Resistance chloroplast

Van Oorschot, J.C. (1991). Chloroplastic resistance of weeds to triazines in Europe. In J.C. Caseley, G.W. Cussans and R.K. Atkin, eds., Herbicide Resistance in Weeds and Crops. Boston Butterworth-Heinemann, pp. 87-102. 

As indicated in Figure 8-8, five additional resistances are involved in CO2 movement compared to water vapor movement. The new components of the pathway are the nongaseous (i.e., liquid phase) parts of the cell wall of a mesophyll cell (resistance = r ), a plasma membrane (r ), the cytosol (r X the chloroplast limiting membranes (r ), and the interior of the chloroplasts (r ). For convenience we will divide these five resistances into two parts, the mesophyll resistance, and the chloroplast resistance,... 

McNally, S., P. Bettini, M. Sevignac, H. Darmency, J. Gasquez, and M. Dron. 1987. A rapid method to test for chloroplast DNA involvement in atrazine resistance. Plant Physiol. 83 248-250. 

Polyphenol oxidase occurs within certain mammalian tissues as well as both lower (46,47) and higher (48-55) plants. In mammalian systems, the enzyme as tyrosinase (56) plays a significant role in melanin synthesis. The PPO complex of higher plants consists of a cresolase, a cate-cholase and a laccase. These copper metalloproteins catalyze the one and two electron oxidations of phenols to quinones at the expense of 02. Polyphenol oxidase also occurs in certain fungi where it is involved in the metabolism of certain tree-synthesized phenolic compounds that have been implicated in disease resistance, wound healing, and anti-nutrative modification of plant proteins to discourage herbivory (53,55). This protocol presents the Triton X-114-mediated solubilization of Vida faba chloroplast polyphenol oxidase as performed by Hutcheson and Buchanan (57). 

Plant susceptibility to ozone as determined by visible injury may be very closely related to quantities of o-diphenols associated with the chloroplasts and specific requirements for activation of polyphenol oxidase enzymes. There is a significant correlation between ozone injury and concentrations of total phenols expressed as percent caffeic acid equivalents in peanut cultivars. This concept is not intended to underestimate the importance of membranes that separate phenols and enzymes. Perhaps future research will demonstrate that membranes of resistant alfalfa, green bean and other species differ both qualitatively and quantitatively from those of susceptible plants of these species. 

The selection of transformed chloroplasts usually involves the use of an antibiotic resistance marker. Spectinomycin is used most routinely because of the high specificity it displays as a prokaryotic translational inhibitor as well as the relatively low side effects it exerts on plants. The bacterial aminoglycoside 3 -adenyltransferase gene (ciadA) confers resistance to both streptomycin and spectinomycin. The aadA protein catalyzes the covalent transfer of an adenosine monophosphate (AMP) residue from adenosine triphosphate (ATP) to spectinomycin, thereby converting the antibiotic into an inactive form that no longer inhibits protein synthesis for prokaryotic 70S ribosomes that are present in the chloroplast. 

This evidently accounts for the presence of isoprene in the breath.34 Isoprene is also formed by many plants and is released into the atmosphere in large amounts, which contribute to photochemical formation of haze. A Mg2+-dependent enzyme catalyzes the elimination of pyrophosphate.35 Isoprene emissions rise with increasing temperature, and it has been suggested that the isoprene may dissolve in chloroplast membranes and in some way confer increased heat resistance.36 37 Hydrolytic dephosphorylation can lead to dimethylallyl alcohol, which is oxidized in the liver to dimethy-lacrylyl-CoA (Eq. 22-1). 

In a study designed to determine the mode of action of atrazine in higher plants, Shimabukuro and Swanson (1969) concluded that atrazine inhibits the Hill reaction and its noncyclic phosphorylation, while being ineffective against cyclic photophosphorylation. Atrazine readily penetrated the chloroplast of resistant as well as susceptible plants. In tolerant plants such as sorghum, the metabolism of atrazine was postulated to occur outside the chloroplasts to form water-soluble and insoluble residues that reduced the concentration of photosynthetic inhibitors in the chloroplasts. 

Gardner, G. (1981). Azidoatrazine Photoaffinity label for the site of triazine herbicide action in chloroplasts. Science, 211 937-940. Gingrich, J.C., J.S. Buzby, V.L. Stirewalt, and D.A. Bryant (1988). Genetic analysis of two new mutations resulting in herbicide resistance in the cyanobacterium Synechococcus-sp pcc 7002. Photosyn. Res., 16 83-100. 

Burke, J.J., R.F. Wilson, and J.R. Swafford (1982). Characterization of chloroplasts isolated from triazine-susceptible and triazine-resistant biotypes of Brassica campestris L. Plant Physiol., 70 24—29. 

Chapman, D.J., J. De Felice, and J. Barber (1985). Characteristics of chloroplast thylokoid lipid composition associated with resistance to triazine herbicides. Planta, 166 280-285. 

Lehoczki, E., E. Polos, G. Laskay, and T. Farkas (1985). Chemical compositions and physical states of chloroplast lipids related to atra-zine resistance in Conyza canadensis L. Plant Sci., 42 19-24. 

Soon after the discovery of triazine-resistant common groundsel, another equally important discovery was made. Radosevich and DeVilliers (1976) found that the mechanism of resistance in this weed was due to insensitive chloro-plasts that were capable of photosynthesis, even in the presence of simazine or atrazine. This was surprising because earlier research had confirmed that there were no differences in plant selectivity or susceptibility due to the origin of chloroplasts. Moreland (1969) had reported that isolated chloroplasts were equally inhibited to simazine whether they came from tolerant com or susceptible spinach. Radosevich and Appleby (1973) had confirmed there were no differences between the susceptible and resistant biotypes of common groundsel due to herbicide uptake, distribution, or metabolism, whereas it is known that com metabolizes triazine herbicides (Shimabukuro, 1985). 

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