Distribution within the Plant

Flavonoids, when present in trees, are likely to be found equally in sapwood, heartwood, and bark, but the amounts in the different tissues may vary considerably. Heartwood is usually a better source than sapwood, the amounts present reaching up to 0.5% to 1% dry weight. Bark tissues may contain larger amounts. 

For example, Douglas-fir bark, Pseudotsuga menziesii, contains up to 5% dihydroquercetin (85) whereas bark of Firms contorta contains between 0 and 2% myricetin (83). Angiosperm barks seem to have rather lesser amounts the recovery of quercetin (8) from bark or Quercus tinctoria of Q phellus does not usually exceed 0.5%. 

The compounds found in the different parts of the wood also show significant differences in those cases in which comparisons have been made. While the pattern in the heartwood usually mirrors that in the sapwood, that of the bark often diverges. In the genus Moms, for example, the heartwood contains mixtures of dihydroflavonols (up to 0.03% dry wt) and flavonols (about 0.01% total), while the bark contains isopentenylflavones in yield up to 0.2% total (38). In Prunus, there is some overlap between heartwood and bark components, but the heart-wood is generally richer in structural types. In Prunus avium, for example, there 

Heartwood flavonoids are usually present in the free state, though it is possible that they may be loosely associated with other wood components. In the case of Artocarpus heartwood, it appears that at least some of the flavonol morin is present as a calcium chalate (29). Since most heartwood flavonoids have the ability to chelate metals, this may happen in other cases too. 

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A. A. Meharg and K. Killham, Carbon distribution within the plant and rhizosphere for Lolium perenne subjected to anaerobic soil conditions. Soil Biol. Biochem. 22 643 (1990). 

In spite of the common mode of action, many other factors are significant for the successful use of individual azole compounds either for control of plant diseases or in the treatment of mycoses. Apart from the nature of the infection, the infection pressure, climatic conditions, the uptake of the fungicide by the plant, its transport and distribution within the plant, and plant compatibility are all important criteria in the complex interaction between pathogen, plant and fungicide. In medicine, high activity, good tolerance and optimal pharmacokinetic properties are prerequisites for therapeutic utility. 

The two main pathways for the uptake of toxic substances by plants are through their root systems and across their leaf cuticles. Stomata, the specialized openings in plant leaves that allow carbon dioxide required for photosynthesis to enter the leaves and oxygen and water vapor to exit, are also routes by which toxic substances may enter plants. The mechanisms by which plants take up systemic pesticides and herbicides, which become distributed within the plant, have been studied very intensvively. 

Taxane alkaloids have a very limited distribution within the plant kingdom, and occur only in two genera of the yew family (Taxus and Austrotaxus). The genus Austrotaxus is monotypic (A. spicata Compt), but contusion exists on the systematics of the genus Taxus, especially as regards the taxonomic status of certain Asian yews. Reference will be given here to the Krttssmann classification (Table 1) [28]. 

Darrah, P. R., and Staunton, S. (2000). A mathematical model of root uptake incorporating root turnover, distribution within the plant and recycling of absorbed species.TJwr. J. Soil Sci. 51, 643-653. 

Gross, M., E. Lewinsohn, Y. Tadmor, E. Bar, N. Dudai, Y. Cohen, and J. Eriedman. 2009. The inheritance of volatile phenylpropenes in bitter fennel Foeniculum vulgare Mill. var. vulgare, Apiaceae) chemotypes and their distribution within the plant. 37 308-316. 

As discussed in the preceding section, the formation of unique species-specific PA patterns is achieved in two consecutive steps (i) synthesis of the backbone structure and (ii) its structural diversification. From a biochemical point of view there are two additional important metabolic features PAs do not undergo any degradation or turnover and they are slowly but steadily distributed within the plant. These features have been intensively studied with Senecio roots cultures... 

In addition to various studies on protein composition and distribution within the plant tissue [72], the influence of protein secondary structure on global crop attributes, such as nutritive values, baking quality, or digestive behavior, achieved increasing interest. 

Contaminant attenuation mechanisms involved in phytoremediation are complex and not limited only to the direct metabolism of contaminants by plants. Certain indirect attenuation mechanisms are implicated in phytoremediation, such as the metabolism of contaminants by plant-associated microorganisms, and plant-induced changes in the contaminated environment. In terrestrial species, transport of contaminants to the plant is dominated by uptaking water by roots, and distribution within the plant relies on xylem or phloem transport (Macek et ak, 2000). Various terms, reflecting each specific attenuation mechanism, have been extensively used to better describe specific applications of phytoremediation. These include phytoextraction, phytodegradation, phytotransformation, phytovolatilization and rhizodegradation (Burken and Ma, 2006). 

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