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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 89 (1993), S. 0 
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Leaves of 12-week-old tobacco plants (Nicotiana tabacum L. cv. Samsun NN) were infiltrated with suspensions of Pseudomonas syringae pv, pisi (DSM 50291) to induce hypersensitive reaction (HR). Cotyledons of 2-week-old cotton plants (Gossypium hirsutum L. cv. Acala 442 and Coker BR) were infiltrated with Xanthomonas campestris pv. malvacearum (race 10) to induce the disease. In tobacco, HR-related increases in NH+4 levels started within 2 h after infection and continued up to the time of tissue decay. Increase of NH+4 and especially K+ efflux were detected in intercellular washing fluids (IWF). Antibiotics stopped and later reverted NH+4 production and K+ efflux, but only if applied within 2 h after infection. When 10 mM NH+4 was injected into leaves, it was rapidly consumed from the IWF, and also, although more slowly, within the leaf cells. The concomitant K+ efflux was strong but delayed, and most of the K+ was reabsorbed after 2 h. Bacterial cell multiplication in HR stopped before the appearance of HR symptoms and cell necrosis. In the compatible reaction in cotton cotyledons, both NH+4accumulation and K+ efflux proceeded much more slowly than in the HR with tobacco, and bacteria continued to multiply until general cell necrosis occurred. The compatible reaction developed faster in constant darkness than in a light/dark rhythm. Bacterial enzymes produced NH+4, mainly from proteins of host cells, in both light and darkness. Continuous light delayed the main peak of both NH+4 production and K+ efflux. High CO2 concentration inhibited both processes, thus indicating that photorespiration plays a role in enhancing the release of free ammonium during bacterial pathogenesis. This is supported by shifts in the pattern of amino acids. The results demonstrate the accelerating and aggravating effect of ammonium in pathogenesis and HR, though ammonium is not the primary agent.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-2048
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Short time incorporation of 32P was carried out with synchronised algae (young cells) depleted of phosphate. For the separation and determination of the acid-insoluble phosphate fractions of the cells an improved fractionation procedure was applied. In order to exclude competition by carbon dioxide all experiments were done in the absence of CO2. Compared with nitrogen, CO2-free air produces an increase in the labelling of phosphorylated compounds in the light. In strong white light, at high pH, air effects a remarkable increase of 32P in the acid-insoluble phosphate (P u), mainly in inorganic polyphosphates (P ul), whereas the total phosphate uptake remains almost unchanged. The increase in labelling of acid-insoluble phosphate is, therefore, accompanied by a substantial decrease in the labelling of acid-soluble compounds (P l). In weak white light or in far-red light, at low pH even in strong white or red light, an increase of phosphate uptake and an increased labelling of the acid-stable organic acid-soluble fraction (P os) is observed instead. The effect of oxygen increases somewhat with increasing light intensity up to light saturation, and it increases markedly with increasing oxygen concentration. An essential contribution by oxidative phosphorylation to this oxygen effect can be ruled out on account of its much higher sensitivity to oxygen. Pseudocyclic photophosphorylation is also not regarded as the main force because of its higher oxygen affinity. Occurrence of photorespiration has not been clearly established so far in related algae (Chlorella), and its use for phosphorylation is unknown. A better, although not complete explanation is given by comparing the oxygen effect with the well-known inhibition of photosynthesis by oxygen (Warburg effect), which leads to an increase in glycolate formation and a simultaneous decrease in the pool sizes of carbon reduction cycle intermediates, even in the absence of CO2. Since the photophosphorylation process, as well as the photosynthetic electron flow, seem unaffected by high oxygen concentrations whereas the formation of organic phosphate compounds is partially inhibited, excess ATP may be available for polyphosphate synthesis. This explanation would be consistent with the assumption that polyphosphate-ADP kinase mediates an equilibrium between ATP and polyphosphates, mainly at higher pH. At low pH and in other cases the excess ATP might be available for an increased phosphate uptake and for phosphorylation of endogenous carbohydrates.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-2048
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The uptake of nitrate or nitrite in the light, the release of nitrite and ammonia, and the corresponding alkalinisation of the medium were measured in synchronous Ankistrodesmus braunii (Naeg.) Brunnth. The increase in the OH− concentration in the medium reflects a stoichiometric ratio between OH− and NO3 − of 1.3–1.8 in air, reaching almost 2.0 in CO2−free air or nitrogen. At low CO2 concentrations a large proportion of the nitrogen taken up as nitrate is released as ammonia, much less as nitrite. The stoichiometry of alkalinisation and NO3 − or NO2 − uptake can be quantitatively explained by assuming: 1) a counter-transport, at a ratio of 1:1, of OH− against NO3 − at the plasmalemma and of OH− against NO2 − at the chloroplast envelope, and 2) a co-transport of 1:1 of OH− and NH4 + to the medium through both membranes. The first OH− required is formed by proton consumption in nitrite reduction, the second OH− by proton consumption in the formation of NH4 + ions. Transport of K+, Na+ and Ca2+ is not or only scarcely involved. This proposed transport system could provide charge equilibrium between inside and outside the cells and could enable the cells to avoid nternal pH changes in nitrate and nitrite reduction.
    Type of Medium: Electronic Resource
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