Mitochondria plant

Plant mitochondria are the main source of energy generation in photosynthetic cells in the dark and in nonphotosynthetic cells under all conditions. 

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

Ravanel, P. and M. Tissut. 1986. Toxicity of pentachlorophenol on isolated plant mitochondria. Phytochemistry. 25 577-583. 

OLIVER, D.J., The glycine decarboxylase complex from plant mitochondria, Anna. Rev. Plant Physiol. Plant Mol. Biol., 1994,45, 323-337. 

Moore AL, Beechey RB. Plant Mitochondria Structural, Functional and Physiological Aspects, Plenum Press, New York, 1987. 

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

Brennicke A, Kuck A. Plant Mitochondria with Emphasis on RNA. Editing and Cytoplasmic Male Sterility, VCH, Weinheim, Germany, 1993. 

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. 

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). 

In studies with Isolated plant mitochondria, flavones, flava-nones, cinnamic acids, and benzoic acids were shown to Inhibit the oxidation of succinate, malate, and NADH Inhibition was... 

Plant Mitochondria Have Alternative Mechanisms for Oxidizing NADH... 

Plant mitochondria supply the cell with ATP during periods of low illumination or darkness by mechanisms entirely analogous to those used by nonphotosynthetic organisms. In the light, the principal source of mitochondrial NADH is a reaction in which glycine, produced by a process known as photorespiration, is converted to serine (see Fig. 20-21) ... 

For reasons discussed in Chapter 20, plants must carry out this reaction even when they do not need NADH for ATP production. To regenerate NAD+ from unneeded NADH, plant mitochondria transfer electrons from NADH directly to ubiquinone and from ubiquinone directly to 02, bypassing Complexes III and IV and their proton pumps. In this process the energy in NADH is dissipated as heat, which can sometimes be of value to the plant (Box 19-1). Unlike cytochrome oxidase (Complex IV), the alternative QH2 oxidase is not inhibited by cyanide. Cyanide-resistant NADH oxidation is therefore the hallmark of this unique plant electron-transfer pathway. 

FIGURE 2 Electron carriers of the inner membrane of plant mitochondria. Electrons can flow through Complexes I, III, and IV, as in animal mitochondria, or through plant-specific alternative carriers by the paths shown with blue arrows. 

In addition to these major processes, many other chemical events also occur. Mitochondria concentrate Ca2+ ions and control the entrance and exit of Na+, K+, dicarboxylates, amino acids, ADP, P and ATP, and many other substances.16 Thus, they exert regulatory functions both on catabolic and biosynthetic sequences. The glycine decarboxylase system (Fig. 15-20) is found in the mitochondrial matrix and is especially active in plant mitochondria (Fig. 23-37). Several cytochrome P450-dependent hydroxylation reactions, important to the biosynthesis and catabolism of steroid hormones and... 

Mitochondrial electron transport in plants and fungi. Plant mitochondria resemble those of mammals in many ways, but they contain additional dehydrogenases and sometimes utilize alternative pathways of electron transport,68-73 as do fungi.74 Mitochondria are impermeable to NADH and NAD+. Animal mitochondria have shuttle systems (see Fig. 18-16) for bringing the reducing equivalents of NADH into mitochondria... 

A poly(A) "tail" consisting of -250 residues of adenylic acid is added next by poly(A) polymerase, a component of an enzyme complex that also cleaves the RNA chains.545 57111 Most eukaryotic mRNA is polyadenylated with the exception of that encoding histones. The function of the poly(A) is unclear. It is needed for transport of mRNA out of the nucleus, but it does confer a greatly increased stability to the mRNA in the cytoplasm where the adenylate irnits are gradually removed.307 308 In contrast, in chloroplasts and plant mitochondria polyadenylation is required for rapid degradation of mRNA.571c d Polyadenylation may also increase the efficiency of translation.572 Polyadenylation occurs rapidly within -1 min after transcription is completed. 

AL Moore, CK Wood, FZ Watts. Protein import into plant mitochondria. Annu Rev Plant Physiol Plant Mol Biol 45 545-575, 1994. 

Rugolo, M., Pistocchi, R., and Zannoni, D., Calcium ion transport in higher plant mitochondria (Helianthus tuberosus), Physiol. Plant., 79, 297-302, 1990. 

The thermogenic mechanism best understood in plants is a cyanide-insensitive nonpho-sphorylating electron transport pathway that is found only in plant mitochondria (Raskin et al., 1987). This pathway is distinct from the electron transport pathway involved in mitochondrial ATP production, and is under the control of calorigens, molecules that can lead to a... 

Mitochondria contain ubiquinone (also known as coenzyme Q), which differs from plastoquinone A (Chapter 5, Section 5.5B) by two methoxy groups in place of the methyl groups on the ring, and 10 instead of 9 isoprene units in the side chain. A c-type cytochrome, referred to as Cyt Ci in animal mitochondria, intervenes just before Cyt c a h-type cytochrome occurring in plant mitochondria is involved with an electron transfer that bypasses cytochrome oxidase on the way to 02. The cytochrome oxidase complex contains two Cyt a plus two Cyt a3 molecules and copper on an equimolar basis with the hemes (see Fig. 5-16). Both the Fe of the heme of Cyt a3 and the Cu are involved with the reduction of O2 to H20. Cytochromes a, >, and c are in approximately equal amounts in mitochondria (the ratios vary somewhat with plant species) flavoproteins are about 4 times, ubiquinones 7 to 10 times, and pyridine nucleotides 10 to 30 times more abundant than are individual cytochromes. Likewise, in chloro-plasts the quinones and the pyridine nucleotides are much more abundant than are the cytochromes (see Table 5-3). 

Logan, D.C. (Ed.) 2007. Plant Mitochondria, Annual Plant Reviews, Vol. 31 Blackwell, Oxford, UK. 

Krab, K., Wagner, M.J., Wagner, A.M. andMoller, I.M. (2000) Identification of the site where the electron transfer chain of plant mitochondria is stimulated by electrostatic charge screening. Eur. J. Biochem. 267, 869-876. 

To date, twelve transporters with different substrate specificities have been demonstrated in mammalian mitochondrial membranes - (cf.. Table 8.1). Plant mitochondria have a slightly different set [11]. Early studies of metabolite transport in mitochondria dating from the middle 1960s were concerned with identifying these transporters. More recently, research has been directed toward elucidation of molec-... 

---