Search results for "Chloroplast"

Effect of Phosphinothricin (Glufosinate) on Photosynthesis and Photorespiration

1990

Phosphinothricin (PPT) causes a rapid inhibition of photosynthesis under atmospheric conditions (400 ppm CO2, 21% O2). However, under conditions (1000 ppm CO2, 2% O2) under which photorespiration cannot occur, there is no or only a very low rate of photosynthesis inhibition by phosphinothricin. Under both conditions, a strong NH4 +-accumulation is apparent caused through the inhibition of glutamine synthetase by phosphinothricin. This indicates, that NH4 +-accumulation cannot be the primary cause for photosynthesis inhibition by phosphinothricin, but a process in connexion with photorespiration plays a central role. Through the lack of amino donors, the transamination of glyoxylate to glyci…

Permanent plastid — nuclear complexes (PNCs) in plant cells

2008

Conventional opinion assumes random distribution of plastids in the plant cell and light regulated movement realised with a help of stromules and actin microfilaments. In several organisms from protists to plants the joining of chloroplasts to the nucleus has been mentioned as a phenomenon [1–3]. However, little is known what plants and tissues and how frequently contain these structures? Whether appearance of PNC in cell depends on the state of differentiation? What is physiologic role of the PNC.

IM30 triggers membrane fusion in cyanobacteria and chloroplasts

2015

The thylakoid membrane of chloroplasts and cyanobacteria is a unique internal membrane system harbouring the complexes of the photosynthetic electron transfer chain. Despite their apparent importance, little is known about the biogenesis and maintenance of thylakoid membranes. Although membrane fusion events are essential for the formation of thylakoid membranes, proteins involved in membrane fusion have yet to be identified in photosynthetic cells or organelles. Here we show that IM30, a conserved chloroplast and cyanobacterial protein of approximately 30 kDa binds as an oligomeric ring in a well-defined geometry specifically to membranes containing anionic lipids. Triggered by Mg2+, membr…

Endogenous fluctuations of DNA topology in the chloroplast of Chlamydomonas reinhardtii.

1998

DNA supercoiling in the chloroplast of the unicellular green alga Chlamydomonas reinhardtii was found to change with a diurnal rhythm in cells growing in alternating 12-h dark-12-h light periods. Highest and lowest DNA superhelicities occurred at the beginning and towards the end of the 12-h light periods, respectively. The fluctuations in DNA supercoiling occurred concurrently and in the same direction in two separate parts of the chloroplast genome, one containing the genes psaB, rbcL, and atpA and the other containing the atpB gene. Fluctuations were not confined to transcribed DNA regions, indicating simultaneous changes in DNA conformation all over the chloroplast genome. Because the d…

The redox state regulates RNA degradation in the chloroplast of Chlamydomonas reinhardtii.

1999

Abstract A Chlamydomonas reinhardtii chloroplast transformant, designated MU7, carrying a chimeric (rbcL promoter: β-glucuronidase [GUS]:psaB 3′ end) gene whose transcripts have been found previously to be unstable in light (half-life of 20 min in light as opposed to a half-life of 5 h in the dark), was used to study the role of electron transport and of the redox state in the degradation of chloroplast transcripts in the light. Blocking photosynthetic electron transport with 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) prevented the light-dependent breakdown of the pool of GUS transcripts in MU7 cells. Diamide, an oxidizing agent, caused a measurable delay in the degradation of GUS trans…

Phylogenetic relationship of the green alga Nanochlorum eukaryotum deduced from its chloroplast rRNA sequences.

1995

The marine green coccoidal alga Nanochlorum eukaryotum (N.e.) is of small size with an average diameter of 1.5 microns. It is characterized by primitive-appearing biochemical and morphological properties, which are considerably different from those of other green algae. Thus, it has been proposed that N.e. may be an early developed algal form. To prove this hypothesis, DNA of N.e. was isolated by a phenol extraction procedure, and the chloroplast DNA separated by preparative CsCl density-gradient centrifugation. The kinetic complexity of the nuclear and of the chloroplast DNA was evaluated by reassociation kinetics to 3 x 10(7) bp and 9 x 10(4) bp, respectively. Several chloroplast genes, i…

Processing of RNAs of the Family Avsunviroidae in Chlamydomonas reinhardtii Chloroplasts

2007

ABSTRACT The family Avsunviroidae comprises four viroid species with the ability to form hammerhead ribozymes that mediate self-cleavage of the multimeric plus and minus strands resulting from replication in the chloroplast through a symmetric rolling-circle mechanism. Research on these RNAs is restricted by their host range, which is limited to the plants wherein they were initially identified and some closely related species. Here we report cleavage and ligation in transplastomic Chlamydomonas reinhardtii expressing plus- and minus-strand dimeric transcripts of representative members of the family Avsunviroidae . Despite the absence of viroid RNA-RNA transcription, the C. reinhardtii -bas…

2013

Vesicle transfer processes in eukaryotes depend on specific proteins, which mediate the selective packing of cargo molecules for subsequent release out of the cells after vesicle fusion to the plasma membrane. The protein Tvp38 is conserved in yeasts and higher eukaryotes and potentially involved in vesicle transfer processes at the Golgi membrane. Members of the so-called “SNARE-associated proteins of the Tvp38-family” have also been identified in prokaryotes and those belong to the DedA protein family. Tvp38/DedA proteins are also conserved in cyanobacteria and chloroplasts. While only a single member of this family appears to be present in chloroplasts, cyanobacterial genomes typically e…

Vipp1: a very important protein in plastids?!

2011

As a key feature in oxygenic photosynthesis, thylakoid membranes play an essential role in the physiology of plants, algae, and cyanobacteria. Despite their importance in the process of oxygenic photosynthesis, their biogenesis has remained a mystery to the present day. A decade ago, vesicle-inducing protein in plastids 1 (Vipp1) was described to be involved in thylakoid membrane formation in chloroplasts and cyanobacteria. Most follow-up studies clearly linked Vipp1 to membranes and Vipp1 interactions as well as the defects observed after Vipp1 depletion in chloroplasts and cyanobacteria indicate that Vipp1 directly binds to membranes, locally stabilizes bilayer structures, and thereby ret…

Measurements of manganese in thylakoids of Sinapis alba grown under high-light and low-light conditions.

1981

The manganese content of thylakoids and tissues was measured in leaves grown under high- and low-light conditions. Especially when grown in a nutrient medium enriched in manganese (20 μM), the thylakoids contained large amounts of manganese, which could be removed by EDTA washing without impairment of the Hill reaction. The unremovable content of manganese was almost the same in thylakoids from plants grown in nutrient media of normal (2 μM) and reduced (0.2 μM) manganese content. Up to this limit of manganese content, Hill activity did not seem to be impaired. 1.2 atoms Mn per 100 molecules chlorophyll were found in low-light thylakoids and 1.6 atoms Mn in high-light thylakoids. This is si…