Secondary compound accumulation

Secondary Compound Accumulation in Plants—The Application of Plant Biotechnology to Plant Improvement... 

Fester, T., W. Maier et al. (1999). Accumulation of secondary compounds in barley and wheat roots in response to inoculation with an arbuscular mycorrhizal fungus and co-inoculation with rhizosphere bacteria. Mycorrhiza 8(5) 241-246. 

Our investigations showed that in mixed melts of eutectic composition carbamide-NH4(K)Cl, the oxidation and reduction of melt constituents take place mainly independently of each other. The anodic process at platinum electrodes in the range of potentials below 0.9V is associated with the direct oxidation of carbamide to secondary and tertiary amide compounds, accumulation of ammonium ions in the melt, and evolution of the same gaseous products as in carbamide electrolysis [8], The cathodic process is accompanied by the formation of ammonia, CO, and C02, i.e. of the same products as in pure- carbamide electrolysis. In contrast to carbamide melt, a large amount of hydrogen appears in the cathode gases of the mixed melt, and in the anode gases of the carbamide-KCl melt, the presence of chlorine has been established at potentials above 0.9V. In the... 

The effect of phosphate on alkaloid production has also been evaluated (138). Using a modified induction medium devoid of phosphate and other essential growth factors, production of secondary compounds was more rapid than when phosphate was present. A broader study of the phenomenon has been reported by a French group (139) where, using three alkaloids as markers, the disappearance of the major nutrients from the medium and the evolution of phosphates, nitrates, ammonium ions, glucose, and starch in the cells were observed over time. It was not possible to relate alkaloid accumulation to the appearance or disappearance of any one metabolite in particular. However, other workers have found that the rate of biomass accumulation was directly related to the rate of formation of cellular serpentine (40) (140). 

There are a number of possibilities for using plant secondary chemistry to control herbivory in crop plants. One possibility is to select for insect resistant lines and though it has been done in only a few cases, select for specific allomones. There are, however, some potential problems with this approach. There is a cost for the production of the secondary compounds which may be useful for defense ( ). Insect resistant soybean cultivars produce lower yields of seeds and accumulate nitrogen at a slower rate than insect susceptible varieties in the absence of herbivores 3 ). Conversely, varieties of crop plants selected for high yield are often more susceptible to insects, pathogens, and weeds (35). 

Several trophic levels must be considered. Breeding plants with greater allomone content in some cases causes specialist herbivores to accumulate higher levels of these compounds and discourages parasites that normally control herbivore levels (36). The presence of secondary compounds may also alter the usefulness of the crop plant to man or his domestic animals. Lines of cotton with high gossypol content have increased insect resistance with regard to a nunter of insects, but have reduced value as food materials for livestock. 

Peipp H., Maier W., Schmidt J. Wray V. Strack D. Arbuscular mycorrhizal fungus-induced changes in the accumulation of secondary compounds in barely roots. Phytochemistry 1997 44 581-587. 

Secondary metabolites include essential oils, used in the flavour and fragrance industries. Essential oils are found in over 50 plant families and represent terpenoids and other aromatic compounds accumulating typically at relatively low concentrations (usually <1% of fresh weight, but can be up to 20%), but which have useful antimicrobial activity (Biavati el a/., 2003). Production of essential oils by plants is affected by many factors influencing plant growth. 

The production of toxins is only one aspect of plant defense strategy. As a result of the persistent battle of plants and herbivores, many optimized phenotypes have evolved, such as the preferential accumulation of alkaloids in tissues with a pattern that is consistent with predictions of optimal defense theory,65 i.e., the defense metabolites are allocated preferentially to tissues with a high probability of attack.66 The inducibility of pathways leading to plant secondary compounds as a strategy to minimize the costs of plant defense is a result of permanent optimization. One of a few examples of inducible alkaloid biosynthesis is the different Nicotiana species that exhibit dramatic wound-induced increases of nicotine, nomicotine, or anabasine.67... 

When plants undergo various stresses, certain secondary metabolites, including defense compounds, accumulate. Several secondary metabolites such as terpenoid indole alkaloids, indole glucosinolate, nicotine alkaloids, and polyamines are known to accumulate through the induction of biosynthetic genes by jasmonates.898-900 MeJA also induces genes involved in the formation of tryptophan derivatives, terpenoid indole alkaloids.901 These compounds are known to be involved in defense response to pathogen attack as phytoalexins. 

The biosynthesis of SM exhibits a remarkable complexity. Enzymes are specific for each pathway and are highly regulated in terms of compartmentation, time and space. The same is true for fhe mechanisms of accumulation or the site and time of storage. In general, we find fhaf fissues and organs which are important for survival and multiplication, such as epidermal and bark tissues, flowers, fruits and seeds, have distinctive profiles of SM, and secondary compounds are stored in high amounts in them. As an example, the complex pattern of alkaloid synfhesis, transporf and sforage is illustrated in Fig. 1.7. 

J. M. Widholm,in F. Constabel and I. K. Vasil (Eds), Cell culture and somatic cell genetics of plants 4. Selection of mutants which accumulate desired secondary compounds. Academic Press, San Diego, 1987, pp. 125-137. 

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