Microbial plant tissues

That compounds of the potency of liriodenine are present in plant tissues underscores the potential of plants to affect dramatically other organisms in their environment. Release of liriodenine or similarly potent agents from decomposing plant materials may significantly modify the microbial flora of the root zone. This in turn may have direct and indirect effect the plants which will germinate and grow in the affected soil, the classical allelopathlc effect (11). 

Disruption of microbial cells (and, indeed, some animal/plant tissue types) is most often achieved by mechanical methods, such as homogenization or by vigorous agitation with abrasives. 

Figure 6.5 Diagrammatic representation of a cell homogenizer. This represents one of a number of instruments routinely used to rupture microbial cells, and in some cases animal/plant tissue...

Wang, D.S., R.W. Weaver, and J.R. Melton. 1984. Microbial decomposition of plant tissue contaminated with arsenic and mercury. Environ. Pollut. 34A 275-282. 

All of the principles and ideas covered in the previous section may be translated directly to the use of microorganisms as tools in the production of compounds of plant biosynthetic or biodegradative importance. Just as one finds microbial systems to be of value in preparing metabolites in mammalian systems, it may be possible to use microbial transformations to prepare derivatives of alkaloids that might be found rarely or only in very small quantities in plants. In this way, abundant prototype alkaloids may be used as microbial transformation substrates to provide a range of metabolites. As in the mammalian case, metabolism studies using plant tissues, tissue cultures, or cell-free extracts may be conducted in parallel with microbial metabolic systems. Metabolites common to both would be prepared in quantity by relatively simple fermentation scale-up methods. 

While most alkaloids do not contain aldehydes when they enter mammalian, microbial, or plant tissues, this functional group may become important when formed as a metabolite of alcohols (via alcohol dehydrogenase) or amines (via oxidative dealkylation and oxidative deamination). Aldehyde dehydrogenases catalyze oxidation of aldehydes to the corresponding carboxylic acids. The physical properties, catalytic mechanism, and specificity of this group of enzymes has been reviewed (99). The general reaction catalyzed by aldehyde dehydrogenase is seen in Eq. (9). 

The chemical synthesis of natural flavours started some time ago with the synthesis of coumarin in 1868 and vanillin in 1874 [7]. The development of the petrochemical industry and the availability of cheap oil has meant that most of the plant-derived products are now synthesised from crude oil. In addition, flavours can now be produced using microbial cultures. Thus, to achieve sustainable development plants will have to provide many of the products currently produced from petrochemicals, including flavours. In this chapter the possible use of plant tissue culture techniques and processes in the sustainable production of flavours is outlined and discussed. 

The biochemicals identified as allelochemicals are generally metabolites resulting from secondary plant and microbial metabolism. The levels of such compounds can be elevated in plant tissues by stress (temperature, nutrient, water stress) or as a response to pathogenic infections. Because of this, care needs to... 

The design and operation of a bioreactor are mainly determined by biological needs and engineering requirements, which often include a number of factors efficient oxygen transfer and mixing, low shear and hydrodynamic forces, effective control of physico-chemical environment, easy scale-up, and so on. Because some of these factors can be mutually contradictory, it is difficult to directly employ a conventional microbial reactor to shear-sensitive plant tissue cultures. 

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