Home About us Contact
|
Home About us Contact | ||
|
|
||
H+ Efflux (h+ + efflux)
Selected AbstractsK+ influx by Kup in Escherichia coli is accompanied by a decrease in H+ effluxFEMS MICROBIOLOGY LETTERS, Issue 1 2001Ella Zakharyan Abstract Escherichia coli accumulates K+ by means of multiple uptake systems of which Kup is the major transport system at acidic pH. In cells grown under fermentative conditions at pH 5.5, K+ influx by a wild-type strain upon hyper-osmotic stress at pH 5.5 was accompanied by a marked decrease in H+ efflux, with a 1:1 ratio of K+ to H+ fluxes. This was observed with cells treated with N,N,-dicyclohexylcarbodiimide. Similar results with a mutant defective in Kdp and TrkA but with a functional Kup system but not in a mutant defective in Kdp and Kup but having an active TrkA system suggest that Kup operates as a H+,K+ -symporter. [source] pH regulation in an acidophilic green alga , a quantitative analysisNEW PHYTOLOGIST, Issue 2 2009Birgit Bethmann Summary ,,Short-term cytosolic pH regulation has three components: H+ binding by buffering groups; H+ transport out of the cytosol; and H+ transport into the vacuole. To understand the large differences plants show in their tolerance to acidic environments, these three components were quantified in the acidophilic unicellular green alga Eremosphaera viridis. ,,Intracellular pH was recorded using ion-selective microelectrodes, whereas constant doses of weak acid were applied over different time intervals. A mathematical model was developed that describes the recorded cytosolic pH changes. Recordings of cytosolic K+ and Na+ activities, and application of anion channel inhibitors, revealed which ion fluxes electrically compensate H+ transport. ,,The cytosolic buffer capacity was , = 30 mM. Acidification resulted in a substantial and constant H+ efflux that was probably driven by the plasmalemma H+ -ATPase, and a proportional pH regulation caused by H+ pumped into the vacuole. Under severe cytosolic acidification (, 1 pH) more than 50% of the ATP synthesized was used for H+ pumping. While H+ influx into the vacuole was compensated by cation release, H+ efflux out of the cell was compensated by anion efflux. ,,The data presented here give a complete and quantitative picture of the ion fluxes during acid loading in an acidophilic green plant cell. [source] A comparison of ammonium, nitrate and proton net fluxes along seedling roots of Douglas-fir and lodgepole pine grown and measured with different inorganic nitrogen sourcesPLANT CELL & ENVIRONMENT, Issue 3 2008B. J. HAWKINS ABSTRACT Significant spatial variability in NH4+, NO3, and H+ net fluxes was measured in roots of young seedlings of Douglas-fir (Pseudotsuga menziesii) and lodgepole pine (Pinus contorta) with ion-selective microelectrodes. Seedlings were grown with NH4+, NO3,, NH4NO3 or no nitrogen (N), and were measured in solutions containing one or both N ions, or no N in a full factorial design. Net NO3, and NH4+ uptake and H+ efflux were greater in Douglas-fir than lodgepole pine and in roots not exposed to N in pretreatment. In general, the rates of net NH4+ uptake were the same in the presence or absence of NO3,, and vice versa. The highest NO3, influx occurred 0,30 mm from the root apex in Douglas-fir and 0,10 mm from the apex in lodgepole pine. Net NH4+ flux was zero or negative (efflux) at Douglas-fir root tips, and the highest NH4+ influx occurred 5,20 mm from the root tip. Lodgepole pine had some NH4+ influx at the root tips, and the maximum net uptake 5 mm from the root tip. Net H+ efflux was greatest in the first 10 mm of roots of both species. This study demonstrates that nutrient uptake by conifer roots can vary significantly across different regions of the root, and indicates that ion flux profiles along the roots may be influenced by rates of root growth and maturation. [source] | ||||||||||