Antagonistic action of low-fluence and high-irradiance modes of response of phytochrome on germination and beta-mannanase activity in Datura ferox seeds.
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Seed germination is often induced by a pulse of red light perceived by phytochrome and cancelled by a subsequent pulse of far-red light. When the pulse of red light is followed by several hours of darkness, a pulse of far-red light is no longer effective and prolonged far-red is necessary to block germination. The aim was to investigate whether the red light pulse and prolonged far-red light act on the same or different processes during germination of Datura ferox seeds. Forty-five hours after the inductive red light pulse, germination could not be blocked by one pulse or six hourly pulses of far-red light, but was significantly reduced by 6 h of continuous far-red light. The pulse of red light increased embryo growth potential and the activities of beta-mannanase and beta-mannosidase extracted from the micropylar region of the endosperm. Continuous far-red light had no effect on embryo growth potential or beta-mannosidase activity, but severely reduced the activity of beta-mannanase. The effect of far-red light had the features of a high-irradiance response of phytochrome. Both germination and beta-mannanase activity were restored by a pulse of red light given after the end of the continuous far-red treatment. It is concluded that the low-fluence response and the high-irradiance response modes of phytochrome have antagonistic effects on seed germination and that the control of beta-mannanase activity is one process where this antagonism is established. (+info)
The distinct disease phenotypes of the common and yellow vein strains of Tomato golden mosaic virus are determined by nucleotide differences in the 3'-terminal region of the gene encoding the movement protein.
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In Nicotiana benthamiana, the common strain of the bipartite geminivirus Tomato golden mosaic virus (csTGMV) induces extensive chlorosis whereas the yellow vein strain (yvTGMV) produces veinal chlorosis on systemically infected leaves. In Datura stramonium, csTGMV produces leaf distortion and a severe chlorotic mosaic whereas yvTGMV produces only small chlorotic lesions on systemically infected leaves. Genetic recombination and site-directed mutagenesis studies using infectious clones of csTGMV and yvTGMV have identified a role in symptom production for the gene encoding the movement protein (MP). The MP amino acid at position 272, either valine (csTGMV) or isoleucine (yvTGMV), influenced symptoms in both hosts by inducing an intermediate phenotype when exchanged between the two strains. Exchange of an additional strain-specific MP amino acid at position 288, either glutamine (csTGMV) or lysine (yvTGMV), resulted in the change of symptom phenotype to that of the other strain. In situ hybridization analysis in N. benthamiana demonstrated that there was no qualitative difference in the tissue distribution of the two strains although csTGMV accumulated in higher amounts, suggesting that the efficiency of virus movement rather than distinct differences in tissue specificity of the strains is responsible for the symptom phenotypes. (+info)
Cymbidium ringspot tombusvirus coat protein coding sequence acts as an avirulent RNA.
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Avirulent genes either directly or indirectly produce elicitors that are recognized by specific receptors of plant resistance genes, leading to the induction of host defense responses such as hypersensitive reaction (HR). HR is characterized by the development of a necrotic lesion at the site of infection which results in confinement of the invader to this area. Artificial chimeras and mutants of cymbidium ringspot (CymRSV) and the pepper isolate of tomato bushy stunt (TBSV-P) tombusviruses were used to determine viral factors involved in the HR resistance phenotype of Datura stramonium upon infection with CymRSV. A series of constructs carrying deletions and frameshifts of the CymRSV coat protein (CP) undoubtedly clarified that an 860-nucleotide (nt)-long RNA sequence in the CymRSV CP coding region (between nt 2666 and 3526) is the elicitor of a very rapid HR-like response of D. stramonium which limits the virus spread. This finding provides the first evidence that an untranslatable RNA can trigger an HR-like resistance response in virus-infected plants. The effectiveness of the resistance response might indicate that other nonhost resistance could also be due to RNA-mediated HR. It is an appealing explanation that RNA-mediated HR has evolved as an alternative defense strategy against RNA viruses. (+info)
Polyamine metabolism and osmotic stress. I. Relation to protoplast viability.
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Cereal leaves subjected to the osmotica routinely used for protoplast isolation show a rapid increase in arginine decarboxylase activity, a massive accumulation of putrescine, and slow conversion of putrescine to the higher polyamines, spermidine and spermine (HE Flores, AW Galston 1984 Plant Physiol 75: 102). Mesophyll protoplasts from these leaves, which have a high putrescine:polyamine ratio, do not undergo sustained division. By contrast, in Nicotiana, Capsicum, Datura, Trigonella, and Vigna, dicot genera that readily regenerate plants from mesophyll protoplasts, the response of leaves to osmotic stress is opposite to that in cereals. Putrescine titer as well as arginine and ornithine decarboxylase activities decline in these osmotically stressed dicot leaves, while spermidine and spermine titers increase. Thus, the putrescine:polyamine ratio in Vigna protoplasts, which divide readily, is 4-fold lower than in oat protoplasts, which divide poorly. We suggest that this differing response of polyamine metabolism to osmotic stress may account in part for the failure of cereal mesophyll protoplasts to develop readily in vitro. (+info)
Biogenesis of T pili in Agrobacterium tumefaciens requires precise VirB2 propilin cleavage and cyclization.
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VirB2 propilin is processed by the removal of a 47-amino-acid signal peptide to generate a 74-amino-acid peptide product in both Escherichia coli and Agrobacterium tumefaciens. The cleaved VirB2 protein is further cyclized to form the T pilin in A. tumefaciens but not in E. coli. Mutations in the signal peptidase cleavage sequence of VirB2 propilin cause the formation of aberrant T pilin and also severely attenuate virulence. No T pilus was observed in these mutants. The potential role of the exact VirB2 propilin cleavage and cyclization in T pilus biogenesis and virulence is discussed. (+info)
Inhibition of proliferation and induction of differentiation of glioma cells with Datura stramonium agglutinin.
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We found that a lectin, Datura stramonium agglutinin, induced irreversible differentiation in C6 glioma cells. The differentiated cells had long processes, a low rate of proliferation and a high content of glial fibrillary acidic protein. When the medium was replaced with Datura stramonium agglutinin-free medium after 1 h, cell proliferation continued to be inhibited. Experiments with several other lectins indicated that both recognition of linear N-acetyllactosamine repeats and recognition of multiantennary units of cell-surface glycans were required for the inhibition of C6 proliferation. Proliferation of four human glial tumour cells was also inhibited by Datura stramonium agglutinin. Further, these differentiated human glial tumour cells had long processes and a high content of glial fibrillary acidic protein similar to differentiated C6 glioma cells. Taken together, these observations suggest that Datura stramonium agglutinin may be useful as a new therapy for treating glioma without side effects. (+info)
Prostaglandin D2 generation by rat peritoneal mast cells stimulated with Datura stramonium agglutinin and its inhibition by haptenic sugar and wheat germ agglutinin.
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The production of prostaglandin D2 (PGD2) by rat peritoneal mast cells incubated with N-acetyl glucosamine (GlcNAc) oligomer-specific Datura stramonium agglutinin (DSA) for 10 min in the presence of 0.3 mM Ca2+ was examined. Previously, our group reported that the incubation of rat mast cells with DSA (5 - 100 microg/ml) under similar conditions resulted in a calcium influx and histamine release via a pertussis toxin-sensitive G-protein pathway of the mast cells, and the histamine release was inhibited by haptenic sugar chitooligosaccharides or GlcNAc-specific lectin wheat germ agglutinin (WGA) (K. Matsuda et al., Jpn J Pharmacol 66, 195 - 204 (1994)). DSA (5 - 100 microg/ml) dose-dependently stimulated the mast cells to generate PGD2. Chitooligosaccharides (1% w/v) and WGA (100 microg/ml) inhibited the production of PGD2 induced by 100 microg/ml of DSA, suggesting that the effect of DSA is sugar-specific. A prostaglandin G/H synthase inhibitor NS-398 (N-[cyclohexyloxy-4-nitrophenyl] methanesulfonamide) (10 microM) inhibited the formation of PGD2 induced by DSA (20 microg/ml). These results suggest that the binding of DSA to the corresponding sugar residues on the mast cell surface mediates the signaling of the prostaglandin G/H synthase pathway. (+info)
Polyamine homeostasis in transgenic plants overexpressing ornithine decarboxylase includes ornithine limitation.
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It was reported recently that overexpression of human ornithine decarboxylase (ODC) cDNA in transgenic rice plants resulted in increased steady-state concentration of polyamines, i.e., enough biosynthetic control is invested at this step to enable adjustment of polyamine levels. To investigate critically whether constitutive overexpression of ODC is sufficient to control steady-state polyamine levels, we expressed an ODC cDNA from Datura stramonium in transgenic tobacco plants. Transgenic progeny of self-fertilised primary transformants exhibited increases in ODC activity of 25-fold in leaves and 5-fold in flower buds. However, the increase in putrescine levels was only 1.5- to 2.1-fold in leaves and 1.1- to 1.3-fold in flower buds. Emphatically, no changes to spermidine or spermine steady-state levels or to soluble or insoluble hydroxycinnamic acid-conjugated polyamines were observed. Ornithine feeding to cell suspension cultures derived from the transgenic plants indicated that putrescine accumulation was limited in part by ornithine availability. These results demonstrate that a large increase in the capacity of the tobacco plants to decarboxylate ornithine does not result in a comparable increase in the level of free or conjugated polyamines. Plant polyamine homeostatic mechanisms efficiently accommodate increased ODC activity, suggesting that polyamine biosynthetic control is invested at multiple interdependent steps. (+info)