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Abstract. The chloroplastic isoform of glutamine synthetase (GS-2, EC 6.3.1.2) from Nicotiana tabacum L. is phosphorylated at the serine residues. At least three of the six GS-2 subunits separated by two-dimensional polyacrylamide gel electrophoresis cross-reacted with an antibody raised against phosphoserine. This provoked the question as to whether 14-3-3 proteins might be present in the chloroplast...
Abstract. The chloroplast ATP-dependent Clp protease (EC 3.4.21.92) is composed of the proteolytic subunit ClpP and the regulatory ATPase, ClpC. Although both subunits are found in the stroma, the interaction between the two is dynamic. When immunoprecipitation with antibodies against ClpC was performed on stroma from dark-adapted pea (Pisum sativum L. cv. Alaska) chloroplasts, ClpC but not ClpP was...
Abstract. Plant tetrapyrrole metabolism is located in two different organelles and distributes end products into the whole cell. A complex regulatory network is involved to prevent metabolic imbalance and inefficient allocation of intermediates as well as to correlate the metabolic activities with organelle development. This review presents new findings about the control of tetrapyrrole biosynthesis...
Abstract. Aging has received considerable attention in biomedicine, but little is known about the regulatory mechanisms responsible for the aging not associated with senescence in plants. This study provides new insights into the relationship between oxidative stress and plant aging, and points out chloroplasts as one of the target organelles of age-associated oxidative stress in plants. We simultaneously...
Abstract. Quantification of the expression levels of nuclear genes encoding plastid proteins under different genetic or environmental conditions can contribute to the genetic dissection of plastid functions. To facilitate such measurements, a set of 1,827 Arabidopsis thaliana genes coding for plastid proteins was PCR-amplified from genomic DNA and spotted on nylon membranes to generate an array of...
Abstract. Using a mass-spectrometric disequilibrium technique, net uptake of HCO3 and CO2 during steady-state photosynthesis was studied in whole cells and chloroplasts from the green algae Tetraedron minimum and Chlamydomonas noctigama, grown in air enriched with 5% (v/v) CO2 (high-CO2 cells) or in air [0.035% (v/v) CO2; low-CO2 cells]. High- and low-CO2 cells of both species were able to take up...
Abstract. Membrane-spanning transport proteins are responsible for the selective passage of most mineral nutrients and metabolites across cellular and intracellular membranes. This review's focus is on summarising the current state of research covering the molecular regulation and biochemical mechanisms involved in the transport of phosphorus, an often growth-limiting nutrient, in vascular plants...
It is widely believed that ferrochelatase (protoheme ferrolyase, EC 4.99.1.1), which catalyzes the insertion of ferrous ion into protoporphyrinIX to form protoheme, exists in both plastids and mitochondria of higher plants. By in vitro import assay with isolated pea (Pisum sativum L.) organelles, it has been proposed that one of two isoforms of ferrochelatase (type1) is dual-targeted into both plastids...
Pulse-amplitude modulated microfluorometry and an extracellular pH microprobe were used to examine light-induced spatial heterogeneity of photosynthetic and H+-transporting activities in cells of Chara corallina Klein ex Willd. Subcellular domains featuring different PSII photochemical activities were found to conform to alternate alkaline and acid zones produced near the cell surface, with peaks...
Genomic, proteomic, phylogenetic and evolutionary aspects of a novel gene encoding a putative chloroplast-targeted sulfate permease of prokaryotic origin in the green alga Chlamydomonas reinhardtii are described. This nuclear-encoded sulfate permease gene (SulP) contains four introns, whereas all other known chloroplast sulfate permease genes lack introns and are encoded by the chloroplast genome...
Intracellular proteases, together with molecular chaperones, are components of the cellular protein quality control system. Although the identity of chloroplast proteases has been revealed in recent years, little is known about their regulation. As a first step towards identifying unknown functional or regulatory components of the chloroplast proteolytic machinery, a genetic screen was devised with...
Transitory starch is formed in chloroplasts during the day and broken down at night. We investigated carbon export from chloroplasts resulting from transitory-starch breakdown. Starch-filled chloroplasts from spinach (Spinacia oleracea L. cv. Nordic IV) were isolated 1h after the beginning of the dark period and incubated for 2.5h, followed by centrifugation through silicone oil. Exported products...
A protein from Arabidopsis thaliana (L.) Heynh. showing homology to animal proteins of the NaPi-1 family, involved in the transport of inorganic phosphate, chloride, glutamate and sialic acid, has been characterized. This protein, named ANTR2 (for anion transporters) was shown by chloroplast subfractionation to be localized to the plastid inner envelope in both A. thaliana and Spinacia oleracea (L...
Plants respond to growth under different environmental conditions by adjusting the composition of the photosynthetic apparatus. To investigate the consequences of the acclimation strategies adopted by Arabidopsis thaliana, we have assessed the functioning of the photosynthetic apparatus in plants with very different chloroplast compositions. Using chlorophyll fluorescence analysis, we have determined...
l-myo-Inositol 1-phosphate synthase (EC 5.5.1.4; MIPS) catalyzes conversion of glucose 6-phosphate to l-myo-inositol 1-phosphate, the first and the rate-limiting step in the production of inositol, and has been reported from evolutionarily diverse organisms. Two forms of the enzyme have been characterized from higher plants, viz. cytosolic and chloroplastic, and the presence of MIPS has been earlier...
Plastid DNA, like bacterial and mitochondrial DNA, is organized into proteinDNA complexes called nucleoids. Plastid nucleoids are believed to be associated with the inner envelope in developing plastids and the thylakoid membranes in mature chloroplasts, but the mechanism for this localization is unknown. MFP1 is a DNA-binding, coiled-coil protein associated with the thylakoid membranes of mature...
A transglutaminase (TGase; EC 2.3.2.13) activity, which shared many properties with the TGase activity of the Helianthus tuberosus chloroplast, was observed in the Zea mays L. chloroplast and in its fractions. This activity was found to be prevalent in thylakoids; bis-(glutamyl) spermidine and bis-(glutamyl) putrescine were the main polyamine conjugates formed. Light stimulated the endogenous thylakoid...
Plastids bear their own genome, organized into DNA–protein complexes (nucleoids). Recently, we identified a DNA-binding protease (CND41) in the chloroplast nucleoids of cultured tobacco (Nicotiana tabacum L.) cells. In this study, we examine the biochemical function of this novel DNA-binding protease, particularly in senescent leaves, because antisense tobacco with a reduced amount of CND41 showed...
Plastids are known to be able to synthesize their own iron–sulfur clusters, but the biochemical machinery responsible for this process is not known. In this study it is investigated whether CpNifS, the chloroplastic NifS-like cysteine desulfurase of Arabidopsis thaliana (L.) Heynh. is responsible for the release of sulfur from cysteine for the biogenesis of iron–sulfur (Fe–S) clusters in chloroplasts...
The degradation of chloroplast proteins is an important occurrence in the mobilization of nutrients from senescing leaves to reproductive organs during senescence. Recently, we proved that tobacco CND41 protease is involved in Rubisco degradation and the translocation of nitrogen during senescence. In this study, we show the post-translational regulation of CND41 protease. Using very specific antibodies...
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