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84.
Oxygen Requirement and Inhibition of C4
Photosynthesis
: An Analysis of C4 Plants Deficient in the
C3 and C4 Cycles 总被引:2,自引:0,他引:2 下载免费PDF全文
Jo?o P. Maroco Maurice S.B. Ku Peter J. Lea Louisa V. Dever Richard C. Leegood Robert T. Furbank Gerald E. Edwards 《Plant physiology》1998,116(2):823-832
The basis for O2 sensitivity of C4 photosynthesis was evaluated using a C4-cycle-limited mutant of Amaranthus edulis (a phosphoenolpyruvate carboxylase-deficient mutant), and a C3-cycle-limited transformant of Flaveria bidentis (an antisense ribulose-1,5-bisphosphate carboxylase/oxygenase [Rubisco] small subunit transformant). Data obtained with the C4-cycle-limited mutant showed that atmospheric levels of O2 (20 kPa) caused increased inhibition of photosynthesis as a result of higher levels of photorespiration. The optimal O2 partial pressure for photosynthesis was reduced from approximately 5 kPa O2 to 1 to 2 kPa O2, becoming similar to that of C3 plants. Therefore, the higher O2 requirement for optimal C4 photosynthesis is specifically associated with the C4 function. With the Rubisco-limited F. bidentis, there was less inhibition of photosynthesis by supraoptimal levels of O2 than in the wild type. When CO2 fixation by Rubisco is limited, an increase in the CO2 concentration in bundle-sheath cells via the C4 cycle may further reduce the oxygenase activity of Rubisco and decrease the inhibition of photosynthesis by high partial pressures of O2 while increasing CO2 leakage and overcycling of the C4 pathway. These results indicate that in C4 plants the investment in the C3 and C4 cycles must be balanced for maximum efficiency. 相似文献
85.
Louisa V. Dever Mark Pearson Robert J. Ireland Richard C. Leegood Peter J. Lea 《Planta》1998,206(4):649-656
A mutant of Amaranthus edulis (Speg.) lacking activity of the C4 leaf form of NAD-malic enzyme (ME; EC 1.1.1.39) has been isolated. Homozygous mutant (5% wild-type ME activity) and heterozygous
(50% wild-type ME activity) F2 plants were shown to contain both the α and β NAD-ME subunits in similar amounts to those detected in the wild-type leaves.
The rate of photosynthetic CO2 assimilation was reduced in the homozygous mutant to 5% of that observed for the wild-type leaves. Other C4 enzymes were not down-regulated in the mutant plants. There was little difference in photosynthetic rate of the heterozygous
plants compared to the wild-type, suggesting that NAD-ME exerts little control over the rate of C4 photosynthesis, and that in the wild-type the enzyme has a very low control coefficient. The activity loss in the heterozygote
may therefore be compensated by regulatory mechanisms that increase the activity of the enzyme in vivo. Data for bundle-sheath
strands indicated that although the homozygous mutants were able to oxidise malate via the Krebs cycle, they were unable to
convert malate to pyruvate and alanine via NAD-ME.
Received: 2 April 1998 / Accepted: 7 May 1998 相似文献
86.
Daniel Bronder Anthony Tighe Darawalee Wangsa Dali Zong Thomas J. Meyer Ren Wardenaar Paul Minshall Daniela Hirsch Kerstin Heselmeyer-Haddad Louisa Nelson Diana Spierings Joanne C. McGrail Maggie Cam Andr Nussenzweig Floris Foijer Thomas Ried Stephen S. Taylor 《Disease models & mechanisms》2021,14(11)
87.
Sajad Sofi Louisa Williamson Gabrielle L. Turvey Charlotte Scoynes Claire Hirst Jonathan Godwin Neil Brockdorff Justin Ainscough Dawn Coverley 《The Journal of cell biology》2022,221(4)
CIZ1 forms large assemblies at the inactive X chromosome (Xi) in female fibroblasts in an Xist lncRNA-dependent manner and is required for accurate maintenance of polycomb targets genome-wide. Here we address requirements for assembly formation and show that CIZ1 undergoes two direct interactions with Xist, via independent N- and C-terminal domains. Interaction with Xist, assembly at Xi, and complexity of self-assemblies formed in vitro are modulated by two alternatively spliced glutamine-rich prion-like domains (PLD1 and 2). PLD2 is dispensable for accumulation at existing CIZ1–Xi assemblies in wild-type cells but is required in CIZ1-null cells where targeting, assembly, and enrichment for H3K27me3 and H2AK119ub occur de novo. In contrast, PLD1 is required for both de novo assembly and accumulation at preexisting assemblies and, in vitro, drives formation of a stable fibrillar network. Together they impart affinity for RNA and a complex relationship with repeat E of Xist. These data show that alternative splicing of two PLDs modulates CIZ1’s ability to build large RNA–protein assemblies. 相似文献
88.
Frequent simian foamy virus infection in persons occupationally exposed to nonhuman primates 总被引:4,自引:0,他引:4 下载免费PDF全文
Switzer WM Bhullar V Shanmugam V Cong ME Parekh B Lerche NW Yee JL Ely JJ Boneva R Chapman LE Folks TM Heneine W 《Journal of virology》2004,78(6):2780-2789
The recognition that AIDS originated as a zoonosis heightens public health concerns associated with human infection by simian retroviruses endemic in nonhuman primates (NHPs). These retroviruses include simian immunodeficiency virus (SIV), simian T-cell lymphotropic virus (STLV), simian type D retrovirus (SRV), and simian foamy virus (SFV). Although occasional infection with SIV, SRV, or SFV in persons occupationally exposed to NHPs has been reported, the characteristics and significance of these zoonotic infections are not fully defined. Surveillance for simian retroviruses at three research centers and two zoos identified no SIV, SRV, or STLV infection in 187 participants. However, 10 of 187 persons (5.3%) tested positive for SFV antibodies by Western blot (WB) analysis. Eight of the 10 were males, and 3 of the 10 worked at zoos. SFV integrase gene (int) and gag sequences were PCR amplified from the peripheral blood lymphocytes available from 9 of the 10 persons. Phylogenetic analysis showed SFV infection originating from chimpanzees (n = 8) and baboons (n = 1). SFV seropositivity for periods of 8 to 26 years (median, 22 years) was documented for six workers for whom archived serum samples were available, demonstrating long-standing SFV infection. All 10 persons reported general good health, and secondary transmission of SFV was not observed in three wives available for WB and PCR testing. Additional phylogenetic analysis of int and gag sequences provided the first direct evidence identifying the source chimpanzees of the SFV infection in two workers. This study documents more frequent infection with SFV than with other simian retroviruses in persons working with NHPs and provides important information on the natural history and species origin of these infections. Our data highlight the importance of studies to better define the public health implications of zoonotic SFV infections. 相似文献
89.
Insulin has been shown to acutely regulate hepatic apolipoprotein B (apoB) secretion at both translational and post-translational levels; however, mechanisms of apoB mRNA translational control are largely unknown. Recent studies of apoB untranslated regions (UTRs) revealed a potentially important role for cis-trans interactions at the 5' and 3' UTRs. In the present paper, deletion constructs of the UTR regions of apoB revealed that the 5' UTR was necessary and sufficient for insulin to inhibit synthesis of apoB15. Metabolic radiolabeling and in vitro translation experiments in the presence of protease inhibitors confirmed that the effect of insulin on the apoB 5' UTR was translational in nature. Using the nondenaturing electrophoretic mobility shift assay (EMSA), protein-RNA complexes were detected binding to the apoB 5' and 3' UTRs. Denaturing EMSA identified a 110-kDa protein interacting at the 5' UTR. Nondenaturing EMSA determined that insulin altered binding of large protein complexes to the 5' UTR. Binding specificity was determined by competition with both specific and nonspecific competitors. Insulin treatment decreased binding of the 110-kDa protein to the 5' UTR as visualized by EMSA. Absence of insulin increased binding of this trans-acting factor to the 5' UTR by 2-fold. Analysis of the 3' UTR showed no significant insulin-mediated changes in binding of trans-acting factors. We thus propose the existence of a novel RNA-binding insulin-sensitive factor that binds to the 5' UTR and may regulate apoB mRNA translation. Perturbations in hepatic insulin signaling as observed in insulin-resistant states may alter cis-trans interactions at the 5' UTR, leading to alterations in the rate of apoB mRNA translation, thus contributing to apoB-lipoprotein overproduction. 相似文献
90.
Light, the circadian clock, and sugar perception in the control of lignin biosynthesis 总被引:10,自引:0,他引:10
Rogers LA Dubos C Cullis IF Surman C Poole M Willment J Mansfield SD Campbell MM 《Journal of experimental botany》2005,56(416):1651-1663