Ethylene protein synthesis

The ethylene-insensitive plants also showed reduced defense protein synthesis and were susceptible to soil pathogens to which they were normally fully resistant. In connection with the third trophic level, Kahl et al. (2000) found that attack by Manduca caterpillars on wild tobacco plants causes an ethylene burst that suppressed induced nicotine production but stimulated volatile emissions. They argued that the plant chooses to employ an indirect defense (the attraction of natural enemies) rather than a direct defense to which the attacker could adapt (Kahl et al, 2000 Winz and Baldwin, 2001). This implies that the plant is capable of identifying its attacker. We discuss this possibility in more detail in the discussion of specificity. 

The mechanism of toxicity of ethylene glycol involves metabolism, but unlike previous examples, this does not involve metabolic activation to a reactive metabolite. Thus, ethylene glycol is metabolized by several oxidation steps eventually to yield oxalic acid (Fig. 7.84). The first step is catalyzed by the enzyme alcohol dehydrogenase, and herein lies the key to treatment of poisoning. The result of each of the metabolic steps is the production of NADH. The imbalance in the level of this in the body is adjusted by oxidation to NAD coupled to the production of lactate. There is thus an increase in the level of lactate, and lactic acidosis may result. Also, the intermediate metabolites of ethylene glycol have metabolic effects such as the inhibition of oxidative phosphorylation, glucose metabolism, Krebs cycle, protein synthesis, RNA synthesis, and DNA replication. 

Figure 4. Effect of inhibitors of RNA and protein synthesis on ethylene production in subhook sections of etiolated pea seedlings.

Fruit tissues respond to ethylene by exhibiting increases in the activities of enzymes that catalyze ripening reactions, and in some cases, the increases in enzyme activity probably are the result of de novo synthesis, rather than activation of preexisting enzymes. Other target tissues respond similarly to ethylene. But it is not known whether ethylene acts directly to evoke new enzyme production. Interpretation of results with inhibitors of RNA and protein synthesis is inconclusive, because it could be merely that RNA and protein synthesis are essential to maintain the cells in a state competent to respond to ethylene. Moreover, there are some responses to ethylene, besides fruit ripening, which occur under conditions which apparently do not directly involve RNA and protein synthesis (e.g., membrane permeability changes). It has been proposed that the in vivo ethylene receptor site contains a metal such as copper (34,35). 

Plants, in common with microorganisms and animals, require methionine chiefly for three roles, (a) As a component of protein, a role which accounts for most of the methionine in the cell, (b) As a component of methionyl tRNA (in eukaryotes) and formylmethionyl tRNA (in chloroplasts, mitochondria, and prokaryotes), factors required for initiation of protein synthesis. (c) As a component of AdoMet, the chief biological methyl donor, the obligatory precursor of spermidine and spermine, and an effector of certain enzymes. In addition to these chief roles, a major pathway for the metabolism of methionine in certain plant tissues is its conversion to ethylene (see Yang and Adams, this series, Vol. 4, Chapter 6). Only plants and microorganisms can synthesize the homocysteine moiety of methionine novo, and the importance of this synthesis in the sulfur cycle has been noted in the introduction. 

Thus, cell enlargement, for instance, depends upon auxin and involves the uptake of water, extension of the cell membrane and protein synthesis. The auxin dose-response curve consists of two peirts promotion by low concentrations and inhibition by higher concentrations via the formation of ethylene. Cytokinins and abscisic acid may possibly induce also, under special conditions, the production of ethylene. Many publications deal with effects of these plant hormones, especially of auxin, on ethylene biosynthesis in plants which occurs after a lag phase of 30 - 60 minutes and is specifically blocked by rhizobitoxin as well as by inhibitors of ENA and protein synthesis indicating that a continuous synthesis of protein is required for high rate of ethylene production (Eef. 20). 

Respiration and other metabolic reactions continue at least for a while after the harvesting of fruit and vegetables. During ripening, the fruit enters the climateric phase in which there is enhanced respiration with ATP, RNA and protein synthesis, the production of ethylene and in some cases changes in the content of sugar phosphates. 

The binders vary quite widely—the most common being starch, soy protein and latexes in conjunction with other soluble polymers. Styrene-butadiene latexes have been the most popular but ethylene-vinyl acetate binders are also used. The method of polymer synthesis provides a way of modifying the properties of the latex. For example, adjustment of the ratio of styrene butadiene in the co-polymer gives rise to different degrees of softness or hardness. This property has a profound influence on the quality of the coating. It is also possible to co-polymerise monomers so as to introduce, for example, carboxy groups on to the surface of the latex particle which in turn assist in... 

Graft copolymers of nylon, protein, cellulose, starch, copolymers, or vinyl alcohol have been prepared by the reaction of ethylene oxide with these polymers. Graft copolymers are also produced when styrene is polymerized by Lewis acids in the presence of poly-p-methoxystyrene. The Merrifield synthesis of polypeptides is also based on graft copolymers formed from chloromethaylated PS. Thus, the variety of graft copolymers is great. 

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