Accumulation of secondary products

Manipulation of the culture environment has proved successful in many cases, stimulating the accumulation of secondary products in plant cell cultures, but each treatment will not always be successful with every culture [21, 23, 28, 29]. A range of treatments may have to be tried for each individual culture. All the changes in growth conditions and medium have perhaps a common feature in that they all cause some form of stress. Stress is known to trigger changes in cells and this may stimulate the accumulation of secondary products (Fig. 25.4). 

It will be noted that nitrogen atoms are a good example of atoms the disappearance of which is hindered by untreated molybdenum.44 Calculated data and simple considerations show that the curve for accumulation of secondary products yielded by a reaction of primary radicals with molecules is not different from the primary product curve. This is due to the fact that only one oxygen atom participates in the formation of secondary products. Since the reactivity of a primary radical is such that it is converted into a stable molecule before reaching the trap, its presence may be detected. It will be noted also that while the limiting concentrations of primary and secondary products (when these are the only ones) are equal to the initial concentration atoms, the maximum concentrations of quadratic and cubic products are not higher than one-half and one-third, respectively, of this concentration. 

Yeoman MM, Lindsey K, Miedzybrodzka HB, McLauchlan WR. Accumulation of secondary products as a facet of differentiation in plant cell cultures. In Yeoman MM, Truman DES, editors. Differentiation in Vitro. London Cambridge University Press 1980. p. 65-82. 

The accumulation of secondary products is in most plants and microorganisms an important means for survival, which in several respect is equivalent to the mobility of most animals it deters potential predators, attracts pollinators (corresponding to sexual mates), discourages competing species etc. (E 5). 

The chiral synthesis of allylic alcohols has been the focus of many research works due to the high versatility of these molecules in the preparation of many active com-poimds [58,82], Allen and Williams reported the first example of DKR of allylic alcohols via lipase-palladium catalyst coupling deracemization of cyclic allylic acetates [83]. However, the accumulation of secondary products, as well as the long reaction times required, limited the use of this strategy. 

The 4-coumarate CoA ligase (4CL EC 6.2.1.12) enzyme activates 4-coumaric acid, caffeic acid, ferrulic acid, and (in some cases) sinapic acid by the formation of CoA esters that serve as branch-point metabolites between the phenylpropanoid pathway and the synthesis of secondary metabolites [46, 47]. The reaction has an absolute requirement for Mg " and ATP as cofactors. Multiple isozymes are present in all plants where it has been studied, some of which have variable substrate specificities consistent with a potential role in controlling accumulation of secondary metabolite end-products. Examination of a navel orange EST database (CitEST) for flavonoid biosynthetic genes resulted in the identification of 10 tentative consensus sequences that potentially represent a multi-enzyme family [29]. Eurther biochemical characterization will be necessary to establish whether these genes have 4CL activity and, if so, whether preferential substrate usage is observed. 

There is also strong evidence indicating that there is an inverse relationship between growth rate and secondary metabolite production (Lindsey and Yeoman, 1983). When growth is intense, the primary processes of the cell are cell division and production of cell mass. In the stationary phase, when growth is minimal, conditions favor the production and accumulation of secondary metabolites. 

The presence or absence of phosphate ions plays an important role in the expression and accumulation of some secondary products. Zenk et al. (47) have demonstrated a 50% increase in anthraquinone accumulation in cell cultures of Morinda citrofolia when phosphate was increased to a concentration of 5g7h In suspension cultures of Catharanthus roseus, the overall accumulation of secondary metabolites like tryptamine and indole alkaloids has been shown to occur rapidly when cells were shifted to a medium devoid of phosphate (48,49). A study on the uptake of phosphate and its effect on phenylalanine ammonia lyase and the subsequent accumulation of cinnamoyl putrescine in cell suspension cultures of Nicotiana tabacum demonstrated marked sensitivity to phosphate concentration (5DX Enhanced phenylalanine ammonia lyase activity and increased production of cinnamoyl putrescine was induced by subculture onto phosphate-free medium while suppression of these effects and stimulation of growth was observed with phosphate concentrations of 0.02-0.5uM. Interestingly, phenylalanine ammonia lyase activity is stimulated by increasing phosphate concentrations in cell suspension of Catharanthus roseus (51). 

Another consequence of increased weathering is the accumulation of weathering products, (i.e., Fe and Al oxides) close to the root surface (Courchesne and Gobran, 1997 Martin et al., 2004). These secondary minerals, alone or in combination with organic matter, increase the potential cation- (CEC) or anion-exchange (AEC) capacity of the rhizosphere materials (Gobran and Clegg,... 

Renal tubular acidosis can be classified into two main types, type I and type II, which are hereditary (11). Renal tubular acidosis can also result from accumulation of waste products, including a variety of metabolic acids in uremia. Another type of renal tubular acidosis, type IV, is due to hyporeninemic hypoaldostero-nism. Hypoaldosteronism appears to be secondary to the inability of the kidney to... 

Within the ODZ, nitrous oxide (N20), another major intermediate of denitrification (and a byproduct of nitrification), shows a trend of variability quite different from that of N02 (Fig. 6.15), but similar to that observed in the ODZs of the Pacific Ocean (Codispoti Christensen, 1985). That is, N20 concentration generally increases non-linearly with the depletion in 02 until the environment turns reducing thereafter, concomitant with the accumulation of secondary N02, a rapid fall in N20 concentration takes place. Accordingly, the SNM is characterized by a minimum in N20 concentration (<10nM), whereas the oxic-suboxic interfaces are characterized by peak N20 levels exceeding 50nM (Law Owens, 1990 Naqvi Noronha, 1991). Attempts have been made to evaluate the relative importance of nitrification, denitrification and coupling between the two processes as pathways for N20 production by... 

The use of higher plants and their preparations to treat infections is an age-old practice and in times past possibly the only method available. Interest in plants with antimicrobial properties has revived because of the current problems associated with the use of penicillin and other antibiotics. Therapy with several types of antibiotics is frequently accompanied by side effects and microbial resistance. It is currently accepted that the accumulation of secondary metabolites in plants can be a consequence of requirements for chemical defense against microorganisms. Research carried out in the chemical and biological sciences has resulted in much evidence concerning the defensive role of natural products. 

Ikemeyer, D. and W. Barz Comparison of secondary product accumulation in photoautotrophic, photomix-otrophic and heterotrophic Nicotiana tabacum cell suspension cultures Plant Cell Rept. 8 (1989) 479-482. 

It should be noted that Reaction A is an H-abstraction, and thus it is usually reversible. In contrast. Reaction B is not readily reversible after the RO and 0H radicals escape from the solvent cage. The net result of both Reactions A and B is the formation of secondary products and the generation of additional radicals. Figure 2 outlines the progress of a hypothetical autoxidation of a lipid. The initiation phase is followed by rapid accumulation of radicals that promote both the formation and destruction of hydroperoxides. Finally, radical combination (termination) leads to nonradical secondary products. As discussed later, both secondary products and radical reactions per se are involved in food deterioration. 

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