for people bereaved by suicide.

Recent controlled studies have demonstrated that there are few quantitative, but a number of qualitative differences between those bereaved by suicide and those bereaved in other ways. Observations from participants in a support group of those bereaved through suicide are presented here. Guidelines are offered concerning therapy for those who are so clearly distressed by this mode of death.

Adaptation, Psychological↗
PubMed1995

The generation effect and the modeling of associations in memory.

The search of associative memory (SAM) model of Gillund and Shiffrin (1984) was applied to data of two experiments that examined the generation effect (Slamecka & Graf, 1978). Subjects studied a list of related word pairs, in which they either read both words in the pair or generated the right- hand response term using the left-hand stimulus term plus the response word fragment as generation cues. Experiment 1 manipulated encoding condition within subjects and used an incidental learning procedure. Experiment 2 manipulated encoding condition between subjects and used an intentional learning procedure. Memory was tested with recognition, cued recall, and free recall. A higher order association model gave a better and more parsimonious fit to the results than did an item-level association model. The relationship between various versions of SAM and current accounts of the generation effect are discussed, particulary the two-factor theory of Hirshman and Bjork (1988).

Adult↗
PubMed1995

List length and overlap effects in forced-choice associative recognition.

Two experiments examined forced-choice associative recognition for OLAP and NOLAP test conditions. OLAP test trials consist of pairs with overlapping items (e.g., AB vs. AD), whereas NOLAP test trials contain no overlapping items (e.g., AB vs. CF). Previous results show better performance for NOLAP than for OLAP tests, contrary to the predictions of global memory models. The present experiments varied list length to examine the hypothesis that the NOLAP advantage is produced by recall-like retrieval processes. The use of longer lists either eliminated (Experiment 1) or greatly reduced (Experiment 2) the NOLAP advantage. However, a reliable OLAP advantage was not obtained. Implications for models are discussed.

Adult↗
PubMed1994

Word frequency and list composition effects in associative recognition and recall.

The effects of list composition and word frequency on cued recall, associative recognition, and item recognition were examined in three experiments. For pure-frequency lists, cued recall and associative recognition show better performance on common high-frequency (HF) words than on rare low-frequency (LF) words. Item recognition, however, shows an advantage for LF words. In mixed lists, consisting of half HF and half LF words, the HF advantage in cued recall disappeared; however, the word frequency effects in item and associative recognition were unchanged. These results are inconsistent with explanations based on differential attention or co-rehearsal of HF and LF words. However, the results are consistent with list strength results which show that recognition is insensitive to strength-based list composition, but that recall is sensitive to list composition.

Humans↗
PubMed1993

Good grief.

Explore the source record for details and available documents.

Attitude to Death↗
PubMed1993

CLAVATA1, a regulator of meristem and flower development in Arabidopsis.

We have investigated the effects on plant development of mutations in the Arabidopsis thaliana CLAVATA1 gene. In clavata1 plants, vegetative, inflorescence and floral meristems are all enlarged relative to wild type. The apical meristem can fasciate in the more severe mutant alleles, and this fasciation can occur prior to the transition to flowering. Flowers of clavata1 plants can have increased numbers of organs in all four whorls, and can also have additional whorls not present in wild-type flowers. Double mutant combinations of clavata1 with agamous, apetala2, apetala3 and pistillata indicate that CLAVATA1 controls the underlying floral meristem structure upon which these homeotic genes act. Double mutant combinations of clavata1 with apetala1 and leafy indicate CLAVATA1 plays a role in establishing and maintaining floral meristem identity, in addition to its role in controlling meristem size. In support of this, RNA expression patterns of AGAMOUS and APETALA1 are altered in clavata1 flowers.

Arabidopsis↗
PubMed1993

Relation between sports context, competitive trait anxiety, perceived ability, and self-presentation confidence.

This study examined the relations among athletic context, i.e., team-sport versus individual-sport, competitive trait anxiety, perceived ability, and self-presentation confidence for 62 men and 34 women athletes. The analyses showed that the athletic context is associated with variations in competitive trait anxiety and self-presentation confidence; however, no main effect or interaction was noted for perceived ability. Results support the notion that aspects of the sports context are significantly related to various precompetitive cognitions.

Anxiety↗
PubMed1993

A support group for people bereaved through suicide.

Although much research has been performed in recent years on the prevention of suicide, less attention has been focused on helping the persons left behind. This article outlines the history of establishing a support group for people who have been bereaved through suicide in an Australian city. It describes the difficulties in establishing the group, its structure, management, and helping functions, and the experiences gained from the initial 7 years of operation. The article has been written in response to requests from medical, social, and lay agencies for information in establishing similar support groups.

Adaptation, Psychological↗
PubMed1992

Cuing effects and associative information in recognition memory.

Item recognition requires discrimination of studied words from nonstudied words. Associative recognition requires subjects to discriminate studied word groups from recombinations of words from different groups. Cued recognition requires the same old-new discrimination as item recognition, but list items are presented as cues along with the test item. The results from three experiments show (1) little or no effect of cuing for low-frequency words, but (2) positive cuing effects for high-frequency words; (3) increasing levels of overall performance with increases in study time, but (4) unchanging effects of cuing with study time; and (5) stronger positive cuing effects for two cues than for one cue. Five models (Independent Cue Model, Matrix model, MINERVA 2, SAM, and TODAM) were fit to the data of Experiment 1. Each model has trouble with at least one aspect of the results. Theoretical implications and modifications are discussed at length.

Adult↗
PubMed1992

Word frequency effects in associative and item recognition.

The word frequency effect (WFE) has been taken as evidence that recall and recognition are in some way fundamentally different. Consequently, most models assume that recall and recognition operate via very different retrieval mechanisms. Experiment 1 showed that the WFE reverses for associative recognition, which requires discrimination between intact test pairs and recombinations of study list words from different study pairs. Experiment 2, in which word triples were used, revealed an interaction between word frequency and test type: for item recognition, performance was better for low-frequency words; however, for associative recognition and free recall, performance was better for high-frequency words. In Experiment 3, item recognition was tested: although overall performance was better for low-frequency words, the recognition advantage for items in intact pairs was larger for high-frequency words, suggesting two components in recognition memory. These results imply common mechanisms in recall and recognition. Theoretical implications are discussed within the framework of the SAM model.

Adult↗
PubMed1991

Determinants for cleavage of the chlorophyll a/b binding protein precursor: a requirement for a basic residue that is not universal for chloroplast imported proteins.

We demonstrate that the precursor of the major light-harvesting chlorophyll a/b binding protein (LHCP of Photosystem II), encoded by a Type I gene, contains distinct determinants for processing at two sites during in vitro import into the chloroplast. Using precursors from both pea and wheat, it is shown that primary site processing, and release of a approximately 26-kD peptide, depends on an amino-proximal basic residue. Substitution of an arginine at position -4 resulted in an 80% reduction in processing, with the concomitant accumulation of a high molecular weight intermediate. Cleavage occurred normally when arginine was changed to lysine. The hypothesis that a basic residue is a general requirement for transit peptide removal was tested. We find that the precursors for the small subunit of Rubisco and Rubisco activase do not require a basic residue within seven amino acids of the cleavage site for maturation. In the wheat LHCP precursor, determinants for efficient cleavage at a secondary site were identified carboxy to the primary site, beyond what is traditionally called the transit peptide, within the sequence ala-lys-ala-lys (residues 38-41). Introduction of this sequence into the pea precursor, which has the residues thr-thr-lys-lys in the corresponding position, converted it to a substrate with an efficiently recognized secondary site. Our results indicate that two different forms of LHCP can be produced with distinct NH2-termini by selective cleavage of a single precursor polypeptide.

Amino Acid Sequence↗