Mitochondria in plants

Olyslaegers G, Verbelin J-P. Improved staining of F-actin and co-localisation of mitochondria in plant cells. J Microsc 1998 192 73-77. 

The mitochondrial matrix is the major site of fatty acid oxidation in animal cells, but in certain cells other compartments also contain enzymes capable of oxidizing fatty acids to acetyl-CoA, by a pathway similar to, but not identical with, that in mitochondria In plant cells, the major site of /3 oxidation is not mitochondria but peroxisomes. 

The inefficiency of rubisco determines that some carbon dioxide must remain in the air, and, conversely, that all the oxygen is not consumed. Overall, in modem organisms, the subtly switched cybernetic balance between the power-generation needs of the mitochondria in plants and animals, burning reduced carbon in oxygen to provide energy, and the photosynthetic restorative capacity of the chloroplasts, may set the daily account of planetary inputs and outputs of carbon dioxide and oxygen (Joshi Tabita 1996). 

C. Type 6 Cytochromes in Plant Mitochondria In plant mitochondria, as in mammalian mitochondria, there are probably three kinds of type 6 cytochromes 22,262-265). They are called cytochromes 6-565, 6-560, and 6-556 from the a peak of the reduced minus oxidized spectra at room temperature or, sometimes, 6502, 6557, and 6553, respectively, from those at the liquid nitrogen temperature. The Eo of cytochromes 6-565, 6-560, and 6-556 are —77 mV, - -42 mV, and —75 mV, respectively 266). An oxygen pulse experiment 267) has shown that cytochrome 6-560 is most rapidly oxidzed, with a half-time... 

The measurement of ATP-synthesis rate is also very helpful to investigate phosphorylation processes in chromatophores, energy synthesis by mitochondria in plant and animal cells and metabolic changes in microorganisms. This method can give detailed information about cell membrane damage in cytolysis of erythrocytes and thrombocytes, which is an important factor in blood preservation and extraction of active blood products. BL estimation of ATP is well established in cell culture for tissue and organ transplants. 

In animal, yeast, and fungal cells, DNA is present in two organelles, the nucleus and the mitochondria. In plant and algal cells, DNA is present in plastids (of which chloroplasts are one example) as well as in mitochondria and the nucleus. Unlike the DNA in the nucleus, which is packaged into chromosomes, plastid DNA and mitochondrial DNA are circular and thus resemble the DNA in prokaryotes (e.g., bacteria). 

Pyruvate carboxylase is the most important of the anaplerotie reactions. It exists in the mitochondria of animal cells but not in plants, and it provides a direct link between glycolysis and the TCA cycle. The enzyme is tetrameric and contains covalently bound biotin and an Mg site on each subunit. (It is examined in greater detail in our discussion of gluconeogenesis in Chapter 23.) Pyruvate carboxylase has an absolute allosteric requirement for acetyl-CoA. Thus, when acetyl-CoA levels exceed the oxaloacetate supply, allosteric activation of pyruvate carboxylase by acetyl-CoA raises oxaloacetate levels, so that the excess acetyl-CoA can enter the TCA cycle. 

Beta oxidation doe.s not occnr. significantly in plant mitochondria. 

Pterins make no contributions to the colors of plants and microorganisms. One important pterin is the folate produced by plants and microorganisms. Folate and its derivatives are present in plants in various concentrations in mitochondria, cytosols, vacuoles, and plastids. The total amount of fohc acid depends on the plant species, on the developmental stage, and on external factors. Good sources of folates are beans, lentils, spinach, and wheat germ. ... 

The individual steps of the multistep chemical reduction of COj with the aid of NADPHj require an energy supply. This supply is secured by participation of ATP molecules in these steps. The chloroplasts of plants contain few mitochondria. Hence, the ATP molecules are formed in plants not by oxidative phosphorylation of ADP but by a phosphorylation reaction coupled with the individual steps of the photosynthesis reaction, particularly with the steps in the transition from PSII to PSI. The mechanism of ATP synthesis evidently is similar to the electrochemical mechanism involved in their formation by oxidative phosphorylation owing to concentration gradients of the hydrogen ions between the two sides of internal chloroplast membranes, a certain membrane potential develops on account of which the ATP can be synthesized from ADP. Three molecules of ATP are involved in the reaction per molecule of COj. 

Lohse, S., W. Schliemann et al. (2005). Organization and metabolism of plastids and mitochondria in arbuscu-lar mycorrhizal roots of Medicago truncatula. Plant Physiol. 139(1) 329-340. 

The eukaryotes these include animals, plants, fungi and protozoa, the DNA of which is enclosed in a membrane-enclosed organelle (the cell nucleus). They have a cytoskeleton (a fine membrane-like network in the interior of the cell, which provides stability) and contain mitochondria. Higher plants, as well as algae, are equipped with chloroplasts for photosynthesis. 

We shall see that the photosynthesis becomes isolated in plant chemotypes using derivatives of photosynthesising bacteria, chloroplasts, while degradation will be found in plants (no light), fungi and animals using derivatives of non-photosynthesising bacteria, mitochondria. These are cases of symbiosis. 

The development of eukaryotes has a major novel feature their largest energy sources are in two organelles. They all have mitochondria and plants have... 

Liu, Z. J., Bushnell, W. R. and Brambl, R. (1987). Potentiometric cyanine dyes are sensitive probes for mitochondria in intact plant-cells - Kinetin enhances mitochondrial fluorescence. Plant Physiol. 84, 1385-1390. 

Bacteria normally harbour a single, circular chromosome that tends to be tethered to the bacterial plasma membrane and tends to have few if any closely associated proteins. Many bacteria also contain extra-chromosomal DNA in the form of plasmids, as will be discussed later. Eukaryotes (plants, animals and yeasts) posses multiple linear chromosomes contained within a cell nucleus, and these chromosomes are normally closely associated with proteins termed histones (the pro-tein-DNA complex is termed chromatin). Eukaryotes also invariably possess DNA sequences within mitochondria and in chloroplasts in plants. The (usually circular) DNA molecules are much... 

Douce, R. Mitochondria in Higher Plants, American Society of Plant Physiologists monograph. Academic Press, New York, 1985. 

HisselR, WissingerB, Schuster W, Brennicke A. RNA editing in plant mitochondria. Science 1989 246 1632-1634. 

Binder S, Marchfelder A, Brennicke A. Regulation of gene expression in plant mitochondria. Plant Mol Biol 1996 32 303-314. 

Maier RM,ZeltzP, KosselH. BonnardG,Gualberto JM, Grienenberger JM. RNA editing in plant mitochondria and chloroplasts. Plant Mol Biol 1996 32 343-365. 

Whereas DNA is mostly located in the nucleus of cells in higher organisms (with some also in mitochondria and in plant chloroplasts), RNA comes in three major and distinct forms, each of which plays a crucial role in protein biosynthesis in the cytoplasm. These are, respectively, ribosomal RNA (rRNA), which represents two-thirds of the mass of the ribosome, messenger RNA (mRNA), which encodes the information for the sequence of proteins, and transfer RNAs (tRNAs) which serve as adaptor molecules, allowing the 4-letter code of nucleic acids to be translated into the 20-letter code of proteins. These latter molecules contain a substantial number of modified bases, which are introduced enzymatically. 

Electron-transfer chains in plants differ in several striking aspects from their mammalian counterparts. Plant mitochondria are well known to contain alternative oxidase that couples oxidation of hydroquinones (e.g., ubiquinol) directly to reduction of oxygen. Semiquinones (anion-radicals) and superoxide ions are formed in such reactions. The alternative oxidase thus provides a bypass to the conventional cytochrome electron-transfer pathway and allows plants to respire in the presence of compounds such as cyanides and carbon monoxide. There are a number of studies on this problem (e.g., see Affourtit et al. 2000, references therein). 

The oxidation of aciy lic acid can be rationalized in terms of the endogenous catabolism of propionic acid, in which acrylyl coenzyme A is an intermediate. This pathway is analogous with fatty acid 3-oxidation, common to all species and, unlike the corresponding pathway in plants, does not involve vitamin 8,2. 3-Hydroxypropionic acid has been found as an intennediate in the metabolism of acrylic acid in vitro in rat liver and mitochondria (Finch Frederick, 1992). The CO2 excreted derives from the carboxyl carbon, while carbon atoms 2 and 3 are converted to acetyl coenzyme A, which participates in a variety of reactions. The oxidation of acrylic acid is catalysed by enzymes in a variety of tissues (Black Finch, 1995). In mice, the greatest activity was found in kidney, which was five times more active than liver and 50 times more active than skin (Black et al., 1993). 

Membrane-bounded organelles Absent Mitochondria, chloroplasts (in plants, some algae), endoplasmic reticulum, Golgi complexes, lysosomes (in animals), etc. 

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