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- Gadjieva, Rena, et al.
(författare)
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Analysis of gun phenotype in barley magnesium chelatase and Mg-protoporphyrin IX monomethyl ester cyclase mutants
- 2005
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Ingår i: Plant Physiology and Biochemistry. - : Elsevier BV. - 1873-2690 .- 0981-9428. ; 43:10-11, s. 901-908
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Tidskriftsartikel (refereegranskat)abstract
- The ability of barley (Hordeum vulgare L.) chlorophyll biosynthetic mutants to regulate the expression of Lhc genes was analyzed by a microarray approach. The Lhc genes are located in the nucleus and encode chlorophyll a/b binding proteins of the light-harvesting complex. The chlorophyll a/b binding proteins are some of the many proteins, which are imported to the chloroplast. It has been suggested that the chloroplast can regulate expression of nuclear genes encoding chloroplast proteins, using a chlorophyll biosynthetic intermediate such as Mg-protoporphyrin IX (MP) or Mg-protoporphyrin IX monomethyl ester (MPE) as a signal molecule. These compounds are intermediates between the two enzymes magnesium-chelatase (EC 6.6.1.1) and Mg-protoporphyrin IX monomethyl ester cyclase (EC 1.14.13.81) in the chlorophyll biosynthetic pathway. Genomes uncoupled (gun) mutants are defective in the chloroplast-to-nucleus signal transduction and express Lhc even when chloroplast development is inhibited by the herbicide norflurazon. We show that barley xantha-f, -g and -h mutants, defective in the three Mg-chelatase genes, have a gun phenotype. In contrast, a xantha-l mutant, defective in a gene of Mg-protoporphyrin monomethyl ester cyclase did not. Genome uncoupling in the xantha-f, -g, -h and -l mutants was also analyzed in absence of norflurazon. All mutants showed transcription of Lhc. This was unexpected in the case of xantha-l as this mutant showed accumulation of MPE, which has been suggested to be one of the two negative regulators of Lhc transcription. We suggest that chlorophyll intermediates may only function as signal molecules at an early developmental stage of chloroplast development.
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| 4. |
- Gadjieva, Rena, et al.
(författare)
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Fractionation of the thylakoid membranes from tobacco. A tentative isolation of ‘end membrane’ and purified ‘stroma lamellae’ membranes
- 1999
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Ingår i: Biochimica et Biophysica Acta - Bioenergetics. - 0005-2728. ; 1411:1, s. 92-100
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Tidskriftsartikel (refereegranskat)abstract
- Thylakoids isolated from tobacco were fragmented by sonication and the vesicles so obtained were separated by partitioning in aqueous polymer two-phase systems. By this procedure, grana vesicles were separated from stroma exposed membrane vesicles. The latter vesicles could be further fractionated by countercurrent distribution, with dextran-polyethylene glycol phase systems, and divided into two main populations, tentatively named 'stroma lamellae' and 'end membrane'. Both these vesicle preparations have high chlorophyll a/b ratio, high photosystem (PS) I and low PS II content, suggesting their origin from stroma exposed regions of the thylakoid. The two vesicle populations have been compared with respect to biochemical composition and photosynthetic activity. The 'end membrane' has a higher chlorophyll a/b ratio (5.7 vs. 4.7), higher P700 content (4.7 vs. 3.3 mmol/mol of chlorophyll). The 'end membrane' has the lowest PS II content, the ratio PS I/PS II being more than 10, as shown by EPR measurements. The PS II in both fractions is of the β-type. The decay of fluorescence is different for the two populations, the 'stroma lamellae' showing a very slow decay even in the presence of K3Fe(CN)6 as an acceptor. The two vesicle populations have very different surface properties: the end membranes prefer the upper phase much more than the stroma lamellae, a fact which was utilized for their separation. Arguments are presented which support the suggestion that the two vesicle populations originate from the grana end membranes and the stroma lamellae, respectively.
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| 6. |
- Gadjieva, Rena
(författare)
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Hebeloma species associated with Cistus
- 2009
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Ingår i: Mycological Research. - : Elsevier BV. - 0953-7562 .- 1469-8102. ; 113, s. 153-162
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Tidskriftsartikel (refereegranskat)abstract
- The genus Hebeloma has a number of species highly specific to Cistus and others that occur with several host genera. This paper discusses the species of Hebeloma that appear to be ectomycorrhizal with Cistus, judging from their occurrence when Cistus is the only available host. The previously unknown species H. plesiocistum Spec. nov. is described. We also provide a key to the known Hebeloma associates of Cistus. Molecular analyses based on ITS sequence data further illustrate the distinctness of the newly described species and difficulties in the species delimitation with view to H. erumpens. Specific associations with Cistus may have evolved more than once within the genus Hebeloma. (C) 2008 The British Mycological Society. Published by Elsevier Ltd. All rights reserved.
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| 8. |
- Gadjieva, Rena, et al.
(författare)
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Interconversion of Low- and High-Potential Forms of Cytochrome b559 in Tris-Washed Photosystem II Membranes under Aerobic and Anaerobic Conditions
- 1999
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Ingår i: Biochemistry. - : American Chemical Society (ACS). - 0006-2960 .- 1520-4995. ; 38:32, s. 10578-10584
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Tidskriftsartikel (refereegranskat)abstract
- In this study, the reversible conversion between the high- (HP) and low-potential (LP) forms of Cytb559 has been analyzed in Tris-washed photosystem II (PSII) enriched membranes. These samples are deprived of the Mn cluster of the water-oxidizing complex (WOC) and the extrinsic regulatory proteins. The results obtained by application of optical and EPR spectroscopy reveal that (i) under aerobic conditions, the vast majority of Cytb559 exhibits a low midpoint potential, (ii) after removal of O2 in the dark, a fraction of Cytb559 is converted to the high-potential form which reaches level of about 25% of the total Cytb559, (iii) a similar dark transformation of LP HP Cytb559 occurs under reducing conditions (8 mM hydroquinone), (iv) under anaerobic conditions and in the presence of 8 mM hydroquinone, about 60% of the Cytb559 attains the HP form, (v) the interconversion is reversible with the re-establishment of aerobic conditions, and (vi) aerobic and oxidizing conditions (2 mM ferricyanide or 0.5 mM potassium iridate) induce a decrease of the amount of the HP form, also showing that the conversion is reversible. This reversible interconversion between LP and HP Cytb559 is not observed in PSII membrane fragments with an intact WOC. On the basis of these findings, the possibility is discussed that the O2-dependent conversion of Cytb559 in PSII complexes lacking a functionally competent WOC is related to a protective role of Cytb559 in photoinhibition and/or that it is involved in the regulation of the assembly of a competent water-oxidizing complex in PSII.
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| 9. |
- Gadjieva, Rena, et al.
(författare)
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Nonsense-mediated mRNA decay in barley mutants allows the cloning of mutated genes by a microarray approach.
- 2004
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Ingår i: Plant Physiology and Biochemistry. - : Elsevier BV. - 1873-2690 .- 0981-9428. ; 42:7-8, s. 681-685
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Tidskriftsartikel (refereegranskat)abstract
- We have previously described a microarray approach to identify and clone genes from mutants of higher organisms. In the method cDNA of two mutants with similar phenotype are competitively hybridized to DNA clones arrayed on a glass slide. Clones corresponding to an mRNA that is not expressed in one of the strains due to a mutation will be specifically highlighted in the hybridization, which provides a possibility to identify and eventually clone the mutated gene. The approach is dependent on mutations that affect the amount of mRNA. Nonsense mutations, which prematurely terminate translation, can be such mutations as a surveillance system known as nonsense-mediated decay (NMD) has been developed by organisms to reduce the abundance of mRNA with nonsense codons. In the present study, we have analysed the barley (Hordeum vulgare L.) magnesium chelatase mutants xantha-f 26, xantha-f 27 and xantha-f 40 in order to investigate the presence of NMD in barley, as well as the importance of the position of the stop codon for NMD. Both nonsense-mutants xantha-f 27 and xantha-f 40, but not the missense mutant xantha-f 26, showed NMD. This was not expected for xantha-f 27 as its mutation is in the last exon of the gene. We conclude the NMD expands the number of mutants that can be used for gene cloning by our described microarray approach.
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