Cell collapse

If a section cut through a small sulfur-burned area of a lemon injured on the tree is examined microscopically, coagulation of protoplasm and cell collapse are apparent. Also, the injured tissue stains abnormally dark with safranin indicating the protoplasm has become more acidic than in normal tissue (18). Sides of the peel of lemons burned by sulfur on the tree were found to be higher in total sulfate than were uninjured sides of the same peel. The high total sulfate content of the peel was subsequently found to be due in part to soluble sulfate, as shown by analyses of the expressed cell solution (18). 

During the process, the solute diffuses into the intercellular space and, depending on the characteristics of the solute, it may pass through the membrane and enter the intracellular space. Differences in chemical potentials of water and solutes in the system result in fluxes of several components of the material and solution water drain and solute uptake are the two main simultaneous flows. Together with the changes in chemical composition of the food material, structural changes such as shrinkage, porosity reduction, and cell collapse take place and influence mass transfer behavior in the tissue. 

The second step of the proposed chain of events, resistance as a direct consequence of cell death, is still controversial (82-86). In the wheat-stem rust system, evidence favouring the idea of hypersensitive cell death as the cause of resistance (30,31,87-90) contrasts to results suggesting cell collapse as being a mere consequence of a yet unknown preceding resistance mechanism (90-97). 

The 3-deoxyanthocyanidins are a class of phytoalexins found in sorghum. These compounds are so fungi-toxic that they are effective at femtogram levels (Snyder and Nicholson, 1990 Nicholson and Wood, 2001). The synthesis of these compounds is initiated on the endoplasmic reticulum. Compounds are then trafficked in subcellular inclusions. The inclusions appear similar to vesicles, but there is no evidence that membranes surround the inclusions (Snyder and Nicholson, 1990). Nielsen et al. (2004) recently summarized this defense response. The cytological response commences when clear, colorless inclusions (less than 0.1 pm in diameter) accumulate in leaf cells under fungal attack. The inclusions eventually are seen as red bodies at the infection site. When the 3-deoxyanthocyanidins enter the apoplast, the host cell collapses. The phytoalexins then accumulate in the pathogen and cause its death. Excess phytoalexins are trapped in host cell walls at infection sites (Lo et al., 1998 1999). 

The DISC-induced procaspase assembly results in the autoactivation of caspases 8 and 10. The DISC process of caspase activation seems to be analogous to the apoptosome process of caspase 9 activation. Caspase 8, in turn, cleaves and activates caspase 3, which is responsible for the apoptotic signal amplification with subsequent cell collapse. 

Cotton bolls dehisce at maturity, leaving the fibers fully exposed to air and sunlight. The water content of the fiber decreases rapidly, the cytoplasm dries against the inner surface of the wall, and a large lumen is left where the central vacuole was once located. The formerly tube-shaped cell collapses and assumes a twisted ribbon conformation with a kidney-like cross-sectional pattern. These twists, or convolutions, permit the spinning of fiber cells into yarns. 

The structure of a foam, which deforms in a specific manner also influences physical properties. Upon initial compression there is a deformation of the structure that requires an increase in the amount of force applied. Once the foam has been deformed significantly the sides of the cell walls buckle leading to cell collapse and the production of elliptically deformed structures. A picture of such cells deformed under extreme compression is shown in Figure 14. During this phase of the compression the rate of increase in the force applied is significantly decreased. 

When compression and/or shear rise sufficiently, the symmetrical elasticity of the unit cell collapses, and the cell walls begin to buckle (Figure 6.26). The response to increased stress no longer produces a linear strain, and the material begins to respond to nonlinear elastic behavior, characterized by region B in Figure 6.22. 

Under natural conditions of slow freezing, the cell collapse that accompanies extracellular freezing subjects the cells to another kind of physical stress, as pointed out 50 years ago by Iljin. Instead of expanding,... 

Figure I. Spirogyra (X300). (a) Normal, unfrozen, (b) frozen extracellularly showing cell collapse without any ice inside the cell, (c) thawed. From Molisch,...

These principles formed the basis for producing high quality carrots and potatoes by a process of biopolymer infusion followed by high temperature short time fluidized bed dehydration. Infused biopolymers was shown to penetrate intracellular spaces and cell walls and may contribute to reduced cell collapse in the dehydration process. Deposition of infused biopolymer within the cells was elucidated using a convalently bound complex of biopolymer and colored dye which was visible upon histochemical examinations under a microscope. The dehydration process was optimized with response surface methodology. The resulting products have excellent quality, high rehydration ratio and a puffed structure. 

The theoretical basis of the new process are described in previous paragraphs. Incorporation of natural biopolymers into the cell structure may strengthen the cell walls and/or fill the intracellular spaces to prevent total cell collapse in the dehydration process. Furthermore, rapid drying in a HTST fluidized bed dryer develops a porous structure which may enhance water penetration on rehydration. 

The dye-biopolymer complexes were seen at intracellular spaces in intact carrot cells (Fig. 3a) and adhered to cell walls in broken cells (Fig. 3b). These pictures provided some evidence for our hypothesis that the biopolymers migrate on and around cell walls and their presence may have assisted in preventing or reducing cell collapse during dehydration. Much work needs to be done to elucidate the role of biopolymers on quality improvement of dehydrated vegetable pieces, and to define the proper size of molecules that would accomplish the desired texture. 

Basic principles in physio-chemical changes occurring during dehydration provided an effective approach to improve quality of dehydrated products. Carrot and potato dices infused with biopolymers before dehydration and processed under optimal conditions had good texture, high rehydration properties, good color and puffed appearance. Infused biopolymers were deposited on cell walls and intracellular spaces and may contribute to prevent cell collapse. 

Fried foods shrink when the moisture is lost and the food cells collapse as a consequence of heating and evaporation during frying. It is a phenomenon described as... 

Direct waterlogged wood impregnation by aqueous emulsion of styrene, methyl acrylate, and methyl methacrylate. Of these methods, only styrene emulsion was stable. Ash samples were immersed in styrene emulsion, and in situ radiation curing was then performed at a dose rate of 6 kGy/h (0.6 Mrad/h) for 30 h. Treated samples presented severe shrinkage and cell collapse because of a very low extent of impregnation (i). Another water-monomer exchange obtained with the 2-hydroxyethyl methacrylate monomer did not give satisfactory results (2). 

At a later stage of injury palisade parenchyma cells collapsed adjacent to collapsed epidermal cells. The area of injured epidermis in most lesions increased in diameter so that ten to fifteen epidermal cells comprised the lesion when palisade cells... 

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