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Turfgrass Diseases and Nematodes
Published in L.B. (Bert) McCarty, Golf Turf Management, 2018
Bacteria are microscopic, single-celled organisms with rigid cell walls but no organized nucleus (termed prokaryotes). Fungi and Stramenopiles are eukaryotes, meaning they have organized nuclei within their cells. Bacteria reproduce by fission (or simple cell division), and can rapidly reproduce. They lack chlorophyll and overwinter, like fungi, in and on thatch, plants, seed, soil, and sometimes in insects. Bacterial pathogens enter plants only through wounds (which may be made by living organisms, such as insects) or natural openings, such as lenticels, hydathodes, or stomata. Although some bacteria are able to swim, splashing water, wind-blown water, insects, infected tools, or plant cuttings are the normal means of dispersal. Once inside the host, bacteria cause damage by producing toxins or by blocking vascular tissue. This blocking retards water movement and infected plants wilt. Practically all plant-infecting bacteria are rod shaped.
Xenobiotic metabolism and transport in Caenorhabditis elegans
Published in Journal of Toxicology and Environmental Health, Part B, 2021
Jessica H. Hartman, Samuel J. Widmayer, Christina M. Bergemann, Dillon E. King, Katherine S. Morton, Riccardo F. Romersi, Laura E. Jameson, Maxwell C. K. Leung, Erik C. Andersen, Stefan Taubert, Joel N. Meyer
A simple cell membrane consists of a lipid bilayer composed primarily of phospholipids, glycolipids, and cholesterol. The phospholipids arrange in such a way that their hydrophobic tails are pointed inwards and their hydrophilic heads are oriented toward the outer and inner membrane surfaces. The membrane barrier is differentially permeable to various xenobiotics based upon their physicochemical properties (movement by transporters is addressed below). Some xenobiotics might passively diffuse across cell membranes; hydrophilic molecules might enter through aqueous pores in the membrane, and hydrophobic molecules might diffuse directly through the lipid domain of the membrane (Benz, Janko, and Läuger 1980). The smaller the molecule, the more rapidly it moves across a membrane, either by aqueous pores or simple diffusion. For large organic molecules, the octanol/water partition coefficient P dictates the rate at which the molecule moves across the membrane, with higher lipophilicity (positive log P) corresponding to higher membrane permeability, except at extreme levels of lipophilicity. In the case of weak organic acids and bases, ionic compounds move slowly and inefficiently through aqueous pores whereas non-ionized forms diffuse across the lipid membrane. Thus, the rate at which non-ionized organic acids and bases permeate the membrane depends on pKa/pKb of the compound and the pH of the surrounding environment (Avdeef 2001; Klaassen 2019; Manallack et al. 2013). However, C. elegans is not just a simple cell model system with a single membrane for protection; it is a complex organism with many physical barriers that prevent the passive transport of molecules into its body. In this section, the physical barriers that may impact uptake and release of xenobiotics by C. elegans are presented (Figure 2).