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991.
992.
Regulation of photosynthesis during Arabidopsis leaf development in continuous light 总被引:7,自引:0,他引:7
Previous investigations in our laboratory have shown that leaf developmental programming in tobacco is regulated by source
strength. One hypothesis to explain how source strength is perceived is that hexokinase acts as a sensor of carbohydrate flux
to regulate the expression of photosynthetic genes, possibly as a result of sucrose cycling through acid invertase and hexokinase.
We have turned to Arabidopsis as a model system to study leaf development and have examined various photosynthetic parameters during the ontogeny of a
single leaf on the Arabidopsis rosette grown in continuous light. We found that photosynthetic rates, photosynthetic gene expression, pigment contents and
total protein amounts attain peak levels early in the expansion phase of development, then decline progressively as development
proceeds. In contrast, the flux of 14CO2 into hexoses increases modestly until full expansion is attained, then falls in the fully expanded leaf. Partitioning of
carbon into hexoses versus sucrose increases until full expansion is attained, then falls. The in vitro activities of hexokinase, vacuolar acid invertase, and cell wall acid invertase do not change until the late stages of senescence,
when they increase markedly. At this time there are also dramatic increases in hexose pool sizes and in senescence-associated
gene (SAG) expression. Taken together, our results suggest that invertase and hexokinase activities do not control the partitioning
of label into hexoses during development. We conclude that our data are not readily compatible with a simple model of leaf
development, whereby alterations in photosynthetic rates are mediated directly by hexose flux or by hexose pool sizes. Yet,
these factors might contribute to the control of gene expression.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
993.
Schiöth HB Bouifrouri AA Rudzish R Muceniece R Watanobe H Wikberg JE Larhammar D 《Regulatory peptides》2002,106(1-3):7-12
The melanocortin 3 and 4 receptors are G-protein-coupled receptors found in the hypothalamus with important role in regulation of the energy balance. In this study, we performed pharmacological comparison of the rat and human melancortin (MC) 3 and MC4 receptors. We transiently expressed the genes for these receptors individually in a mammalian cell line and determined the binding affinities to several MSH peptides. The results showed no major difference between the rat and human MC3 receptors while the rat MC4 receptor had higher affinity to several peptides compared with the human MC4 receptor. NDP-, alpha-, beta-, gamma-MSH, ACTH(1-24), HS014 and MTII had from 5- to 34-fold higher affinity for the rat MC4 receptor, while SHU9119, HS024 and HS028 had similar affinity for both the MC4 receptors. Pharmacological species difference have earlier been reported for the MC1 and MC5 receptors but this is the first report showing important differences between the rat and human MC4 receptors. 相似文献
994.
D'Eon TM Sharoff C Chipkin SR Grow D Ruby BC Braun B 《American journal of physiology. Endocrinology and metabolism》2002,283(5):E1046-E1055
To assess the roles of endogenous estrogen (E2) and progesterone (P4) in regulating exercise carbohydrate use, we used pharmacological suppression and replacement to create three distinct hormonal environments: baseline (B), with E2 and P4 low; estrogen only (E), with E2 high and P4 low; and estrogen/progesterone (E + P), with E2 and P4 high. Blood glucose uptake (R(d)), total carbohydrate oxidation (CHO(ox)), and estimated muscle glycogen utilization (EMGU) were assessed during 60 min of submaximal exercise by use of stable isotope dilution and indirect calorimetry in eight eumenorrheic women. Compared with B (1.26 +/- 0.04 g/min) and E + P (1.27 +/- 0.04 g/min), CHO(ox) was lower with E (1.05 +/- 0.02 g/min). Glucose R(d) tended to be lower with E and E + P relative to B. EMGU was 25% lower with E than with B or E + P. Plasma free fatty acids (FFA) were inversely related to EMGU (r(2) = 0.49). The data suggest that estrogen lowers CHO(ox) by reducing EMGU and glucose R(d). Progesterone increases EMGU but not glucose R(d). The opposing actions of E(2) and P(4) on EMGU may be mediated by their impact on FFA availability or vice versa. 相似文献
995.
Seguin-Devaux C Devaux Y Latger-Cannard V Grosjean S Rochette-Egly C Zannad F Meistelman C Mertes PM Longrois D 《American journal of physiology. Endocrinology and metabolism》2002,283(3):E525-E535
We have previously shown that all-trans retinoic acid (atRA), the active metabolite of vitamin A, enhances the activation of the inducible nitric oxide synthase (NOS II) pathway, a component of innate immunity, in rats in vivo. We investigated the relative contribution of retinoic acid receptor-alpha (RARalpha) and retinoid X receptors (RXRs) to NOS II activation triggered by LPS. Five-day supplementation with 10 mg/kg of either atRA or the RARalpha selective agonist Ro-40-6055, but not with 10 mg/kg of the pan-RXR agonist Ro-25-7386, enhanced the LPS-induced NOS II mRNA, protein expression in liver, and plasma nitrite/nitrate concentration. Both atRA and the RARalpha agonist (but not the RXR agonist) increased the number of peripheral T helper lymphocytes and plasma interferon-gamma concentration. Synergism between retinoids and LPS on NOS II activation within an organ coincided with synergism on interferon regulatory factor-1 mRNA expression but not with the level of expression of the RARalpha protein. These results suggest that, in vivo, atRA activates NOS II through RARalpha and contributes to characterizing the complex effect of retinoids on the host inflammatory/immune response. 相似文献
996.
Ploug M Gårdsvoll H Jørgensen TJ Lønborg Hansen L Danø K 《Biochemical Society transactions》2002,30(2):177-183
The ability to degrade the extracellular matrix by controlled proteolysis is an important property of malignant cancer cells, which enables them to invade the surrounding tissue and to gain access to the circulation by intravasation. One proteolytic system thought to be involved in these processes is urokinase-mediated plasminogen activation. Expression of a glycolipid-anchored receptor for urokinase-type plasminogen activator (uPA) targets this system to the cell surface. This receptor (uPAR) is composed of three homologous modules belonging to the Ly-6/uPAR/alpha-neurotoxin protein domain family. Integrity of the three-domain structure of uPAR is required for maintenance of its sub-nanomolar affinity for uPA, but the functional epitope for this interaction is primarily located in uPAR domain I. Using affinity maturation by combinatorial chemistry, we have recently identified a potent 9-mer peptide antagonist of the uPA-uPAR interaction having a high affinity for uPAR (K(d)< 1 nM). Photoaffinity labelling suggests that this peptide interacts with a composite binding site in uPAR involving both domains I and III. When tested in a chicken chorioallantoic membrane assay that was developed to quantify intravasation of human cells, this antagonist was able to reduce the intravasation of HEp-3 cancer cells by approx. 60%. 相似文献
997.
Koebmann BJ Westerhoff HV Snoep JL Solem C Pedersen MB Nilsson D Michelsen O Jensen PR 《Molecular biology reports》2002,29(1-2):41-45
Using molecular genetics we have introduced uncoupled ATPase activity in two different bacterial species, Escherichia coli and Lactococcus lactis, and determined the elasticities of the growth rate and glycolytic flux towards the intracellular [ATP]/[ADP] ratio. During balanced growth in batch cultures of E. coli the ATP demand was found to have almost full control on the glycolytic flux (FCC=0.96) and the flux could be stimulated by 70%. In contrast to this, in L. lactis the control by ATP demand on the glycolytic flux was close to zero. However, when we used non-growing cells of L. lactis (which have a low glycolytic flux) the ATP demand had a high flux control and the flux could be stimulated more than two fold. We suggest that the extent to which ATP demand controls the glycolytic flux depends on how much excess capacity of glycolysis is present in the cells. 相似文献
998.
999.
Campino S Behrschmidt C Bagot S Guénet JL Cazenave PA Holmberg D Penha-Gonçalves C 《Genomics》2002,79(5):618-620
Here we report on a genome polymorphism survey using 254 microsatellite markers in ten recently wild-derived inbred strains. Allele size analysis showed that the rate of polymorphism of these wild-derived mouse strains when compared with any of the common laboratory strains is on average 79.8%. We found 632 wild-derived alleles that were not present in the common laboratory strains, representing a 61% increase over the genetic variation observed in the laboratory strains. We also found that on average 14.5% of the microsatellite alleles of any given wild-derived inbred strain were unique. Our results indicate that the recently wild-derived mouse strains represent repositories of unique naturally occurring genetic variability and may prove invaluable for the study of complex phenotypes and in the construction of new mouse models of human disease. 相似文献
1000.