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Biomedical subjects

L M Weaver

Publications and source records attributed to L M Weaver.

13 recordsLinked to original sources
PubMed2001

Senescence is induced in individually darkened Arabidopsis leaves, but inhibited in whole darkened plants.

It has long been known that leaf senescence can be induced in many plant species by detaching leaves and placing them in the darkness. It recently has been shown that entire Arabidopsis plants placed in the darkness are not induced to senesce, as judged by visible yellowing and certain molecular markers. Here, we show that when individual Arabidopsis leaves are darkened, but not when entire plants are darkened, senescence is induced in the covered leaves. This induction of senescence is highly localized. The phenomenon is leaf age dependent in that it occurs more rapidly and strongly in older leaves than in younger ones, as is the case with many forms of induced senescence. Whole adult plants placed in darkness, in contrast, show delayed senescence, although seedlings lacking primary leaves do not. These observations imply that the light status of the entire plant affects the senescence of individual leaves. A model summarizing the results is presented.

Adaptation, Physiological↗
PubMed1999

Chloroplast-targeted ERD1 protein declines but its mRNA increases during senescence in Arabidopsis.

Arabidopsis ERD1 is a ClpC-like protein that sequence analysis suggests may interact with the chloroplast-localized ClpP protease to facilitate proteolysis. The mRNA encoded by the ERD1 gene has previously been shown to accumulate in response to senescence and to a variety of stresses and hormones. Here we show that the ERD1 protein, in contrast to the ERD1 mRNA, strongly declines in abundance with age, becoming undetectable in fully expanded leaves. Sequence analysis also suggests that ERD1 is chloroplast targeted, and we show in an in vitro system that the native protein is properly imported, processed, and present within the soluble fraction of the chloroplast, presumably the stroma. We show that ClpP protein, which is also present in the stroma, declines with age in parallel with ERD1. These results are consistent with the interaction of ERD1 and ClpP, but they suggest that it is unlikely that either plays a major role during senescence. Certain other chloroplast proteins decline with age coordinately with ERD1 and ClpP, suggesting that these declines are markers of an early age-mediated change that occurs within the chloroplast.

Adenosine Triphosphatases↗
PubMed1998

A comparison of the expression patterns of several senescence-associated genes in response to stress and hormone treatment.

The expression of several Arabidopsis thaliana senescence-associated genes (SAGs) in attached and/or detached leaves was compared in response to age, dehydration, darkness, abscisic acid, cytokinin, and ethylene treatments. Most of the SAGs responded to most of the treatments in a similar fashion. Detachment in darkness and ethylene were the strongest inducers of both SAGs and visible yellowing. Detachment in light was also a strong inducer of SAGs, but not of visible yellowing. The other treatments varied more in their effects on individual SAGs. Responses were examined in both older and younger leaves, and generally were much stronger in the older ones. Individual SAGs differed from the norms in different ways, however, suggesting that their gene products play a role in overlapping but not identical circumstances. Some SAGs responded quickly to treatments, which may indicate a direct response. Others responded more slowly, which may indicate an indirect response via treatment-induced senescence. Four new SAGs were isolated as part of this work, one of which shows strong similarity to late embryogenesis-abundant (Lea) genes.

Abscisic Acid↗
PubMed1996

Characterization of the cDNA and gene coding for the biotin synthase of Arabidopsis thaliana.

Biotin, an essential cofactor, is synthesized de novo only by plants and some microbes. An Arabidopsis thaliana expressed sequence tag that shows sequence similarity to the carboxyl end of biotin synthase from Escherichia coli was used to isolate a near-full-length cDNA. This cDNA was shown to code for the Arabidopsis biotin synthase by its ability to complement a bioB mutant of E. coli. Site-specific mutagenesis indicates that residue threonine-173, which is highly conserved in biotin synthases, is important for catalytic competence of the enzyme. The primary sequence of the Arabidopsis biotin synthase is most similar to biotin synthases from E. coli, Serratia marcescens, and Saccharomyces cerevisiae (about 50% sequence identity) and more distantly related to the Bacillus sphaericus enzyme (33% sequence identity). The primary sequence of the amino terminus of the Arabidopsis biotin synthase may represent an organelle-targeting transit peptide. The single Arabidopsis gene coding for biotin synthase, BIO2, was isolated and sequenced. The biotin synthase coding sequence is interrupted by five introns. The gene sequence upstream of the translation start site has several unusual features, including imperfect palindromes and polypyrimidine sequences, which may function in the transcriptional regulation of the BIO2 gene.

Amino Acid Sequence↗
PubMed1994

Isolation of LUMINIDEPENDENS: a gene involved in the control of flowering time in Arabidopsis.

Plants have evolved the ability to regulate flowering in response to environmental signals such as temperature and photoperiod. The physiology and genetics of floral induction have been studied extensively, but the molecular mechanisms that underlie this process are poorly understood. To study this process, we isolated a gene, LUMINIDEPENDENS (LD), that is involved in the timing of flowering in Arabidopsis. Mutations in this gene render Arabidopsis late flowering and appear to affect light perception. The late-flowering phenotype of the ld mutation was partially suppressed by vernalization. Genomic and cDNA clones of the LD gene were characterized. The predicted amino acid sequence of the LD protein contains 953 residues and includes two putative bipartite nuclear localization signals and a glutamine-rich region.

Alleles↗
PubMed1990

A cDNA encoding 3-deoxy-D-arabino-heptulosonate 7-phosphate synthase from Solanum tuberosum L.

A cDNA encoding potato (Solanum tuberosum L.) 3-deoxy-D-arabino-heptulosonate 7-phosphate synthase, the first enzyme of the shikimate pathway, was cloned into phage lambda gt11. The clone represents the first cDNA for this enzyme from any eukaryotic source. The nucleotide sequence of the cDNA was determined, and its identity was confirmed through partial amino acid sequence analysis of the encoded enzyme. The cDNA contains a 1527-base pair open reading frame that encodes a polypeptide with a calculated molecular weight of 56,153. The amino terminus of the deduced polypeptide resembles a chloroplast transit sequence. Amino acid sequence identities between the mature potato enzyme and the homologous isoenzymes from Escherichia coli are only about 22%. The potato cDNA hybridized to various plant mRNAs that are all about 2 kilobases in size.

3-Deoxy-7-Phosphoheptulonate Synthase↗
PubMed1981

Amphetamine-induced rotation in normal cats.

Amphetamine elicited dose-related rotation (circling behavior) in 9 naive cats; all cats also rotated, at lower rates, during non-drug sessions. The direction of rotation was consistent for each cat, with 6 cats rotating to the right and 3 to the left. The results extend the generality of previous findings involving rodents and suggest that an endogenous asymmetry in striatal dopamine activity may be a common characteristic of many animal species.

Animals↗
PubMed1981

Amphetamine enhancement of reward asymmetry.

Rats with bilaterally implanted lateral hypothalamic electrodes were tested daily for self-stimulation to each side of the brain; rotation (circling behavior) was recorded concomitantly. All rats rotated in a perferred direction regardless of the side of the brain stimulated and all rats had asymmetries in self-stimulation sensitivity (threshold and rate-intensity functions) related to the direction of rotation. Amphetamine both enhanced rotation and potentiated the asymmetry in self-stimulation sensitivity. Subsequently rats were tested in a choice procedure providing concurrent access to rewarding stimulation of either side of the brain; currents were titrated such that, under baseline conditions, rats continually alternated between self-stimulating one side of the brain or the other. Amphetamine induced a robust preference for stimulation to the more sensitive side of the brain (the side having a lower threshold). The results are discussed in relation to mechanisms of drug reinforcement and to biological etiologies of schizophrenia. It is proposed that schizophrenia results from a lateralized overactivity of dopaminergic neuronal systems mediating reward and that amphetamine mimics schizophrenic symptomatology by enhancing lateralization of the same systems.

Amphetamine↗
PubMed1980

Lateralization of reward in rats: differences in reinforcing thresholds.

Fourteen rats with bilaterally implanted lateral hypothalamic electrodes were allowed to self-stimulate each side of the brain during daily test sessions. Rotation (circling behavior) during self-stimulation sessions was also recorded. All rats rotated in preferential direction regardless of the side of the brain stimulated, and, in each case, the direction was the same as that subsequently determined in response to d-amphetamine. All rats had asymmetries in self-stimulation thresholds related to the direction of rotation. Thresholds were lower on the side contralateral to the direction of rotation, and entire rate-intensity functions were displaced to the left on that side. The results, discussed in terms of lateralization of affect, suggest a model in which quantitative differences in neuronal firing can be translated into apparent qualitative specialization, with the two sides of the brain appearing to be specialized for high and low mood, respectively.

Animals↗
PubMed1979

Histochemical identification of acetylcholinesterase in dopaminergic nigrostriatal neurons.

By combining histochemical procedures, evidence was obtained in the rat that acetylcholinesterase (AChE) is contained within perikarya of dopaminergic substantia nigra cells which project to the caudoputamen. Nigrostriatal neurons were identified by retrograde transport of horseradish peroxidase (HRP). Simultaneous incubation of substantia nigra sections for the presence of AChE and HRP demonstrated both reaction products in the same cell bodies. The catecholaminergic nature of these cells was determined by a loss of HRP and AChE reaction products subsequent to intranigral injection of 6-hydroxydopamine.

Acetylcholinesterase↗