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PubMed1996

Helicobacter pylori cytotoxin induces vacuolation of primary human mucosal epithelial cells.

We investigated whether Helicobacter pylori cytotoxin induces vacuolation in primary epithelial cells from normal human mucosa. Epithelial cells purified by enzyme digestion and elutriation were evaluated for vacuolation in a blinded protocol by light and electron microscopy before and after incubation with culture supernatant (CS) from H. pylori 60190, which has vacuolating activity for HeLa cells (Tox+), and isogenic H. pylori mutant 60190-v1, which lacks this activity (Tox-). Primary epithelial cells (>98% pure) exposed to CS from Tox+ H. pylori exhibited marked vacuolation (52% +/- 5% of cells) compared with epithelial cells exposed to either CS from Tox- H. pylori (23% +/- 3.2%) or uninoculated control broth (23% +/- 3.7%) (P < 0.05) by light microscopy, which was confirmed by electron microscopy and antibody inhibition studies. These are the first data to show that H. pylori cytotoxin causes vacuolation of primary human mucosal epithelial cells.

Bacterial Proteins↗

PubMed2026

EndoV does not measurably affect TadA-dependent A-to-I RNA editing in Escherichia coli under exponential-growth conditions in rich medium.

Adenosine-to-inosine (A-to-I) mRNA editing changes the genetic information post-transcriptionally and was only recently reported to occur in bacteria. Here, we examined whether endonuclease V (EndoV; encoded by nfi) cleaves inosine-containing RNAs in vivo and thereby influences the abundance and fate of A-to-I-edited mRNAs in Escherichia coli. We generated an nfi loss-of-function mutant carrying a premature stop codon and performed RNA sequencing alongside the isogenic wild-type strain. We observed that global and site-specific editing occurrence or levels in both mRNAs and tRNAs were indistinguishable between strains. Moreover, overexpression of EndoV did not affect the number of edited sites, motif enrichment, or editing levels compared with a control strain overexpressing mCherry. Our findings suggest that, in contrast to human EndoV, bacterial EndoV does not regulate the steady-state pool of edited mRNAs in E. coli under nutrient-rich, exponential-growth conditions in vivo.IMPORTANCEAdenosine-to-inosine (A-to-I) mRNA editing is an emerging regulatory layer in bacteria, but the factors that act on edited transcripts are largely unknown. Endonuclease V (EndoV) was a prime candidate because it cleaves inosine-containing nucleic acids and can act on inosine-containing RNA in vitro. By combining loss-of-function and overexpression of EndoV with genome-wide RNA editing measurements, we show that EndoV does not measurably influence TadA-dependent A-to-I mRNA editing in Escherichia coli under standard laboratory conditions. This negative result is important because it rules out a natural effector candidate and redirects attention to other bacterial pathways that may process edited RNAs. Our work, therefore, sharpens mechanistic models for bacterial RNA editing and helps focus future searches for its regulators and physiological roles.

Escherichia coli↗

PubMed2000

[Histologic study of experimental spleen transplant in rats].

BACKGROUND: The objective of this paper was to demonstrate that the grafts of cervical splenic transplantation on rats using our experimental model present a normal histological appearance. METHODS: Isogenic consanguineous Lewis rats 12 weeks old and weighing 250 gr. were used. Histological findings of a group of 25 cervical splenic grafts transplanted by means of splinting vascular venous microanastomoses and a group of 25 splenic grafts autotransplanted in the omentum were compared with a control group. The specimens were assigned according to a score of 0 to 4, following Moore's histological criteria. RESULTS: All grafts in transplanted and autotransplanted groups had a score of 3 or 4. Then, all splenic grafts from the transplanted group had histological findings very similar to a normal spleen. In the autotransplantation group, the percentage of grafts with a score 3 (60%) was superior to the transplantation group (46%). However, the transplantation group presented a percentage of score 4 (54%), superior to the autotransplantation group (40%). CONCLUSIONS: In our study all grafts from the cervical spleen transplantation group had histological findings very similar to a normal spleen. The percentage of spleens with histological normality in the transplantation group was superior to the autotransplantation group. However, there was no statistical significance.

Animals↗

PubMed2003

[Induction of MGE 412 transposition in an isogenic strain of Drosophila melanogaster by different doses of ethanol fumes].

The effect of treatment of males from an isogenic Drosophila melanogaster strain by limiting doses of ethanol fumes on transpositions of MGE 412 was examined. Validity of the phenomenon of transposition induction was demonstrated. We estimated rates of induced transposition (approximately 10(-2) events per site, per sperm, per generation versus < 10(-3) in control) and showed dose dependence of the rate on the exposure time of the males to ethanol fumes. Experiments with alcohol treatment at limiting doses must end either in death of the individuals or bursts of genetic variability in their progeny. In terms of genetics of an individual, this may mean loss of vital hereditary basis followed by mass degradation of the progeny of the "hard drinkers." In terms of populations genetics, this mode of MGE transposition induction can rapidly create a burst of novel genetic variation, which, apart of great losses, may generate a number of advantageous individuals, i.e., be significant for population survival in new, stressful environments.

Animals↗

PubMed1983

Hypogastrinemia in streptozotocin diabetes with islet transplantation--reconstitution.

Gastrin is present in normal mammalian pancreatic islets, as well as in the antrum and duodenum. Serum gastrin levels are responsive to many physiologic and pharmacologic factors including hyperglycemia, somatostatin, and glucagon. To evaluate the effects of streptozotocin diabetes and islet transplantation on gastrin homeostasis, young, adult, male Lewis rats underwent streptozotocin diabetes alone (N = 14), diabetes plus intraperitoneal islet isografts (N = 22), or sham operation alone (N = 18). Streptozotocin reduced fasting gastrin immunoreactivity (107 pg/ml +/- 26 mean +/- SEM) compared to controls (256 pg/ml +/- 31) (P less than 0.001). Islet isotransplantation resulted in restoration of fasting gastrin immunoreactivity (230 pg/ml +/- 19) to levels significantly greater than diabetics (P less than 0.001) and comparable to control animals (P = NS). Normalization of serum gastrin levels occurred within one month of transplantation and persisted for up to 14 months. In addition, media from cultures of 4/7 dispersed neonatal rat pancreas cultures contained gastrin immunoreactivity. Streptozotocin diabetes produces hypogastrinemia; intraperitoneal islet isotransplantation normalizes fasting gastrin immunoreactivity. Rat islet culture medium contains gastrin-like immunoreactivity. Pancreatic islets would appear to produce or control a portion of circulating gastrin immunoreactivity.

Animals↗

PubMed1980

[Morphological changes in the transplanted rat kidney under conditions of minor and major histocompatibility differences between donor and recipient].

Morphological changes in transplanted kidney were studied in 4 groups of rats with different histocompatibility differences between donor and recipient: 1. syngenetic differences, 2. differences in the main histocompatibility system H-1, 3. differences in the H-1 as well as in the subsidiary non-H-1 systems, 4. differences in the non-H-1 systems. -- In all the kidneys transplanted from a newly developed congenetic strain BP.1N to inbred rats of the BN strain (with differences in the non-H-1 systems) rejection developed in 2 to 3 weeks with manifestations of giant-cell interstitial nephritis with gradual destruction and phagocytosis of cortical tubules probably due to the production of antibodies against the basal membranes of tubules. -- In the paralel group with differences in the non-H-1 systems of BP into BN-1B, destroyed after 30 days, there were -- in addition to moderate acute rejection -- hypercellular glomerules with electrodense deposits in the mesangium seen as a manifestation of immuno-complex glomerulonephritis. Analogical glomerular changes without rejection were also fond in a control group of longer surviving syngenetic rats.

Animals↗

PubMed1999

Regulation of virus release by the macrophage-tropic human immunodeficiency virus type 1 AD8 isolate is redundant and can be controlled by either Vpu or Env.

The human immunodeficiency virus type 1 (HIV-1) Vpu and Env proteins are expressed from a bicistronic mRNA. To address the biological significance of the coordinated expression of vpu and env, we compared the relative effects on particle release of HIV-1 isolates containing an intact vpu gene or carrying point mutations in its initiation codon or internal deletions, respectively. We found that the primary AD8 isolate, which is unable to express vpu due to a mutation in its translation initiation codon, was able to replicate in primary macrophages and peripheral blood mononuclear cells with efficiency similar to that of an isogenic variant expressing Vpu. Interestingly, AD8 lacking a vpu initiation codon produced higher levels of Env protein than its Vpu-expressing isogenic variant. In contrast, disabling Vpu without removing the vpu initiation codon did not alter Env expression but significantly reduced virus production. AD8 Env when provided in trans was capable of enhancing release not only of AD8 particles but also of viruses of the T-cell-tropic NL4-3 isolate. We conclude that AD8 Env encodes a Vpu-like activity similar to that previously reported for HIV-2 Env proteins and is thus able to augment virus secretion. When expressed at elevated levels, i.e., following mutation of the vpu initiation codon, AD8 Env was able to compensate for the lack of Vpu and thereby ensure efficient virus release. Thus, the ability to regulate virus release is redundant in AD8 and can be controlled by either Vpu or Env. Since Vpu controls several independent functions, including CD4 degradation, our results suggest that some HIV-1 isolates may have evolved a mechanism to regulate Vpu activity without compromising their ability to efficiently replicate in the host cells.

Amino Acid Sequence↗

PubMed2002

Cloning and mapping of genes involved in wheat-leaf rust interaction through gene-expression analysis using chromosome-deleted near-isogenic wheat lines.

Molecular markers on wheat chromosome 6BL were isolated using mRNA differential display. Two wheat isolines inoculated with Puccinia recondita were analysed: Sinvalocho MA line carrying the Lr3 gene for leaf rust resistance on distal chromosome 6BL, and a rust-susceptible derivative of the Sinvalocho MA line with a deletion at the distal end of chromosome 6BL. Comparison of mRNA fingerprinting profiles, obtained from control and rust-inoculated plants, let to the isolation of 34 differentially displayed cDNAs. All these genes, except TaRr16, were up-regulated in the rust-inoculated resistant line. TaRr16 has constitutive expression in the rust-resistant line while no expression was detected in the rust-susceptible line. A number of those cDNAs revealed homology to genes previously identified in other plant-pathogen interactions. Two out of the 34 cDNAs, mapped in the distal part of chromosome 6BL and TaRr16, was genetically linked to the Lr3 gene. DNA sequence differences and differential expression between non-allelic copies of TaRr16, are also reported.

Journal Article↗

PubMed2002

Overexpression of BclXL in a human ovarian carcinoma cell line: paradoxic effects on chemosensitivity in vitro versus in vivo.

The effect of overexpressing the antiapoptotic protein BclXL in a human ovarian carcinoma cell line has been investigated in terms of sensitivity to the 2 major drugs used to treat this disease, paclitaxel and cisplatin. Stable transfection of BclXL into CH1 cells, which are relatively sensitive to cisplatin, resulted in around 2.7-fold higher expression in comparison with empty vector controls. However, this level of overexpression did not result in significant resistance in vitro to paclitaxel or cisplatin at the 50% inhibition level, using either short-term (4-day) growth inhibition or longer term colony-forming assays. By contrast, parallel subcutaneous xenograft models of these isogenic ovarian carcinoma cells in vivo, differing only in BclXL status, showed that this low-level BclXL overexpression conferred significant resistance to both paclitaxel and cisplatin in comparison with parent, nontransfected tumours. Whereas parent non-BclXL transfected tumours were highly responsive, with the disappearance of tumours for at least 50 days post treatment, tumours overexpressing BclXL grew back after 30 and 20 days after treatment with paclitaxel and cisplatin, respectively. These differences in responsiveness to paclitaxel in vivo were not attributable to any significant changes in the delivery of drug to the tumour. These data suggest that the responsiveness of ovarian cancer to paclitaxel and cisplatin in vivo, and therefore perhaps clinically, is influenced by levels of the antiapoptotic protein BclXL. Such effects may be missed in vitro when using short-term growth inhibition or clonogenic assays.

Animals↗

PubMed1997

Influence of ATM function on telomere metabolism.

The ATM gene product, which is defective in the cancer-prone disorder ataxia telangiectasia, has been implicated in mitogenic signal transduction, chromosome condensation, meiotic recombination and cell cycle control. The ATM gene has homology with the TEL1 gene of yeast, mutations of which lead to shortened telomeres. To test the hypothesis that the ATM gene product is involved in telomere metabolism, we examined telomeric associations (TA), telomere length, and telomerase activity in human cells expressing either dominant-negative or complementing fragments of the ATM gene. The phenotype of RKO colorectal tumor cells expressing ATM fragments containing a leucine zipper (LZ) motif mimics that of ataxia telangiectasia (A-T) cells. These transfected RKO cells relative to transfected controls had a higher frequency of cells with TA and shortened telomeres, but no detectable change in telomerase activity. In addition, the percentage of cells with TA after gamma irradiation was higher in the transfected RKO cells with dominant negative activity of the ATM gene, compared to control cells. SV40 transformed fibroblasts derived from an A-T patient and transfected with a complementing carboxyl terminal kinase region of the ATM gene had a reduced frequency of cells with TA, with no effect on the telomere length or telomerase activity. The present studies using isogenic cells with manipulated ATM function demonstrate a role for the ATM gene product in telomere metabolism.

Animals↗

PubMed2001

Actin is ADP-ribosylated by the Salmonella enterica virulence-associated protein SpvB.

The Salmonella enterica virulence-associated protein SpvB was recently shown to contain a carboxy-terminal mono(ADP-ribosyl)transferase domain. We demonstrate here that the catalytic domain of SpvB as well bacterial extracts containing full-length SpvB modifies a 43 kDa protein from macrophage-like J774-A.1 and epithelial MDCK cells as shown by label transfer from [32P]-nicotinamide adenine dinucleotide (NAD) to the 43 kDa protein. When analysed by two-dimensional gel electrophoresis, the same protein was modified in cells infected with S. enterica serovariant Dublin strain SH9325, whereas infection with an isogenic spvB mutant strain did not result in modification. Immunoprecipitation and immunoblotting experiments using SH9325-infected cells identified the modified protein as actin. The isolated catalytic domain of SpvB mediated transfer of 32P from [32P]-NAD to actins from various sources in vitro, whereas isolated eukaryotic control proteins or bacterial proteins were not modified. In an in vitro actin polymerization assay, the isolated catalytic SpvB domain prevented the conversion of G actin into F actin. Microscopic examination of MDCK cells infected with SH9325 revealed morphological changes and loss of filamentous actin content, whereas cells infected with the spvB mutant remained virtually unaffected. We conclude that actin is a target for an SpvB-mediated modification, most probably ADP-ribosylation, and that the modification of G actin interferes with actin polymerization.

ADP Ribose Transferases↗

PubMed2002

Reduced oxidative pentose phosphate pathway flux in recombinant xylose-utilizing Saccharomyces cerevisiae strains improves the ethanol yield from xylose.

In recombinant, xylose-fermenting Saccharomyces cerevisiae, about 30% of the consumed xylose is converted to xylitol. Xylitol production results from a cofactor imbalance, since xylose reductase uses both NADPH and NADH, while xylitol dehydrogenase uses only NAD(+). In this study we increased the ethanol yield and decreased the xylitol yield by lowering the flux through the NADPH-producing pentose phosphate pathway. The pentose phosphate pathway was blocked either by disruption of the GND1 gene, one of the isogenes of 6-phosphogluconate dehydrogenase, or by disruption of the ZWF1 gene, which encodes glucose 6-phosphate dehydrogenase. Decreasing the phosphoglucose isomerase activity by 90% also lowered the pentose phosphate pathway flux. These modifications all resulted in lower xylitol yield and higher ethanol yield than in the control strains. TMB3255, carrying a disruption of ZWF1, gave the highest ethanol yield (0.41 g g(-1)) and the lowest xylitol yield (0.05 g g(-1)) reported for a xylose-fermenting recombinant S. cerevisiae strain, but also an 84% lower xylose consumption rate. The low xylose fermentation rate is probably due to limited NADPH-mediated xylose reduction. Metabolic flux modeling of TMB3255 confirmed that the NADPH-producing pentose phosphate pathway was blocked and that xylose reduction was mediated only by NADH, leading to a lower rate of xylose consumption. These results indicate that xylitol production is strongly connected to the flux through the oxidative part of the pentose phosphate pathway.

Ethanol↗

PubMed1993

Alveolar epithelial injury and pleural empyema in acute P. aeruginosa pneumonia in anesthetized rabbits.

We developed an experimental model of acute Pseudomonas aeruginosa pneumonia in anesthetized ventilated rabbits to determine whether bacterial-induced injury to the alveolar epithelium would occur and the effect of the injury on the pleural space. Dose-response studies established that 10(9) colony-forming units of P. aeruginosa (wild-type strain, PAO-1) were required to injure the epithelial barrier and to cause pleural empyema with exudative pleural effusions that contained both the instilled alveolar protein tracer and P. aeruginosa. We explored the mechanisms of P. aeruginosa-induced lung and pleural injury by using three isogenic bacterial strains to compare several extracellular virulence products. PAO-S21, which carries an insertion mutation in a regulatory gene that prevents the production of exoenzyme S, resulted in no lung or pleural injury. PAO-R1, which carries a deletion in a regulatory gene that controls the production of elastase and alkaline protease, caused the same degree of lung and pleural injury as PAO-1 did. Instillation of PLC-SRN, which has both structural genes encoding phospholipase C activity deleted, resulted in a moderate reduction in alveolar epithelial injury. Although other products may be involved, exoenzyme S and phospholipase C are important in mediating injury to the alveolar epithelial barrier in acute P. aeruginosa pneumonia in rabbits.

Anesthesia↗

PubMed1978

Curing of an R factor from Escherichia coli by hydroxyurea and cytosine arabinoside.

Hydroxyurea (HU) and cytosine arabinoside (Ara-C) eliminate R factor R46 from Escherichia coli strain J5-3. The highest frequency of elimination for both drugs occurred at concentrations and times that produced the lowest survivor levels. 5% of cells were antibiotic-sensitive after 5 h incubation in 5 mg/ml Ara-C, whilst 6 and 7% of the survivors had lost the R factor after 8 and 24 h incubation, respectively in 20 mg/ml HU. The number of survivors began to increase after 5 h incubation in Ara-C, probably due to the inactivation of the drug in the phosphate-buffered medium. All four antibiotic resistances (ampicillin, streptomycin, sulphonamide and tetracycline) mediated by R46 were lost simultaneously and elimination of the whole plasmid was confirmed by conjugation experiments in which the 'cured' cells was shown to be as efficient recipients of R46 as the control R- strain in crosses with E. coli strain J6-2 (R46). No covalently closed circular plasmid DNA was demonstrable in cured cell lines. R+ and R- strains had similar sensitivities to HU but J5-3 R+ was much more sensitive to Ara-C than the isogenic R- strain. It may be concluded that HU eliminates R46 actively whereas although Ara-C may produce some active elimination it acts mainly by selection of R- cells present in the culture.

Culture Media↗

PubMed2002

An antisense oligonucleotide targeted to human Ku86 messenger RNA sensitizes M059K malignant glioma cells to ionizing radiation, bleomycin, and etoposide but not DNA cross-linking agents.

Ku is a heterodimer of M(r) 70,000 and M(r) 86,000 subunits. It binds with strong affinity to DNA ends and is indispensable for nonhomologous DNA end joining (NHEJ) and V(D)J recombination. In this study, we investigated whether down-regulation of the Ku86 gene, by 2'-O-methoxyethyl/uniform phosphorothioate chimeric antisense oligonucleotides (ASOs), increases the sensitivity of the DNA-protein kinase catalytic subunit (PKcs)-proficient human glioma cell line (M059K), and its isogenic DNA-PKcs-deficient counterpart (M059J), to ionizing radiation and anticancer drugs. Transfection of these cell lines with 200 nM Ku86 antisense ASOs was associated with a specific decrease in Ku86 mRNA levels (IC(50) <25 nM; n = 3) and a concomitant rapid decrease (<10% of control) in Ku86 protein expression. Moreover, transfection of M059K cells with Ku86 antisense ASOs markedly increased cell death after treatment with ionizing radiation, bleomycin, and etoposide. However, no sensitization to the DNA cross-linking agents chlorambucil and cisplatin was observed after Ku86 antisense transfection. As expected, transfection of M059J cells with Ku86 antisense ASOs did not result in any sensitization to ionizing radiation, bleomycin, or DNA cross-linking agents, but there was a 2-fold increase in sensitivity to etoposide. Thus, our results indicate that antisense ASOs targeted against Ku86 may increase the efficacy of radiotherapy and DNA-damaging agents in tumor treatment. Furthermore, Ku86 antisense ASOs may be used to create a temporal knockout in different human cell lines to further investigate the biological roles of Ku86.

Antigens, Nuclear↗

PubMed1992

Elimination of the yeast RAD6 ubiquitin conjugase enhances base-pair transitions and G.C----T.A transversions as well as transposition of the Ty element: implications for the control of spontaneous mutation.

The RAD6 gene of the yeast Saccharomyces cerevisiae encodes an enzyme that conjugates ubiquitin to other proteins. Defects in RAD6 confer a mutator phenotype due, in part, to an increased rate of transposition of the yeast Ty element. To further delineate the role of protein ubiquitination in the control of spontaneous mutagenesis in yeast, we have characterized 202 mutations that arose spontaneously in the SUP4-o gene carried on a centromere vector in a RAD6 deletion strain. The resulting mutational spectrum was compared to that for 354 spontaneous SUP4-o mutations isolated in the isogenic wild-type parent. This comparison revealed that the rad6 mutator enhanced the rate of single base-pair substitution, as well as Ty insertion, but did not affect the rates of the other mutational classes detected. Relative to the wild-type parent, Ty inserted at considerably more SUP4-o positions in the rad6 strain with a significantly smaller fraction detected at a transposition hotspot. These findings suggest that, in addition to the rate of transposition, protein ubiquitination might influence the target site specificity of Ty insertion. The increase in the substitution rate accounted for approximately 90% of the rad6 mutator effect but only the two transitions and the G. C----T.A transversion were enhanced. Analysis of the distribution of these events within SUP4-o suggested that the site specificity of the substitutions was influenced by DNA sequence context. Transformation of heteroduplex plasmid DNAs into the two strains demonstrated that the rad6 mutator did not reduce the efficiency of correcting mismatches that could give rise to the transitions or transversion nor did it bias restoration of the mismatches to the incorrect base-pairs. These results are discussed in relation to possible mechanisms that might link ubiquitination of proteins to spontaneous mutation rates.

Base Composition↗

PubMed2003

Biofilm formation by Pseudomonas aeruginosa: role of the C4-HSL cell-to-cell signal and inhibition by azithromycin.

OBJECTIVES: In Pseudomonas aeruginosa, biofilm formation is controlled by a cell-to-cell signalling circuit relying on the secretion of 3-oxo-C12-HSL and C4-HSL. Previous studies suggested that C4-HSL plays no significant role in biofilm formation. However the wild-type PAO1 strain PAO-BI, used as a control in these studies is itself impaired in the production of C4-HSL. We wondered therefore whether the role of C4-HSL in biofilm formation might have been underestimated, and whether azithromycin inhibits biofilm formation by interfering with cell-to-cell signalling. METHODS: We used isogenic mutants of wild-type PAO1 strains PAO-BI and PT5 in a static biofilm model. Biofilm formation was quantified using Crystal Violet staining and exopolysaccharide measurements. RESULTS: Wild-type strain PAO-BI, as a result of its reduced C4-HSL secretion, produced 40% less biofilm compared with the wild-type PAO1 strain PT5. Using isogenic mutants of strain PT5 we have shown that whereas a lasI mutant (deficient in 3-oxo-C12-HSL) produced similar amounts of biofilm to the wild-type, a rhlI mutant (deficient in C4-HSL) produced 70% less biofilm. In the latter strain, biofilm formation could be restored by addition of exogenous C4-HSL. Azithromycin, known to reduce the production of both 3-oxo-C12-HSL and C4-HSL, inhibited biofilm formation of wild-type PT5 by 45%. This inhibition could be reversed by the addition of both cell-to-cell signals. CONCLUSIONS: Our results indicate that C4-HSL also plays a significant role in biofilm formation. Furthermore, we demonstrate the potential of using cell-to-cell signalling blocking agents such as azithromycin to interfere with biofilm formation.

4-Butyrolactone↗

PubMed1989

Effect of Temperature on Gibberellin (GA) Responsiveness and on Endogenous GA(1) Content of Tall and Dwarf Wheat Genotypes.

Near-isogenic wheat (Triticum aestivum L.) lines differing in height-reducing (Rht) alleles were used to investigate the effects of temperature on endogenous gibberellin (GA) levels and seedling growth response to applied GA(3). Sheath and lamina lengths of the first leaf were measured in GA treated and control seedlings, grown at 11, 18, and 25 degrees C, of six Rht genotypes in each of two varietal backgrounds, cv Maris Huntsman and cv April Bearded. Endogenous GA(1) levels in the leaf extension zone of untreated seedlings were determined by gas chromatography-mass spectrometry with a deuterated internal standard in the six Maris Huntsman Rht lines grown at 10 and 25 degrees C. Higher temperature increased leaf length considerably in the tall genotype, less so in the Rht1 and Rht2 genotypes, and had no consistent effect on the Rht1+2, Rht3 and Rht2+3 genotypes. In all genotypes, endogenous GA(1) was higher at 25 degrees C than at 10 degrees C. At 10 degrees C the endogenous GA(1) was at a similar level in all the genotypes (except Rht2+3). At 25 degrees C it increased 1.6-fold in the tall genotype, 3-fold in Rht1 and Rht2, 6-fold in Rht3, and 9-fold in Rht1+2. Likewise, the genotypic differences in leaf length were very conspicuous at 25 degrees C, but were only slight and often unsignificant at 11 degrees C. The response of leaf length to applied GA(3) in the Rht1, Rht2, and Rht1+2 genotypes increased significantly with lowering of temperature. These results suggest the possibility that the temperature effect on leaf elongation is mediated through its effect on the level of endogenous GA(1) and that leaf elongation response to endogenous or applied GAs is restricted by the upper limits set by the different Rht alleles.

Journal Article↗