Membrane limited vacuole

Metals, which enter aquatic organisms directly from the surrounding water, are compartmentalized within tissues in membrane-limited vacuoles and bound to ligands to reduce the toxic reactivity (Roesijadi 1992, Viarengo and Nott 1993). Amiard (1988) suggested that phytoplankton fixes metals and makes them unavailable to oysters. Compartmentalization processes remove metals from tissue fluids, and diffusion gradients inwards from surrounding water are maintained (Nott 1998). 

Most plant cells contain at least one membrane-limited Internal vacuole. The number and size of vacuoles depend on both the type of cell and its stage of development a single vacuole may occupy as much as 80 percent of a mature plant cell (Figure 5-24). A variety of transport proteins in the vacuolar membrane allow plant cells to accumulate and store water, ions, and nutrients (e.g., sucrose, amino acids) within vacuoles (Chapter 7). Like a lysosome, the lumen of a vacuole contains a battery of degradatlve enzymes and has an acidic pH, which is maintained by similar transport proteins in the vacuolar membrane. Thus plant vacuoles may also have a degradatlve... 

The geometry of cell construction provides another important aspect of metabolic control. In a bacterium, the periplasmic space (Fig. 8-28) provides a compartment that is separate from the cytosol. Some enzymes are localized in this space and do not mix with those within the cell. Other enzymes are fixed within or attached to the membrane. Eukaryotic cells have more compartments nuclei, mitochondria (containing both matrix and intermembrane spaces), lysosomes, microbodies, plastids, and vacuoles. Within the cytosol the tubules and vesicles of the endoplasmic reticulum (ER) separate off other membrane-bounded compartments. The rate of transport of metabolites through the membranes between compartments is limited and often is controlled tightly. 

Reese C, Mayer A (2005) Transition from hemifusion to pore opening is rate limiting for vacuole membrane fusion. J Cell Biol 171 981-90... 

The vacuole, often the largest organelle, is limited by a single membrane, the tonoplast. There is controversy about what the vacuole does. Three functions are attributed to it, namely, (i) osmotic regulation (ii) storage of such compounds as amino acids, purines, sugars, and phosphate and (Hi) that of a lysosome, a compartment in which breakdown reactions of such macromolecules as proteins and nucleic acids are separated from active synthesis in the cytoplasm. The subject is reviewed in Refs. 93 and 122. 

Apoptosis is delayed and may be maximal at 24-48 h after an insult. However, apoptotic cells can be seen even within 6 h of an insult, but are not common. Apoptosis involves condensation of the nucleus. Condensation of the cytoplasm occurs with large vacuole formation. Some mitochondria may condense. Very uncommonly, some mitochondria swell in apoptosis. The cell splits up into membrane-bound apoptotic bodies that can be seen in the limit areas surrounding the core of an infarction. Apoptosis is a programmed form of cell death that occurs following a small but sufficient amount of damage to a cell. This initiates a program that eventually kills the cell. 

For labeling the plasma membrane, a series of styryl dyes with different spectral properties is available (17). FM4-64, FM2-10, and FMl S have been tested for the use with Dictyostelium. For the combination with GFP-tagged proteins, FM4-64 offers the advantage of being excitable at the same wavelength (488 or 491 nm), and easily separated from GFP by its emission peak above 700 nm (14). All these styryl dyes label first the plasma membrane and then redistribute within a few minutes to membranes of the contractile vacuole system and of endosomes. Therefore, they should be added to the cells immediately before imaging of the plasma membrane is attempted. Since cells tend to round up as the dyes are integrated into the lipid layer of the membrane, concentrations should be kept at the lowest limit. 

In rats kept in a hypobaric chamber at a pressure of 460 mm Hg, Laidler and Kay (1975) found a U-near relation between the combined total volume of the carotid bodies and the combined volume of glomic cells (r = 0.92, P <0.001). There was a Unear relation between the volume of glomic ceUs and the duration of exposure (27, 28, and 35 days, respectively) to chronic hypoxia (r = 0.63, P = 0.05). The type I cells were enlarged due to an increase in the volume of their cytoplasm (Laidler and Kay (1978). Many of their dense-core vesicles were vacuolated and the core was displaced eccentrically to become adherent to the limiting membrane of the vesicle. The concentration and distribution of dense core vesicles remained unaltered and there were no obvious changes in the mitochondria, ribosomes or Golgi apparatus. There were no structural changes in the type II cells. 

The final step in the biosynthesis of ethylene is catalyzed by ACC oxidase. Application of ACC to most plant tissues results in a marked increase in ethylene production, indicating that ACC oxidase in these tissues is constitutive and not rate-limiting. Although ACC-dependent ethylene production is readily demonstrated in intact tissues, in vitro ACC oxidase activity has not been demonstrated independent of intact cellular material. Although intact protoplasts and vacuoles retained the characteristics of tissue ACC oxidase activity [9], Porter and John [24] reported that their preparations retained less than 5% of the activity associated with the parent tissue. They proposed that full ACC oxidase activity requires tissue integrity in addition to the previously noted cell membrane integrity. 

Ethanol strongly limits amino acid transport. It modifies the composition and the properties of the phospholipids of the plasmic membrane. The membrane becomes more permeable. The H+ ions of the medium massively penetrate the interior of the cell by simple diffusion. The membrane ATPase must increase its operation to control the intracellular pH. As soon as this task monopolizes the ATPase, the symport of the amino acids no longer functions. In other words, at the beginning of fermentation, and for as long as the ethanol concentration in the must is low, yeasts can rapidly assimilate amino acids and concentrate them in the vacuoles for later use, according to then-biosynthesis needs. 

Activation of inactive proenzymes by limited proteolysis Small vacuoles release pro-teinases Outside vacuole (cell, membrane, etc.) Activation of chitin synthase Restriction of proteolysis to site of chitin synthase activation... 

Fig. 4. Pertusaria pertusa. (1) Ascospore wall illustrating various layers. x4000. (2) Outer region of ascospore wall, x 16000. (3) Layer with orientated microfibrils, x 22000. (4) Germ tube. X 6000. m, medulla v, vacuoles 1, limiting membrane n, nuclei. From Pyatt (1969b).

In higher plants, the lipolytic enzymes and their physiological functions are not well characterized [1]. iMost reports demonstrated that phospholipid catabolism in plants is achieved by the concerted actions of membrane-bound enzymes including phospholipase D, phosphatidate phosphatase, lipolytic acyl hydrolases and lipoxygenases [1,2]. With the exception of the phospholipase D, the literature on plant phospholipases is still very limited. We previously reported that tonoplast from Acer pseudoplatanus cells contains small amounts of phosphatidic acid and lysophospholipids, which were produced together with free fatty acids, particularly after addition of Ca " [31. These data suggested the possible involvement of phospholipase D and phospholipase A in the metabolism of vacuolar membrane lipids. The phospholipase activities were studied by following the hydrolysis of added sn-2-[14c]linoleyl-PC to tonoplast vesicles. Tonoplast was obtained by osmotic lysis of pure preparations of vacuoles isolated from protoplasts derived from Acer pseudoplatanus cells [4]. This present work demonstrated clearly the presence of phospholipase D and phospholipase Ai activities associated with the tonoplast of Acer, The phospholipase Ai showed an optimal activity at pH about 6-6.5, did not necessarily require divalent cations, but was stimulated by Mg- and particularly by Ca. This work presents the first evidence for the presence of phospholipases A in plant cells. 

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