Stress response cellular mechanisms

Morphological plasticity and cellular acclimation When plants are exposed to stress as a consequence of resource depletion or climatic fluctuation, many different responses are possible depending upon the species and the nature and severity of the stress. However, as Bradshaw (1965) recognised, stress responses can be classified into two basic types, one of which is morphological and the other physiological. One of the major uses of plant strategy theory is to provide a basis for predicting which of the two mechanisms is likely to be operative in particular species, populations and situations. 

Epithelial cells of the GI tract are exposed to various agents (as indicated in previous sections) and conditions that activate stress-response pathways. This results in either cell survival or cell death. Those cells with inadequate cellular defenses may die by one of three major cell death mechanisms, apoptosis, autophagy or necrosis, depending upon the particular stress conditions. 

Shyy, J.Y. and Chien, S. (1997) Role of integrins in cellular responses to mechanical stress and adhesion. Current Opinion in Cell Biology 9 707-713... 

Stamenovic D, Wang N. Cellular responses to mechanical stress, invited review Engineering approaches to cytoskeletal mechanics. J Appl Physiol. 2000 89 2085-2090. 

HDL HDL promote the cholesterol efflux from arterial. In addition, HDL protect LDL from oxidation and induction of subsequent cytotoxicity (Von Eckardstein et al., 2001 Kwiterovich, 1998 Berliner and Heinecke, 1996). This effect is apparently due to the presence of 2 enzymes (paraoxonase and PAF-acetylhydrolase bound to HDL) which may hydrolyse the oxidized lipids of LDL, thus blocking the subsequent biological responses (Hajjar and Haberland, 1997). Moreover, HDL could reduce hydroperoxides to their corresponding hydroxides, or extract oxidized lipids from oxidized LDL (Bonnefont-Rousselot et al., 1999). HDL inhibit oxidized LDL cytotoxicity (Hessler et al., 1979), through inhibition of oxT, DT. -induced stress and calcium rise. HDL act as an anti-oxidant lowering the oxidative modification of LDL, and preventing the cells of arterial wall from the deleterious effect of oxidized LDL, but their precise cellular mechanism of protection still remains unknown. 

There is not yet a clear understanding of the actual effectiveness of the use of classical preservatives such as organic acids in conjunction with other common components of food preservation systems. This entails the physiological and molecular mechanisms within cells and whether microorganisms die or adapt and survive as a result of this preservation. For example, which signal transduction systems are involved and which stress proteins are induced, how are these systems induced, and how much cellular energy (ATP) is involved in each system The amount of available energy will determine to what extent a microbial cell will activate the various stress response pathways (Brul and Coote, 1999). 

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