Plant metabolic pathways

Morgan, J.A. and Rhodes, D., Mathematical modeling of plant metabolic pathways, Metabol. Eng. 4, 80, 2002. 

Fig. 1. Modification of plant metabolic pathways for the synthesis of poly(3HB) and poly(3HB-co-3HV). The pathways created or enhanced by the expression of transgenes are highlighted in bold, while endogenous plant pathways are in plain letters. The various transgenes expressed in plants are indicated in italics. The ilvA gene encodes a threonine deaminase from E. coli. The phaARe, phaBRe, and phaCRe genes encode a 3-ketothiolase, an aceto-acetyl-CoA reductase, and a PHA synthase from R. eutropha, respectively. The btkBRe gene encodes a second 3-ketothiolase isolated from R. eutropha which shows high affinity for both propionyl-CoA and acetyl-CoA [40]. PDC refers to the endogenous plant pyruvate dehydrogenase complex...

Fig. 4. Modification of plant metabolic pathways for the synthesis of poly(3HAMCL) in peroxisomes. The pathways created or enhanced by the expression of transgenes (P. aeruginosa PHA synthase and C. lanceolata decanoyl-ACP thioesterase) and of mutant alleles of plant fatty acid desaturase genes are highlighted by bold arrows and the enzymes involved underlined...

Hrazdina, G. and Jensen, R.A., Spatial organization of enzymes in plant metabolic pathways, Annu. Rev. Plant Physiol Plant Mol. Biol, 43, 241, 1992. 

The gene technology developed in the past few decades can be used to test scientific hypotheses and to alter plant metabolic pathways for commercial advantage. These two uses of technology go hand in hand unless it is understood how a pathway works, it is very difficult to change that pathway in a particular direction. 

ROS interfered with plant metabolic pathways (including DNA and RNA synthesis), thus affecting normal redox reaction, leading to weakening of metabolism. 

Class III peroxidases have been the subject of numerous studies [10] and applications [11], since their extraordinary catalytic properties make them a valuable catalytic tool in the plant cell chemical factory, and in organic synthesis. In fact, class III peroxidases, together with other oxidative enzymes, such as cytochrome P450s and oxygenases [12], appear to be the main driving force in the evolution of plant metabolic pathways because individual enzymes can typically accept multiple substrates and form several products. This metabolic plasticity of class III peroxidases, paradoxically, has frequently led to misunderstanding of its vital function in the plant cell biochemical factory. 

Depending on concentration, herbicides may inhibit many different plant metabolic pathways in vitro as well as in vivo. However, often the relevance of an inhibitory activity in vitro for the action on the intact growing plant is not clear. Trifluralin and chlorpropham e.g. affect chloroplast and mitochondrial activities in vitro (J ). In the field, however, they inhibit the growth of seedlings and provoke characteristic morphological responses which can not be traced to the effects on the organelles mentioned above. A simple test system more closely reflecting the primary sensitive pathway under field conditions would therefore clearly be helpful. 

FIGURE 7.4 Plant metabolic pathways in the presence and absence of oxygen. 

It is expected that the biosynthetic capacity of plants could be exploited in vitro using plant cells and cell tissue systems, analogous to microbial cells in fermentation processes. An important requirement for the improvement of secondary metabolite synthesis is an understanding of the metabolic pathways and the enzymology of the biosynthesis of particular products. The knowledge of plant metabolic pathways is still very limited. It needs more in-depth study by biologists, which will help to make the chemical bioengineering more practical. 

Oksman-Caldentey, K.-M., Saito, K. (2005) Integrating genomics and metabolomics for engineering plant metabolic pathways. Current Opinion in Biotechnology, 16, 174-179. 

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