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Chloroplast Envelope (chloroplast + envelope)
Selected AbstractsPLASTID FATTY ACID BIOSYNTHESIS IN THE DIATOMS NITZSCHIA ALBA AND NITZSCHIA LAEVISJOURNAL OF PHYCOLOGY, Issue 2000K.M. McGinnis The role of the plastid in fatty acid biosynthesis in the non-photosynthetic diatom Nitzschia alba was studied and compared to that in the photosynthetic, closely related Nitzschia laevis. Transmission electron microscopy was used to analyze structural features of the plastid that may be relevant to biochemical function. Typical of a photosynthetic diatom, N. laevis had a chloroplast envelope composed of four membranes, and had abundant chloroplast ribosomes. The leucoplast of N. alba also had a multi-membrane envelope, chloroplast ribosomes, and a genome that encodes plastid specific proteins. This suggested that the plastid of N. alba may still possess the biochemical functions of the chloroplast, aside from photosynthesis. To determine whether plastidial fatty acid biosynthesis occurred in N. alba, the response of the two diatoms to the compound thiolactomycin was compared. Thiolactomycin has been shown to effect keto-acyl-ACP-synthases, and specifically inhibits the plastidial fatty acid biosynthetic pathway. While growth of N. alba was not impacted by thiolactomycin as in N. laevis, neutral lipid accumulation and fatty acid composition was impacted by thiolactomycin in both organisms. These findings suggest that the plastidial fatty acid biosynthetic pathway does exist in the leucoplast of N. alba, although it lacks photosynthetic capacity. [source] Re-examination of ultrastructures of the stellate chloroplast organization in brown algae: Structure and development of pyrenoidsPHYCOLOGICAL RESEARCH, Issue 3 2007Atsuko Tanaka SUMMARY Some taxa of brown algae have a so-called ,stellate' chloroplast arrangement composed of multiple chloroplasts arranged in a stellate configuration, or else a single chloroplast with radiating lobes. The fine structures of chloroplasts and pyrenoids have been studied, but the details of their membrane configurations as well as pyrenoid ontogeny have not been well understood. The ultrastructure of the single stellate chloroplast in Splachnidium rugosum and Scytothamnus australis were re-examined in the present study, as well as the stellate arrangement of chloroplasts in Asteronema ferruginea and Asterocladon interjectum, using freeze-substitution fixation. It was confirmed that the chloroplast envelope invaginated into the pyrenoid in Splachnidium rugosum, Scytothamnus australis and Asteronema ferruginea, but chloroplast endoplasmic reticulum (CER) remained on the surface of the chloroplast. The space between the invaginated chloroplast envelope and CER was filled with electron-dense material. In Asteronema ferruginea, CER surrounding each pyrenoid was closely appressed to the neighboring CER over the pyrenoids, so that the chloroplasts formed a stellate configuration; however, in the apical cells chloroplasts formed two or more loose groups, or were completely dispersed. The pyrenoids of Asterocladon interjectum did not have any invagination of the chloroplast envelope, but a unique membranous sac surrounded the pyrenoid complex and occasionally other organelles (e.g. mitochondria). Immunolocalization of ,-1,3-glucans showed that the membranous sac in Asterocladon interjectum did not contain photosynthetic products such as chrysolaminaran. Observations in the dividing cells of Splachnidium rugosum and Scytothamnus australis indicated that the pyrenoid in the center of the chloroplast enlarged and divided into two before or during chloroplast division. [source] pEffects of UV radiation on the ultrastructure of several red algaePHYCOLOGICAL RESEARCH, Issue 1 2003Frank Poppe SUMMARY The effect of ultraviolet (UV) radiation on the ultrastructure of four red algae, the endemic Antarctic Palmaria decipiens (Reinsch) Ricker and Phycodrys austrogeorgica Skottsberg, the Arctic-cold temperate Palmaria palmata (Linnaeus) O. Kuntze and the cosmopolitan Bangia atropurpurea (Roth) C. Agardh was studied. All four species showed a formation of ,inside-out' vesicles from the chloroplast thylakoids upon exposure to artificial UV-radiation. In P. decipiens, most vesicles were developed after 8 h and in P. palmata, after 48 h of UV exposure. In B. atropurpurea, vesi-culation of thylakoids was observed after 72 h of UV irradiation. In Ph. austrogeorgica, the chloroplast envelope and thylakoid membranes were damaged and the phycobilisomes became detached from the thylakoids after 12 h of UV exposure. Ultraviolet-induced changes in the membrane structure of mitochondria were observed in P. decipiens and P. palmata. However, in P. decipiens they were reversible as was the damage in chloroplast fine structure after 12 h of UV treatment. Protein crystals in Ph. austrogeorgica showed degradation after exposure to UV radiation. Different methods of fixation and embedding macroalgal material are discussed. These findings give insight into the fine structural changes which occur during and after UV exposure and indicate a relationship between the species dependent sensitivity to UV-exposure and the depth distribution of the different species. [source] The ultrastructure of chilling stressPLANT CELL & ENVIRONMENT, Issue 4 2000H. A. Kratsch ABSTRACT Chilling injury to crop plants was first described 70 years ago and has been systematically investigated with electron microscopy since the late 1960s. Chloroplasts are the first and most severely impacted organelle. Thylakoids swell and distort, starch granules disappear, and a peripheral reticulum (vesicles arising from inner membrane of chloroplast envelope) appears. Chloroplast disintegration follows prolonged chilling. Mitochondria, nuclei and other organelles are less susceptible to chilling injury. Organellar development and ontogeny may also be disrupted. The inherent chilling sensitivity of a plant, as well as the ability of some species to acclimate to chilling, influence the timing and appearance of ultrastructural injury with the resulting outcome being mild, moderate, or severe. Other environmental factors that exacerbate injury are irradiance, chilling duration, and water status. The physiological basis for chloroplast swelling may be linked to chilling-stable starch-degrading enzymes that produce soluble sugars thus lowering stromal water potential at a time when chloroplast photosynthate export is reduced. Thylakoid dilation appears to be related to photo-oxidative conditions produced during chilling in the light. The peripheral reticulum is proposed to increase surface area of the transport-limiting membrane (chloroplast inner membrane) in response to the chilling-induced reduction in metabolite transport. Many of the ultrastructural symptoms appearing during moderate stress resemble those seen in programmed cell death. Future research directions are discussed. [source] Protein- and energy-mediated targeting of chloroplast outer envelope membrane proteinsTHE PLANT JOURNAL, Issue 6 2005Nancy R. Hofmann Summary While the import of nuclear-encoded chloroplast proteins is relatively well studied, the targeting of proteins to the outer membrane of the chloroplast envelope is not. The insertion of most outer membrane proteins (OMP) is generally considered to occur without the utilization of energy or proteinaceous components. Recently, however, proteins have been shown to be involved in the integration of outer envelope protein 14 (OEP14), whose outer membrane insertion was previously thought to be spontaneous. Here we investigate the insertion of two proteins from Physcomitrella patens, PpOEP64-1 and PpOEP64-2 (formerly known as PpToc64-1 and PpToc64-2), into the outer membrane of chloroplasts. The association of PpOEP64-1 with chloroplasts was not affected by chloroplast pre-treatments. Its insertion into the membrane was affected, however, demonstrating the importance of measuring insertion specifically in these types of assays. We found that the insertion of PpOEP64-1, PpOEP64-2 and two other OMPs, OEP14 and digalactosyldiacylglycerol synthase 1 (DGD1), was reduced by either nucleotide depletion or proteolysis of the chloroplasts. Integration was also inhibited in the presence of an excess of an imported precursor protein. In addition, OEP14 competed with the insertion of the OEP64s and DGD1. These data demonstrate that the targeting of several OMPs involves proteins present in chloroplasts and requires nucleotides. Together with previous reports, our data suggest that OMPs in general do not insert spontaneously. [source] | ||||||||||||||||||||||