Aquatic plant metabolism

Roy S, O Hanninen (1994) Pentachlorophenol uptake/elimination kinetics and metabolism in an aquatic plant Eichhornia crassipes. Environ Toxicol Chem 13 763-773. 

Recent reports on biosorbents based on diverse types of macrophytes are found widely in the literature. Free-floating aquatic plants from the genera Salvinia, Azolla, Eichhornia, Lemna, and Pistia have been described the most. S. natans biomass was able to uptake As(V) at low initial concentrations from 0.25 to 2 mg/L (74.8% and 54%, respectively). The experimental data fitted well to both Langmuir and Freundlich isotherms. The effect of pH and biomass quantities on sorption rate has also been investigated along with some metabolic parameters.105... 

Elevated accumulations occur in aquatic plants during exposure to 100 pg/L and in fish during exposure between 1 and 13 pg/L. All species in these groups, however, seemed unaffected by elevated body burdens, as judged by normal growth and metabolism. 

In crop protection as well, understanding plant metabolism is of paramount importance to increase selectivity and to address resistance of chemical compounds. Moreover, dissipation of a compound in the aquatic ecosystem is very similar to the excretion phenomena of the bodies. An extensive amount of evidence has been accumulated to support the involvement of CYPs in the metabolism and detoxification of herbicides, fungicides and insecticides. The understanding of their biotransformations at the molecular level may be extremely helpful for herbicide- or insecticide-synergistic development. 

Jahren et al, 2001). Today most C4 plants are tropical grasses, and most CAM plants are submerged aquatic plants and desert succulents. Most other kinds of plants use the C3 photosynthetic pathway. There is the potential to recognize these various metabolic pathways from the isotopic composition of organic carbon in paleosols and in fossil plants, and in the fossils of animals which ate the plants (Ceding et al, 1997 MacFadden et ah, 1999 Krull and Retallack, 2000). 

FIGURE 4.3 Variation of dissolved oxygen content of pond water with aquatic plants as affected by photosynthetic activity accompanying sunshine, and metabolic oxygen consumption during dark hours. Data plotted from Klein [13]. 

The modes of senescence, death, and degradation rates of biota are also of considerable importance to rates and pathways of degradation and energetic utilization. For example, the continual slow senescence and release of DOM from a higher aquatic plant is very different from the relatively instantaneous biochemical death and release of DOM from a bacterium or alga. Non-preda-tory death and metabolism of non-living detrital POM and DOM by prokaryotic and protistan heterotrophs dominate in all aquatic ecosystems. 

Pentachlorophenol is metabolized by the aquatic plant Eichhornia crassipes to a number of metabolites including di-, tri-, and tetra-chlorocatechol, 2,3,5-tri- and tetrachlorohydroquinone, pentachlo-roanisole, and tetrachloroveratrole (Roy and Hanninen 1994). The phenolic compounds should be compared with those produced during the photochemical (see Figure 4.4) and the initial stages in the microbiological metabolism of pentachlorophenol (Chapter 6, Section 6.5.1.2), followed by O-methylation (Section 6.11.4). 

Not much is known about mercury uptake and metabolism in wild plant species. However, accumulation of the metal has been observed in mushrooms and aquatic plants (Kabata-Pendias and Pendias, 1984). Most studies of agricultural crops, with Hg loads far greater than those encountered in normal conditions, demonstrate the tendency for mercury to accumulate in the roots (Steinnes, 1995). 

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