Biomedical subjects

Hilary J Rogers

Publications and source records attributed to Hilary J Rogers.

12 recordsLinked to original sources

PubMed2006

Programmed cell death in floral organs: how and why do flowers die?

BACKGROUND: Flowers have a species-specific, limited life span with an irreversible programme of senescence, which is largely independent of environmental factors, unlike leaf senescence, which is much more closely linked with external stimuli. TIMING: Life span of the whole flower is regulated for ecological and energetic reasons, but the death of individual tissues and cells within the flower is co-ordinated at many levels to ensure correct timing. Some floral cells die selectively during organ development, whereas others are retained until the whole organ dies. TRIGGERS: Pollination is an important floral cell death trigger in many species, and its effects are mediated by the plant growth regulator (PGR) ethylene. In some species ethylene is a major regulator of floral senescence, but in others it plays a very minor role and the co-ordinating signals involved remain elusive. Other PGRs such as cytokinin and brassinosteroids are also important but their role is understood only in some specific systems. MECHANISMS: In two floral cell types (the tapetum and the pollen-tube) there is strong evidence for apoptotic-type cell death, similar to that in animal cells. However, in petals there is stronger evidence for an autophagous type of cell death involving endoplasmic reticulum-derived vesicles and the vacuole. Proteases are important, and homologues to animal caspases, key regulators of animal cell death, exist in plants. However, their role is not yet clear. COMPARISON WITH OTHER ORGANS: There are similarities to cell death in other plant organs, and many of the same genes are up-regulated in both leaf and petal senescence; however, there are also important differences for example in the role of PGRs. CONCLUSIONS: Understanding gene regulation may help to understand cell death in floral organs better, but alone it cannot provide all the answers.

Apoptosis↗

PubMed2005

Ethylene and flower longevity in Alstroemeria: relationship between tepal senescence, abscission and ethylene biosynthesis.

Senescence of floral organs is broadly divided into two groups: those that exhibit sensitivity to exogenous ethylene and those that do not. Endogenous ethylene production from the former group is via a well-characterized biochemical pathway and is either due to developmental or pollination-induced senescence. Many flowers from the order Liliales are characterized as ethylene-insensitive since they do not appear to produce endogenous ethylene, or respond to exogenous ethylene treatments, however, the majority of cases studied are wilting flowers, rather than those where life is terminated by perianth abscission. The role of ethylene in the senescence and abscission of Alstroemeria peruviana cv. Rebecca and cv. Samora tepals was previously unclear, with silver treatments recommended for delaying leaf rather than flower senescence. In the present paper the effects of exogenous ethylene, 2-chloroethylphosphonic acid (CEPA) and silver thiosulphate (STS) treatments on tepal senescence and abscission have been investigated. Results indicate that sensitivity to ethylene develops several days after flower opening such that STS only has a limited ability to delay tepal abscission. Detachment force measurements indicate that cell separation events are initiated after anthesis. Endogenous ethylene production was measured using laser photoacoustics and showed that Alstroemeria senesce independently of ethylene production, but that an extremely small amount of ethylene (0.15 nl flower(-1) h(-1)) is produced immediately prior to abscission. Investigation of the expression of genes involved in ethylene biosysnthesis by semi-quantitative RT-PCR indicated that transcriptional regulation is likely to be at the level of ACC oxidase, and that the timing of ACC oxidase gene expression is coincident with development of sensitivity to exogenous ethylene.

Alstroemeria↗

PubMed2005

Cell death and organ development in plants.

Programmed cell death (PCD) is an important feature of plant development; however, the mechanisms responsible for its regulation in plants are far less well understood than those operating in animals. In this review data from a wide variety of plant PCD systems is analyzed to compare what is known about the underlying mechanisms. Although senescence is clearly an important part of plant development, only what is known about PCD during senescence is dealt with here. In each PCD system the extracellular and intracellular signals triggering PCD are considered and both cytological and molecular data are discussed to determine whether a unique model for plant PCD can be derived. In the majority of cases reviewed, PCD is accompanied by the formation of a large vacuole, which ruptures to release hydrolytic enzymes that degrade the cell contents, although this model is clearly not universal. DNA degradation and the activation of proteases is also common to most plant PCD systems, where they have been studied; however, breakdown of DNA into nucleosomal units (DNA laddering) is not observed in all systems. Caspase-like activity has also been reported in several systems, but the extent to which it is a necessary feature of all plant PCD has not yet been established. The trigger for tonoplast rupture is not fully understood, although active oxygen species (AOS) have been implicated in several systems. In two systems, self incompatibility and tapetal breakdown as a result of cytoplasmic male sterility, there is convincing evidence for the involvement of mitochondria including release of cytochrome c. However, in other systems, the role of the mitochondrion is not clear-cut. How cells surrounding the cell undergoing PCD protect themselves against death is also discussed as well as whether there is a link between the eventual fate of the cell corpse and the mechanism of its death.

Apoptosis↗

PubMed2005

New PCR assay detects rare tooth fungi in wood where traditional approaches fail.

Lu et al. (2002) described a method for identifying Hericium species by PCR, using the primers HT-U1 and HT-L1 which they specifically designed for this purpose. In our hands these primers do not appear to discriminate between tooth fungi and other wood decay species. Therefore PCR primers were designed that discriminated Creolophus cirrhatus from other species (HER2F/HER3R), and which discriminate Hericium alpestre, H. coralloides and H. erinaceus from other wood decay Ascomycota and Basidiomycota but not from each other (HER2F/HER2R). Using the HER2F/HER3R primers together with traditional isolation and direct incubation procedures, the location of C. cirrhatus in Turkey oak logs was mapped. The PCR approach often detected C. cirrhatus in locations where it was suspected to be, based on patterns of staining and decay, but where it was not revealed by isolation onto agar media, emphasising the value of adopting several approaches to unravel fungal community structure in wood.

Basidiomycota↗

PubMed2005

Tobacco BY-2 cells expressing fission yeast cdc25 bypass a G2/M block on the cell cycle.

The mitotic inducer gene from Schizosaccharomyces pombe, Spcdc25, was used as a tool to investigate regulation of G2/M in higher plants using the BY-2 (Nicotiana tabacum) cell line as a model. Spcdc25-expressing BY-2 cells exhibited a reduced mitotic cell size through a shortening of the G2 phase. The cells often formed isodiametric double files both in BY-2 cells and in cell suspensions derived from 35S::Spcdc25 tobacco plants. In Spcdc25-expressing cells, the tobacco cyclin-dependent kinase, NtCDKB1, showed high activity in early S phase, S/G2 and early M phase, whereas in empty vector cells CDKB1 activity was transiently high in early S phase but thereafter remained lower. Spcdc25-expressing cells also bypassed a block on G2/M imposed by the cytokinin biosynthetic inhibitor lovastatin (LVS). Surprisingly, cytokinins were at remarkably low levels in Spcdc25-expressing cells compared with the empty vector, explaining why these cells retained mitotic competence despite the presence of LVS. In conclusion, synchronised Spcdc25-expressing BY-2 cells divided prematurely at a small cell size, and they exhibited premature, but sustained, CDKB1 activity even though endogenous cytokinins were virtually undetectable.

Aphidicolin↗

PubMed2004

Expression of the fission yeast cell cycle regulator cdc25 induces de novo shoot formation in tobacco: evidence of a cytokinin-like effect by this mitotic activator.

During the last decade, the cell cycle and its control by cyclin-dependent kinases (CDKs) has been extensively studied in eukaryotes. The regulation of CDK activity includes, among others, its activation by Cdc25 phosphatase at G2/M. However, within the plant kingdom studies of this regulation have lagged behind and a plant cdc25 homologue has not been identified yet. Here, we report on the effects of transformation of tobacco (Nicotiana tabacum L., cv. Samsun) with fission yeast (Schizosaccharomyces pombe) cdc25 (Spcdc25) on de novo plant organ formation, a process dependent on rate and orientation of cell division. On shoot-inducing medium (low 1-naphthylacetic acid (NAA), high 6-benzylaminopurine (BAP)) the number of shoots formed on internode segments cultured from transgenic plants was substantially higher than in the non-transformed controls. Anatomical observations indicated that the shoot formation process was accelerated but with no changes in the quality and sequence of shoot development. Surprisingly, and in contrast to the controls, when on root-inducing medium (high NAA, low BAP) cultured segments from transgenic plants failed to initiate hardly any roots. Instead, they continued to form shoots at low frequencies. Moreover, in marked contrast to the controls, stem segments from transgenic plants were able to form shoots even without the addition of exogenous growth regulators to the medium. The results indicate that Spcdc25 expression in culture tobacco stem segments mimicked the developmental effects caused by an exogenous hormone balance shifted towards cytokinins. The observed cytokinin-like effects of Spcdc25 transformation are consistent with the concept of an interaction between cell cycle regulators and phytohormones during plant development.

Cell Cycle Proteins↗

PubMed2003

The Arabidopsis 14-3-3 protein, GF14omega, binds to the Schizosaccharomyces pombe Cdc25 phosphatase and rescues checkpoint defects in the rad24- mutant.

The fission yeast (S. pombe) mitotic inducer gene, Spcdc25, interacts with the plant cell cycle to establish a small cell size phenotype compared with wild-type cells. We have investigated the nature of this interaction by yeast two-hybrid screening using Spcdc25 as bait in a cDNA library prepared from root tips of Arabidopsis thaliana (L.) Heynh. Three 14-3-3 proteins were detected: G-box Factor-like (GF)14kappa, lambda and omega; binding with Spcdc25 was confirmed by an independent immunoprecipitation assay. To test for cell cycle checkpoint function, GF14kappa, lambda and omega were transformed independently, using the strong nmt1+ promoter, into rad24-, a fission yeast mutant deficient in a 14-3-3 checkpoint protein. When exposed to UV irradiation or in the presence of 10 mM hydroxyurea, only cells transformed with GF14omega could fully rescue the defects in the DNA-damage and DNA-replication checkpoints of this mutant. Supporting evidence for a GF14omega cell cycle function was provided by semi-quantitative reverse transcription-polymerase chain reaction indicating that expression of this gene was elevated in regions of the plant that comprise dividing cells whereas GF14kappa and lambda expression was more evenly detected in all tissues examined. The data are consistent with the hypothesis that interaction between Spcdc25 and the plant cell cycle occurs at the level of a 14-3-3 protein with distinct checkpoint properties.

Arabidopsis Proteins↗

PubMed2003

Genes encoding two essential DNA replication activation proteins, Cdc6 and Mcm3, exhibit very different patterns of expression in the tobacco BY-2 cell cycle.

Very little is known about the expression patterns in plants of genes that encode proteins involved in the initiation of DNA replication. Partial cDNA sequences that encode Cdc6 and Mcm3 in tobacco have been isolated. The sequences were used as probes in northern blots which suggested that, in the cell cycle of synchronized tobacco BY-2 cells, expression of CDC6 is confined to late G(1) and S-phase whereas the expression of MCM3 is not confined to any particular cell cycle phase. These data were confirmed and extended by real-time PCR measurements of mRNA abundance through the cell cycle. CDC6 exhibits a very clear peak of expression in S-phase whereas MCM3, expressed at a much lower level than CDC6, is not cell-cycle-regulated. These patterns of cell cycle gene expression resemble those found in the fission yeast Schizosaccharomyces pombe rather than those in budding yeast or mammalian cells.

Amino Acid Sequence↗

PubMed2003

Fatty acid elongation is important in the activity of thiocarbamate herbicides and in safening by dichlormid.

The thiocarbamates, such as pebulate (S-propyl butyl (ethyl) thiocarbamate) are a well-established class of herbicides. They inhibit fatty acid elongation, which is necessary for the biosynthesis of constituents of surface waxes and suberin and this has been proposed to be important for their toxicity. In this study lipid metabolism was investigated in herbicide-treated barley (Hordeum vulgare) and a pernicious weed, wild oats (Avena ludoviciana), to test the hypothesis that inhibitory effects on fatty acid elongation could be counteracted by the safer, dichlormid. Pebulate and its sulphoxide derivative (thought to be the active metabolite in vivo) were tested against lipid metabolism in barley or wild oat shoots. In both plants there was a significant inhibition of very long chain fatty acid (VLCFA) synthesis at herbicide concentrations > or =25 micro M. The extent to which safener dichlormid could prevent the inhibition of VLCFA synthesis was different in the two species. Previous treatment of barley with dichlormid (N,N-diallyl-2,2-dichloroacetamide) enabled fatty acid elongation in the presence of pebulate or pebulate sulphoxide, but had no effect on wild oats. The effects on fatty acid elongation mimicked the differential safening action of dichlormid observed on shoot elongation and growth in the two species. These data provide further evidence that inhibition of VLCFA formation is important for the mechanism of action of thiocarbamates.

Acetamides↗

PubMed2002

A WEE1 homologue from Arabidopsis thaliana.

Little is known about the genes that regulate cyclinB-Cdc2 complexes at the G2/M transition of the plant cell cycle although in yeast and animals cdc25 and wee1 are central regulators of cdc2. Here we describe the isolation, by reverse transcription polymerase chain reaction (RT-PCR), of a WEE1 cDNA (AtWEE1) in Arabidopsis thaliana (L.) Heynh. Semi-quantitative RT-PCR showed that AtWEE1 expression was confined to actively dividing regions of the plant. The overexpression of AtWEE1 in fission yeast (Schizosaccharomyces pombe) caused cells to arrest, and to grow but not divide, resulting in very elongated cells. Our data provide evidence for a functional WEE1 in A. thaliana.

Amino Acid Sequence↗

PubMed2002

Cysteine protease gene expression and proteolytic activity during senescence of Alstroemeria petals.

The functional life of the flower is terminated by senescence and/or abscission. Multiple processes contribute to produce the visible signs of petal wilting and inrolling that typify senescence, but one of the most important is that of protein degradation and remobilization. This is mediated in many species through protein ubiquitination and the action of specific protease enzymes. This paper reports the changes in protein and protease activity during development and senescence of Alstroemeria flowers, a Liliaceous species that shows very little sensitivity to ethylene during senescence and which shows perianth abscission 8-10 d after flower opening. Partial cDNAs of ubiquitin (ALSUQ1) and a putative cysteine protease (ALSCYP1) were cloned from Alstroemeria using degenerate PCR primers and the expression pattern of these genes was determined semi-quantitatively by RT-PCR. While the levels of ALSUQ1 only fluctuated slightly during floral development and senescence, there was a dramatic increase in the expression of ALSCYP1 indicating that this gene may encode an important enzyme for the proteolytic process in this species. Three papain class cysteine protease enzymes showing different patterns of activity during flower development were identified on zymograms, one of which showed a similar expression pattern to the cysteine protease cDNA.

Amino Acid Sequence↗

PubMed2002

Characterization of a novel lipoxygenase-independent senescence mechanism in Alstroemeria peruviana floral tissue.

The role of lipoxygenase (lox) in senescence of Alstroemeria peruviana flowers was investigated using a combination of in vitro assays and chemical profiling of the lipid oxidation products generated. Phospholipids and galactolipids were extensively degraded during senescence in both sepals and petals and the ratio of saturated/unsaturated fatty acids increased. Lox protein levels and enzymatic activity declined markedly after flower opening. Stereochemical analysis of lox products showed that 13-lox was the major activity present in both floral tissues and high levels of 13-keto fatty acids were also synthesized. Lipid hydroperoxides accumulated in sepals, but not in petals, and sepals also had a higher chlorophyll to carotenoid ratio that favors photooxidation of lipids. Loss of membrane semipermeability was coincident for both tissue types and was chronologically separated from lox activity that had declined by over 80% at the onset of electrolyte leakage. Thus, loss of membrane function was not related to lox activity or accumulation of lipid hydroperoxides per se and differs in these respects from other ethylene-insensitive floral tissues representing a novel pattern of flower senescence.

Anthocyanins↗