Secondary compound , production

There are many exceptions to these general observations. Small changes greatly affect the secondary compounds produced, if they occur early in the biosynthetic route. Further, it is easier to lose than to gain the ability to synthesize and accumulate a particular compound. Thus, it is not surprising to find many instances of apparent reversals in biosynthetic capacity. This should particularly be true in instances where the initial selection pressures that favored the presence of the compounds have disappeared. Species of plants that occur on islands (presumably with lower herbivore pressures) often have reduced secondary compound production and accumulation in comparison to mainland species of the same genus (Mabry, 1973 Seeligmann and Alston, 1967). 

Inhibition of Nitrosamine Formation. Nitrites can react with secondary amines and A/-substituted amides under the acidic conditions of the stomach to form /V-nitrosamines and A/-nitrosamides. These compounds are collectively called N-nitroso compounds. There is strong circumstantial evidence that in vivo A/-nitroso compounds production contributes to the etiology of cancer of the stomach (135,136), esophagus (136,137), and nasopharynx (136,138). Ascorbic acid consumption is negatively correlated with the incidence of these cancers, due to ascorbic acid inhibition of in vivo A/-nitroso compound formation (139). The concentration of A/-nitroso compounds formed in the stomach depends on the nitrate and nitrite intake. 

The photochemical cycloadditions of alkenes and alkynes with aromatic compounds have received by far the most attention. Yields of [2+2] cydoadducts can be good, but reaction times are often long and secondary rearrangement products are common [139, 140, 141,142, 143,144, 145,146] (equations 63-65). The pioneering mechanistic and synthetic work on aromatic photocycloadditions has been reviewed [147],... 

A number of methods are available for following the oxidative behaviour of food samples. The consumption of oxygen and the ESR detection of radicals, either directly or indirectly by spin trapping, can be used to follow the initial steps during oxidation (Andersen and Skibsted, 2002). The formation of primary oxidation products, such as hydroperoxides and conjugated dienes, and secondary oxidation products (carbohydrides, carbonyl compounds and acids) in the case of lipid oxidation, can be quantified by several standard chemical and physical analytical methods (Armstrong, 1998 Horwitz, 2000). 

According to Robinson (38), Whittaker and Feany (39), and Rice (5j, a great majority of secondary plant products are biosynthesized from acetate and shikimic acid (38), many of which have been implicated as allelopathic agents, and the main groups of compounds are described below. 

Arcmatic compounds phenols, phenolic acids, cinnamic acid derivatives, coumarins, flavonoids, quinones, and tannins, all of which are aromatic compounds, comprise the largest group of secondary plant products. They are often referred to as "phenolics" and have been identified as allelopathic agents in more instances than all of the other classes of compounds combined 5). 

AOPP has been used in many studies to examine the role of PAL in the synthesis of secondary aromatic compounds. The results summarized in Table I indicate that levels of AOPP that have little or no effect on growth can strongly affect production of secondary aromatic products. Other studies have shown rapid cessation of isoflavone synthesis in Cicer ariethinum by 0.3 mM AOPP (61). 

Many herbicides and other chemicals have been reported to influence levels of various phenolic compounds in higher plants by unknown mechanisms. It is unlikely that more than a few of these compounds have a primary influence on secondary phenolic compound synthesis. For instance, in our survey of the effects of 17 herbicides on anthocyanin accumulation, only glyphosate appeared to directly influence accumulation (31). The effects of several compounds on secondary phenolic compound production for which the mechanism of influence is unknown are summarized in Table II. A much longer list could be derived from the literature. Unfortunately, many of these compounds are phytotoxic or are known to have effects other than on secondary aromatic compound production. In most cases the effects on these compounds correlate well with extractable PAL activity (31, 71, 72, 73, 74) (Figure 5), even though they do not directly affect the enzyme. 

Chemical manipulation of secondary compound composition of crop plants offers several advantages over genetic control of their production. Chemical manipulation allows for timing the manipulation as well as possibly determining the quality and quantity of the desired response. 

Another field of research is the possibility offered by phytochemicals in protecting plants against diseases and pathogens (fungus, bacteria and nematodes). Numerous studies have suggested that plant-pathogen interactions are partially mediated via plant secondary metabolite production, despite the inconsistency revealed by some works on the ability of particular compounds to provide resistance to a specific pathogen. 

The chromatograms of the liquid phase show the presence of smaller and larger hydrocarbons than the parent one. Nevertheless, the main products are n-alkanes and 1-alkenes with a carbon number between 3 to 9 and an equimolar distribution is obtained. The product distribution can be explained by the F-S-S mechanism. Between the peaks of these hydrocarbons, it is possible to observe numerous smaller peaks. They have been identified by mass spectrometry as X-alkenes, dienes and also cyclic compounds (saturated, partially saturated and aromatic). These secondary products start to appear at 400 °C. Of course, their quantities increase at 425 °C. As these hydrocarbons are not seen for the lower temperature, it is possible to imagine that they are secondary reaction products. The analysis of the gaseous phase shows the presence of hydrogen, light alkanes and 1-alkenes. 

Refined, bleached, and deodorized oils may contain some nutritionally objectionable compounds - secondary oxidation products, di- and tri-enoic... 

Photolytic. The major photolysis and hydrolysis products identified in distilled water were pentachlorocyclopentenone and hexachlorocyclopentenone. In mineralized water, the products identified include cis- and /ra/3s-pentachlorobutadiene, tetrachlorobutenyne, and pentachloro-pentadienoic acid (Chou and Griffin, 1983). In a similar experiment, irradiation of hexachlorocyclopentadiene in water by mercury-vapor lamps resulted in the formation of 2,3,4,4,5-pentachloro-2-cyclopentenone. This compound hydrolyzed partially to hexachloroindenone (Butz et ah, 1982). Other photodegradation products identified include hexachloro-2-cyclopentenone and hexachloro-3-cyclopentenone as major products. Secondary photodegradation products reported include pentachloro-as-2,4-pentadienoic acid, Z- and A-pentachlorobutadiene, and tetrachloro-butyne (Chou et ah, 1987). In natural surface waters, direct photolysis of hexachlorobutadiene via sunlight results in a half-life of 10.7 min (Wolfe et al, 1982). 

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