Plant tissue substrates

Ideally, the test chemical should be selectively removed from the plant without disturbing the remaining plant tissue. Sometimes this can be accomplished for chemicals on leaf surfaces (e.g., Dimock Kennedy 1983), but selective removal of internal leaf constituents usually is impossible. 

As an alternative to solvent, chemicals may be dissolved or suspended in warm (32°C) gelatin, which is then painted uniformly on the leaves (Wolfson Murdock 1987). The optimal gelatin concentration and other methodological factors may vary with both the insect to be tested and leaf surface characteristics of the particular plant species (Wolfson Murdock 1987). 

Leaf disks are more convenient than whole leaves because they are of uniform size and shape and can be easily arranged in behavioral arenas, such as petri dishes. While such care in controlling for size, shape, and position may be necessary to develop highly discriminating bioassays, preliminary experiments should be made to ensure that results using leaf disks are consistent with those using whole leaves. 

Even the size of leaf disks may affect the outcome of preference tests, as smaller disks have relatively more wounded edge tissue that may affect the suitability of center tissue more than for larger disks (Jones Coleman 1988). Leaf disks are not recommended for work with sucking insects. Physiological changes seem to affect the phloem contents very rapidly (e.g., Muller 1966 van Emden Bashford 1976) and may well induce a generally unsuitable condition. 

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Plant tissue Substrate VLCFA synthesis (nmol/ng prot/h) Sribcellular Heferenc locatioi ... 

It is of interest that the activation of POs often takes place in stomata guard cells, since P. infestans mainly penetrates into plant tissues through stomata slits. The localisation of phenolic compounds - some of them seemingly being used by POs as a substrate - and PO activity was visible in guard cells. (Maksimov et al., 2011). As such, the immune reaction occurred in close proximity to pathogen structures. 

Classical approaches to plant DNA isolation aim to produce large quantities of highly purified DNA. However, smaller quantities of crudely extracted plant DNA are often acceptable for PCR analysis. Another efficient method for preparation of plant DNA for PCR is a single-step protocol that involves heating a small amount of plant tissue in a simple solution. Several factors influence nucleic acid release from tissue salt, EDTA, pH, incubation time and temperature. These factors must be optimized for different sample substrates. EDTA in the sample solution binds the Mg + cofactor required by the Taq polymerase in the PCR, so the EDTA concentration in the solution, or the Mg + concentration in the PCR, must be carefully optimized. 

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. 

Along with electronic transport improvements must come attention to substrate transport in such porous structures. As discussed above, introduction of gas-phase diffusion or liquid-phase convection of reactants is a feasible approach to enabling high-current-density operation in electrodes of thicknesses exceeding 100 jxm. Such a solution is application specific, in the sense that neither gas-phase reactants nor convection can be introduced in a subclass of applications, such as devices implanted in human, animal, or plant tissue. In the context of physiologically implanted devices, the choice becomes either milliwatt to watt scale devices implanted in a blood vessel, where velocities of up to 10 cm/s can be present, or microwatt-scale devices implanted in tissue. Ex vivo applications are more flexible, partially because gas-phase oxygen from ambient air will almost always be utilized on the cathode side, but also because pumps can be used to provide convective flow of any substrate. However, power requirements for pump operation must be minimized to prevent substantial lowering of net power output. 

The preparation of extracts of plant tissue containing active DPOs can be fraught with problems. In the intact plant tissue, both enzyme and substrate are present but are thought to be compartmentalized, with the enzyme bound to membranes and the native substrate ) present in the vacuole. As soon as the tissue is disrupted, these can react together with the very real risk of a suicidal inactivation of the enzyme by its own reaction products. As a result, most isolation procedures for DPOs include additions of ascorbate and/or cysteine to prevent the formation of the reactive quinones. Assuming that the enzyme is... 

Examples of substrates released into the culture medium by plant tissue cultures are given in Table 7. The growth rate and yield can be improved by medium optimization. The products from plant tissue cultivations are either directly extracted from the cells or the medium or subjected to biotransformation and enzymatic synthesis. 

More knowledge of physical and chemical properties of pectic enzymes, their substrate specificity, pattern of action, action on plant tissues, interaction with each other and other polysaccharide degrading enzymes is essential to establish their technological roles and to improve existing applications and to develop new applications. 

Powerful enzyme hydroxylation systems of organic substrates, i.e. steroids, hydrocarbons, organic acids, alcohols and amines, are operatives in animal and plant tissues and bacteria (Coon et al., 1981 Guengerich and Mcdonald (1984) Weiner, 1986 Sono et al., 1996 Oriz de Montellano, 1995 Sono et al., 1996 Newcomb et al., 2000 Ogliaro et al., 2000, 2001 and references therein). These enzymes catalyze oxidation processes according to the following general scheme ... 

The substrates of the polyphenol oxidase enzymes are phenolic compounds present in plant tissues, mainly flavonoids. These include catechins, anthocyanidins, leucoantho-cyanidins, flavonols, and cinnamic acid derivatives. Polyphenol oxidases from different sources show distinct differences in their activity for different substrates. Some specific examples of polyphenolase substrates are chlorogenic acid, caffeic acid, dicatechol, protocatechuic acid, tyrosine, catechol, di-hydroxyphenylalanine, pyrogallol, and catechins. 

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