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Biomedical subjects

P C Sijmons

Publications and source records attributed to P C Sijmons.

10 recordsLinked to original sources
PubMed2000

The HIC signalling pathway links CO2 perception to stomatal development.

Stomatal pores on the leaf surface control both the uptake of CO2 for photosynthesis and the loss of water during transpiration. Since the industrial revolution, decreases in stomatal numbers in parallel with increases in atmospheric CO2 concentration have provided evidence of plant responses to changes in CO2 levels caused by human activity. This inverse correlation between stomatal density and CO2 concentration also holds for fossil material from the past 400 million years and has provided clues to the causes of global extinction events. Here we report the identification of the Arabidopsis gene HIC (for high carbon dioxide), which encodes a negative regulator of stomatal development that responds to CO2 concentration. This gene encodes a putative 3-keto acyl coenzyme A synthase--an enzyme involved in the synthesis of very-long-chain fatty acids. Mutant hic plants exhibit up to a 42% increase in stomatal density in response to a doubling of CO2. Our results identify a gene involved in the signal transduction pathway responsible for controlling stomatal numbers at elevated CO2.

Algal Proteins↗
PubMed1997

Regulatory sequences of Arabidopsis drive reporter gene expression in nematode feeding structures.

In the quest for plant regulatory sequences capable of driving nematode-triggered effector gene expression in feeding structures, we show that promoter tagging is a valuable tool. A large collection of transgenic Arabidopsis plants was generated. They were transformed with a beta-glucuronidase gene functioning as a promoter tag. Three T-DNA constructs, pGV1047, p delta gusBin19, and pMOG553, were used. Early responses to nematode invasion were of primary interest. Six lines exhibiting beta-glucuronidase activity in syncytia induced by the beet cyst nematode were studied. Reporter gene activation was also identified in galls induced by root knot and ectoparasitic nematodes. Time-course studies revealed that all six tags were differentially activated during the development of the feeding structure. T-DNA-flanking regions responsible for the observed responses after nematode infection were isolated and characterized for promoter activity.

Animals↗
PubMed1993

Differential gene expression in nematode-induced feeding structures of transgenic plants harbouring promoter-gusA fusion constructs.

Sedentary plant-parasitic nematodes are able to induce specialized feeding structures in the root system of their host plants by triggering a series of dramatic cellular responses. These changes presumably are accompanied by a reprogramming of gene expression. To monitor such changes, a variety of promoter-gusA fusion constructs were introduced into Arabidopsis and tobacco. Transgenic plants were analysed histochemically for GUS activity in the nematode feeding structures after infection with either Heterodera schachtii or Meloidogyne incognita. Promoters of the Cauliflower Mosaic Virus 35S gene, the bacterial nopaline synthase, rooting loci (rol) and T-cyt genes and the plant-derived phenylalanine ammonia-lyase I gene, which are highly active in non-infected roots, were all downregulated in the feeding structures as indicated by the strong decrease of GUS activity inside these structures. Less stringent downregulation was observed with chimeric gusA fusion constructs harbouring truncated rolB and rolC promoter sequences. Similar observations were made with transgenic Arabidopsis lines that carried randomly integrated promoterless gusA constructs to identify regulatory sequences in the plant genome. Most of the lines that were selected for expression in the root vascular cylinder demonstrated local downregulation in feeding structures after infection with H. schachtii. The reverse pattern of GUS activity, a blue feeding structure amidst unstained root cells, was also found in several lines. However, GUS activity that was entirely specific for the feeding structures was not observed. Our data show that the expression of a large number of genes is influenced during the development of the nematode feeding structures.

Animals↗
PubMed1992

Production of active Bacillus licheniformis alpha-amylase in tobacco and its application in starch liquefaction.

As a first example of the feasibility of producing industrial bulk enzymes in plants, we have expressed Bacillus licheniformis alpha-amylase in transgenic tobacco, and applied the seeds directly in starch liquification. The enzyme was properly secreted into the intercellular space, and maximum expression levels of about 0.3% of total soluble protein were obtained. No apparent effect of the presence of the enzyme on plant phenotype was observed. The molecular weight of the enzyme produced in tobacco was around 64 kD. The difference, compared to 55.2 kD for the bacterial enzyme, was found to result from complex-type carbohydrate chains attached to the protein. Application studies on the liquefaction of starch were done with transgenic seeds containing the recombinant alpha-amylase. The resulting hydrolysis products were virtually identical with those obtained from degradation with alpha-amylase from Bacillus licheniformis.

Bacillus↗
PubMed1990

Production of correctly processed human serum albumin in transgenic plants.

We have used a modified CaMV 35S promoter to direct the expression of chimaeric genes encoding human serum albumin (HSA) in transgenic potato and tobacco plants. To secrete the protein, either the human prepro-sequence or the signal sequence from the extracellular tobacco protein PR-S was used. We demonstrate secretion of HSA with both types of signal sequences in transgenic leaf tissue and in suspension cultures. HSA produced in transgenic potato plants was purified to chromatographic homogeneity. N-terminal amino acid sequence analysis revealed that the processing of the precursor protein was dependent on the type of signal sequence. Expression of the human preproHSA gene lead to partial processing of the precursor and secretion of proHSA. Fusion of HSA to the plant PR-S presequence resulted in cleavage of the presequence at its natural site and secretion of correctly processed HSA that is indistinguishable from the authentic human protein.

Amino Acid Sequence↗
PubMed1987

Isolation and composition of the constitutive agglutinins from haploid Saccharomyces cerevisiae cells.

Sex-specific agglutinins from the cell surface of haploid cells of Saccharomyces cerevisiae (X2180, mta and mt alpha) were purified and analysed. The constitutive agglutinin from mta cells was extractable with 3 mM dithiothreitol. It was shown to be a glycoprotein (3% mannose) with an apparent Mr of 43,000 based on gel filtration, but in SDS-PAGE it behaved as a much smaller molecule (Mr between 18,000 and 26,000). About one in three amino acids was a hydroxyamino acid. Its biological activity was resistant to boiling for 1 h, but sensitive to pronase. Intact mt alpha cells retained their agglutinability in the presence of dithiothreitol but limited trypsinizing released a biologically active agglutinin fragment. It had an apparent Mr of 320,000 (gel filtration). When analysed by SDS-PAGE, a single diffuse band with an apparent Mr of 225,000 was observed. The protein was 94% (w/w) mannose with a trace of N-acetyl glucosamine. Its biological activity was almost completely lost after boiling for 1 h. Both agglutinins behaved as monovalent molecules and specifically inhibited the biological activity of both noninduced and pheromone-induced cells. Pheromone treatment of mta cells resulted in an apparent 32-fold increase in agglutinin activity at the cell surface, whereas pheromone treatment of mt alpha cells only doubled the apparent agglutinin activity.

Agglutinins↗
PubMed1985

Iron Deficiency Decreases Suberization in Bean Roots through a Decrease in Suberin-Specific Peroxidase Activity.

The suberin content of young root parts of iron-deficient and iron-sufficient Phaseolus vulgaris L. cv Prélude was determined. The aliphatic components that could be released from suberin-enriched fractions by LiAID(4) depolymerization were identified by gas chromatography-mass spectrometry. In the normal roots, the major aliphatic components were omega-hydroxy acids and dicarboxylic acids in which saturated C(16) and monounsaturated C(18) were the dominant homologues. Iron-deficient bean roots contained only 11% of the aliphatic components of suberin found in control roots although the relative composition of the constituents was not significantly affected by iron deficiency. Analysis of the aromatic components of the suberin polymer that could be released by alkaline nitrobenzene oxidation of bean root samples showed a 95% decrease in p-hydroxybenzaldehyde, vanillin, and syringaldehyde under iron-deficient conditions. The inhibition of suberin synthesis in bean roots was not due to a decrease in Fe-dependent omega-hydroxylase activity since normal omega-hydroxylation could be demonstrated, both in vitro with microsomal preparations and in situ by labeling of omega-hydroxy and dicarboxylic acids with [(14)C]acetate. The level of the isozyme of peroxidase that is specifically associated with suberization was suppressed by iron deficiency to 25% of that found in control roots. None of the other extracted isozymes of peroxidase was affected by the iron nutritional status. The activity of the suberin-associated peroxidase was restored within 3 to 4 days after application of iron to the growth medium. The results suggest that, in bean roots, iron deficiency causes inhibition of suberization by causing a decrease in the level of isoperoxidase activity which is required for polymerization of the aromatic domains of suberin, while the ability to synthesize the aliphatic components of the suberin polymer is not impaired.

Journal Article↗
PubMed1984

Cytosolic NADPH is the electron donor for extracellular fe reduction in iron-deficient bean roots.

Pyridine nucleotides were determined in lateral roots of iron-deficient and iron-sufficient Phaseolus vulgaris L. cv Prelude. In iron-deficient plants, total NADP per gram fresh weight and the NADPH/NADP(+) ratio were twice the values found in iron-sufficient plants. The NADPH/NADP(+) ratio in iron-deficient plants was considerably lowered after a 2 minute incubation in 1 millimolar ferricyanide. Total NAD was not influenced by growth conditions and was mainly present in oxidized form.These results indicate that NADPH is the electron donor for the high Fe(III) reduction activity found in iron-deficient roots, a process that is part of the Fe-uptake mechanism.

Journal Article↗
PubMed1984

Depolarization of Cell Membrane Potential during Trans-Plasma Membrane Electron Transfer to Extracellular Electron Acceptors in Iron-Deficient Roots of Phaseolus vulgaris L.

Transfer of electrons from the cytosol of bean (Phaseolus vulgaris L.) root cells to extracellular acceptors such as ferricyanide and Fe(III)EDTA causes a rapid depolarization of the membrane potential. This effect is most pronounced (30-40 millivolts) with root cells of Fe-deficient plants, which have an increased capacity to reduce extracellular ferric salts. Ferrocyanide has no effect. In the state of ferricyanide reduction, H(+) (1H(+)/2 electrons) and K(+) ions are excreted. The reduction of extracellular ferric salts by roots of Fe-deficient bean plants is driven by cellular NADPH (Sijmons, van den Briel, Bienfait 1984 Plant Physiol 75: 219-221). From this and from the membrane potential depolarization, we conclude that trans-plasma membrane electron transfer from NADPH is the primary process in the reduction of extracellular ferric salts.

Journal Article↗