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Biomedical subjects

Wouter G van Doorn

Publications and source records attributed to Wouter G van Doorn.

12 recordsLinked to original sources
PubMed2007

Gene expression in opening and senescing petals of morning glory (Ipomoea nil) flowers.

We isolated several senescence-associated genes (SAGs) from the petals of morning glory (Ipomoea nil) flowers, with the aim of furthering our understanding of programmed cell death. Samples were taken from the closed bud stage to advanced visible senescence. Actinomycin D, an inhibitor of transcription, if given prior to 4 h after opening, suppressed the onset of visible senescence, which occurred at about 9 h after flower opening. The isolated genes all showed upregulation. Two cell-wall related genes were upregulated early, one encoding an extensin and one a caffeoyl-CoA-3-O-methyltransferase, involved in lignin production. A pectinacetylesterase was upregulated after flower opening and might be involved in cell-wall degradation. Some identified genes showed high homology with published SAGs possibly involved in remobilisation processes: an alcohol dehydrogenase and three cysteine proteases. One transcript encoded a leucine-rich repeat receptor protein kinase, putatively involved in signal transduction. Another transcript encoded a 14-3-3 protein, also a protein kinase. Two genes have apparently not been associated previously with senescence: the first encoded a putative SEC14, which is required for Golgi vesicle transport, the second was a putative ataxin-2, which has been related to RNA metabolism. Induction of the latter has been shown to result in cell death in yeast, due to defects in actin filament formation. The possible roles of these genes in programmed cell death are discussed.

Dactinomycin↗
PubMed2006

DNA degradation and nuclear degeneration during programmed cell death in petals of Antirrhinum, Argyranthemum, and Petunia.

Programmed cell death (PCD) was studied in the petals of Antirrhinum majus, Argyranthemum frutescens, and Petunia hybrida, using DNA degradation and changes in nuclear morphology as parameters. The petals exhibit loss of turgor (wilting) as a visible symptom of PCD. DNA degradation, as shown on agarose gels, occurred in all species studied, prior to visible wilting. The number of DNA masses in all the petals of a flower, determined by flow cytometry, markedly increased in Argyranthemum and Petunia, but decreased in Antirrhinum. Many small DNA masses were observed in Argyranthemum and Petunia. The surface of each small DNA mass stained with the lipophilic fluorochrome 3,3'-dihexyloxacarbocyanine iodide (DiOC6), indicating that these masses were surrounded by a membrane. In Antirrhinum, in contrast, the chromatin fragmented into several small spherical clumps that remained inside a large membranous structure. Nuclear fragmentation, therefore, did not occur in Antirrhinum, whereas nuclear fragmentation possibly was a cause of the small DNA masses in Argyranthemum and Petunia. It is concluded that at least two contrasting nuclear morphologies exist during PCD. In the first, the chromatin fragments inside the nucleus, not accompanied--or followed--by nuclear fragmentation. In the second, a large number of DNA masses were observed each enveloped by a membrane. The second type was probably due, at least partially, to nuclear fragmentation.

Antirrhinum↗
PubMed2006

Nuclear fragmentation and DNA degradation during programmed cell death in petals of morning glory (Ipomoea nil).

We studied DNA degradation and nuclear fragmentation during programmed cell death (PCD) in petals of Ipomoea nil (L.) Roth flowers. The DNA degradation, as observed on agarose gels, showed a large increase. Using DAPI, which stains DNA, and flow cytometry for DAPI fluorescence, we found that the number of DNA masses per petal at least doubled. This indicated chromatin fragmentation, either inside or outside the nucleus. Staining with the cationic lipophilic fluoroprobe DiOC6 indicated that each DNA mass had an external membrane. Fluorescence microscopy of the nuclei and DNA masses revealed an initial decrease in diameter together with chromatin condensation. The diameters of these condensed nuclei were about 70% of original. Two populations of nuclear diameter, one with an average diameter about half of the other, were observed at initial stages of nuclear fragmentation. The diameter of the DNA masses then gradually decreased further. The smallest observed DNA masses had a diameter less than 10% of that of the original nucleus. Cycloheximide treatment arrested the cytometrically determined changes in DNA fluorescence, indicating protein synthesis requirement. Ethylene inhibitors (AVG and 1-MCP) had no effect on the cytometrically determined DNA changes, suggesting that these processes are not controlled by endogenous ethylene.

Apoptosis↗
PubMed2005

Many ways to exit? Cell death categories in plants.

Programmed cell death (PCD) is an integral part of plant development and defence. It occurs at all stages of the life cycle, from fertilization of the ovule to death of the whole plant. Without it, tall trees would probably not be possible and plants would more easily succumb to invading microorganisms. Here, we have attempted to categorize plant PCD in relation to three established morphological types of metazoan cell death: apoptosis, autophagy and non-lysosomal PCD. We conclude that (i) no examples of plant PCD conform to the apoptotic type, (ii) many examples of PCD during plant development agree with the autophagic type, and (iii) that other examples are apparently neither apoptotic nor autophagic.

Apoptosis↗
PubMed2005

Plant programmed cell death and the point of no return.

The point of no return during programmed cell death (PCD) is defined as the step beyond which the cell is irreversibly committed to die. Some plant cells can be saved before this point by inducing the formation of functional chloroplasts. A visibly senescent tissue will then become green again and live for months or years. The mechanism of this reversal is only partially known. The point of no return in fungi and animals is often associated with lack of mitochondrial function. In plant cells that do not regreen, there is no evidence for PCD reversal that results in a long life. It is unclear why chloroplast-containing cells, in contrast to those with only mitochondria, have long lives after PCD reversal.

Animals↗
PubMed2005

Delay of Iris flower senescence by protease inhibitors.

Visible senescence of the flag tepals in Iris x hollandica (cv. Blue Magic) was preceded by a large increase in endoprotease activity. Just before visible senescence about half of total endoprotease activity was apparently due to cysteine proteases, somewhat less than half to serine proteases, with a minor role of metalloproteases. Treatment of isolated tepals with the purported serine protease inhibitors AEBSF [4-(2-aminoethyl)-benzenesulfonyl fluoride] or DFP (diisopropyl-fluorophosphate) prevented the increase in endoprotease activity and considerably delayed or prevented the normal senescence symptoms. The specific cysteine protease-specific E-64d reduced maximum endoprotease activity by 30%, but had no effect on the time to visible senescence. Zinc chloride and aprotinin reduced maximum endoprotease activity by c. 50 and 40%, respectively, and slightly delayed visible senescence. A proteasome inhibitor (Z-leu-leu-Nva-H) slightly delayed tepal senescence, which indicates that protein degradation in the proteasome may play a role in induction of the visible senescence symptoms. It is concluded that visible senescence is preceded by large-scale protein degradation, which is apparently mainly due to cysteine- and serine protease activity, and that two (unspecific) inhibitors of serine proteases considerably delay the senescence symptoms.

Flowers↗
PubMed2004

Senescence and programmed cell death: substance or semantics?

The terms senescence and programmed cell death (PCD) have led to some confusion. Senescence as visibly observed in, for example, leaf yellowing and petal wilting, has often been taken to be synonymous with the programmed death of the constituent cells. PCD also obviously refers to cells, which show a programme leading to their death. Some scientists noted that leaf yellowing, if it has not gone too far, can be reversed. They suggested calling leaf yellowing, before the point of no return, 'senescence' and the process after it 'PCD'. However, this runs into several problems. It is counter to the historical definitions of senescence, both in animal and plant science, which stipulate that senescence is programmed and directly ends in death. It would also mean that only leaves and shoots show senescence, whereas several other plant parts, where reversal has not (yet) been shown, have no senescence, but only PCD. This conflicts with ordinary usage (as in root and flower senescence). Moreover, a programme can be reversible and therefore it is not counter to logic to regard the cell death programme as potentially reversible. In green leaf cells a decision to die, in a programmed way, has been taken, in principle, before the cells start to remobilize their contents (that is, before visible yellowing) and only rarely is this decision reversed. According to the arguments developed here there are no good reasons to separate a senescence phase and a subsequent PCD phase. Rather, it is asserted, senescence in cells is the same as PCD and the two are fully synchronous.

Aging↗
PubMed2004

Daffodil flowers delay senescence in cut Iris flowers.

Visible symptoms of tepal senescence in cut Iris x hollandica (cv. Blue Magic) flowers were delayed by placing one cut daffodil flower (Narcissus pseudonarcissus, cv. Carlton) in the same vase. Addition of mucilage, exuded by daffodil stems, to the vase water had the same effect as the flowering daffodil stem. The active compound in the mucilage was identified as narciclasine (using LC/MS, GC/MS, 1H and 13C-NMR, and comparison with an authentic sample of narciclasine). The delay of senescence, either by mucilage or purified narciclasine, was correlated with a delayed increase in protease activity, and with a considerable reduction of maximum protease activity. Narciclasine did not affect in vitro protease activity, but is known to inhibit protein synthesis at the ribosomal level. Its effects on senescence and protease activity were similar to those of cycloheximide (CHX), another inhibitor of protein synthesis, but the effective narciclasine concentration was about 100 times lower than that of CHX. It is concluded that the delay of Iris tepal senescence by daffodil stems is due to narciclasine in daffodil mucilage, which apparently inhibits the synthesis of proteins involved in senescence.

Adhesives↗
PubMed2003

Flower opening and closure: a review.

Flower opening and closure are traits of a reproductive syndrome, as it allows pollen removal and/or pollination. Various types of opening can be distinguished such as nocturnal and diurnal and single or repetitive. Opening is generally due to cell expansion. Osmotic solute levels increase by the conversion of polysaccharides (starch or fructan) to monosaccharides, and/or the uptake of sugars from the apoplast. Repeated opening and closure movements are often brought about by differential elongation. In tulip petals, for example, the upper and lower sides of the mesophyll exhibit a 10 degrees C difference in optimum temperature for elongation growth, resulting in opening in the morning and closure in the evening. Opening and closure in several other species is regulated by changes in light intensity and, in some species with nocturnal opening, by an increase in relative humidity. A minimum duration of darkness and light are usually required for opening and closure, respectively, in flowers that open during the day. Both phytochrome and a blue light receptor seem involved in light perception. In some species, opening and closure are regulated by an endogenous rhythm, which, in all cases investigated, can be reset by changes from dark to light and/or light to dark. So far, Arabidopsis mutants have not been used to investigate the timing of flower opening and closure. As its flowers open and close in a circadian fashion, several mutants that are involved in the circadian clock and its light input may help to provide an insight into this type of flower opening. The co-ordination of processes culminating in synchronized flower opening is, in many species, highly intricate. The complex control by endogenous and exogenous factors sets flower opening and closure apart from most other growth processes.

Circadian Rhythm↗
PubMed2002

Does ethylene treatment mimic the effects of pollination on floral lifespan and attractiveness?

In some species pollination may result in rapid changes in perianth colour and form (petal senescence and abscission, flower closure), rendering the flowers less attractive to pollinators. It has been suggested that this effect is mediated by ethylene. Flowers from about 200 species and 50 families were exposed to ethylene (3 ppm for 24 h at 20 degrees C). The effects on petal senescence and abscission have been described previously. Flower closure and perianth colour changes were generally ethylene-sensitive, but responses showed no consistency within families. Several flowers known to respond to pollination by rapid cessation of attractiveness were also exposed to ethylene: this produced the same effect as pollination, both on flower colour and form. Species that respond to pollination by changing flower form or colour were found exclusively in families in which the species are generally ethylene-sensitive (with regard to changes in perianth form and colour). However, several families are generally ethylene-sensitive but contain no species reported to respond to pollination.

Apoptosis↗
PubMed2002

Effect of ethylene on flower abscission: a survey.

The effect of ethylene on flower abscission was investigated in monocotyledons and eudicotyledons, in about 300 species from 50 families. In all species studied except Cymbidium, flower abscission was highly sensitive to ethylene. Flower fall was not consistent among the species in any family studied. It also showed no relationship with petal senescence or abscission, nor with petal colour changes or flower closure. Results suggest that flower abscission is generally mediated by endogenous ethylene, but that some exceptional ethylene-insensitive abscission occurs in the Orchidaceae.

Ethylenes↗