Endoplasmic reticulum plant cell

Shockey, J.M., S.K. Gidda, D.C. Chapital, et al. 2006. Tung tree DGATl and DGAT2 have nonredundant functions in triacylglycerol biosynthesis and are localized to different subdomains of the endoplasmic reticulum. Plant Cell 18 2294—2313. 

There are, however, many enzymes which, because they do not seem to be contained in such cellular particles, are referred to as soluble enzymes . Thus, the chemical reactions whereby the yeast cell converts glucose into ethanol and which seem to be identical with the first sequence of reactions in the normal respiration of plant cells are catalysed by such soluble enzymes. In the living cell such enzymes may, however, function as an organised multi-enzyme system which forms part of the endoplasmic reticulum. The fact that they cannot be obtained in association may merely reflect our inability to preserve the endoplasmic reticulum in cell-free preparations. Thus, in alcoholic fermentation by the yeast cell, which occurs in the absence of oxygen, there is an oxidative reaction which is balanced by a reduction. These both involve dehydrogenase enzymes having the same co-enzyme, nicotinamide adenine dinucleotide. One of these reactions, that catalysed by alcohol dehydrogenase, has already been mentioned (p. 73, eqn. 6). The other reaction... 

The cytochromes are iron-containing hemoproteins in which the iron atom oscillates between Fe + and Fe + during oxidation and reduction. Except for cytochrome oxidase (previously described), they are classified as dehydrogenases. In the respiratory chain, they are involved as carriers of electrons from flavoproteins on the one hand to cytochrome oxidase on the other (Figure 12-4). Several identifiable cytochromes occur in the respiratory chain, ie, cytochromes b, Cp c, a, and (cytochrome oxidase). Cytochromes are also found in other locations, eg, the endoplasmic reticulum (cytochromes P450 and h, and in plant cells, bacteria, and yeasts. 

Biosynthesis of Unsaturated Fatty Acids. In the mammalian tissues, the forma-tion of monoene fatty acids is only possible. Oleic acid is derived from stearic acid, and palmitooleic acid, from palmitic acid. This synthesis is carried out in the endoplasmic reticulum of the liver cells via the monooxigenase oxidation chain. Any other unsaturated fatty acids are not produced in the human organism and must be supplied in vegetable food (plants are capable of generating polyene fatty acids). Polyene fatty acids are essential food factors for mammals. 

Several molecular strategies have been successful in increasing foreign protein production in cultured plant cells. These include using promoters for inducible expression [10, 12, 29], optimizing codon usage [30] and adding the KDEL sequence to ensure protein retention in the endoplasmic reticulum [31]. Application of different... 

Proteins produced in plant cells can remain within the cell or are secreted into the apoplast via the bulk transport (secretory) pathway. In whole plants, because levels of protein accumulated intracellularly, e. g. using the KDEL sequence to ensure retention in the endoplasmic reticulum, are often higher than when the product is secreted [58], foreign proteins are generally not directed for secretion. However, as protein purification from plant biomass is potentially much more difficult and expensive than protein recovery from culture medium, protein secretion is considered an advantage in tissue culture systems. For economic harvesting from the medium, the protein should be stable once secreted and should accumulate to high levels in the extracellular environment. 

The plasmodesmata may be aggregated in primary pit fields or in the pit membranes between pit pahs. The plasmodesmata appear as narrow canals (2 pm) lined by a plasma membrane and are traversed by a des-motubule, a tubule of endoplasmic reticulum. The plasmodemata are dynamic altering their dimensions and are functionally diverse. For example, whereas some transport endogenous plant transcription factors, others transport numerous proteins from companion cells to enucleated sieve elements. 

Hepler PK, Palevitz BA, Lancelle SA, McCauley MM, Lichtschleidl I. Cortical endoplasmic reticulum in plant. J Cell Sci 1990 96 355-373. 

Ukaji N, Kuwabara C, Takezawa D, Arakawa K, Yoshida S, Fujikawa S. Accumulation of small heat shock protein homologs in the endoplasmic reticulum of cortical parenchyma cells in mulberry in association with seasonal cold acclimation. Plant Physiol 1999 120 481-490. 

Craig S, Staehelin LA. High pressure freezing of intact plant tissues. Evaluation and characterization of novel features of the endoplasmic reticulum and associated membrane systems. Eur J Cell Biol 1988 46 81-93. 

The most important membranes in animal cells are the plasma membrane, the inner and outer nuclear membranes, the membranes of the endoplasmic reticulum (ER) and the Golgi apparatus, and the inner and outer mitochondrial membranes. Lysosomes, peroxisomes, and various vesicles are also separated from the cytoplasm by membranes. In plants, additional membranes are seen in the plastids and vacuoles. All membranes show polarity—e., there is a difference in the composition of the inner layer (facing toward the cytoplasm) and the outer layer (facing away from it). 

The cell organellae in woody plants are the nucleus, mitochondrion, rough-endoplasmic reticulum (r-ER), smooth endoplasmic reticulum (s-ER), Golgi-body, plastid, vacuole, microbody, etc. Their functions are very complicated, and some have definite roles in the biosynthesis of cell-wall components. Hence, changes in size of cell organellae are likely to occur, since cell-wall composition depends upon the stage of wall development. 

Pagny, S., Cabanes-Macheteau, M., Gilikin, J.W., Leborgne-Castel, N., Lerouge, R, Boston, R.S., Faye, L., and Gomord, V. (2000). Protein recycling from the Golgi apparatus to the endoplasmic reticulum in plants and its minor contribution to calreticulin retention. Plant Cell 12 739-755. 

Vitale, A. and Denecke, J. (1999). The endoplasmic reticulum gateway of the secretory pathway. Plant Cell 11 615-628. 

Topical eukaryotic cells (Fig. 1-7) are much larger than prokaryotic cells—commonly 5 to 100 pm in diameter, with cell volumes a thousand to a million times larger than those of bacteria. The distinguishing characteristics of eukaryotes are the nucleus and a variety of membrane-bounded organelles with specific functions mitochondria, endoplasmic reticulum, Golgi complexes, and lysosomes. Plant cells also contain vacuoles and chloroplasts (Fig. 1-7). Also present in the cytoplasm of many cells are granules or droplets containing stored nutrients such as starch and fat. 

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