Active ion uptake

R. J. Haynes, Active ion uptake and maintenance of cation-anion balance a critical examination of their role in regulating rhizosphere pH. Plant Soil 726 247 (1990). 

Fig. 229. Theory of active ion uptake according to Lundegardh (modified from Finck 1969).

That all sounds very impressive. However, the fact should not be hidden that there are other hypotheses regarding the uptake of ions by the root. Most of the facts, though, do argue in favor of the fundamental validity of the theory of active ion uptake. 

The hypothesis that active ion uptake operates through carrier systems requires us to consider how the operation of such systems could depend upon energy released by metabolism. Referring to Fig. 7.3, we see that energy could be used for regeneration of the... 

The reference above to the inhibition of salt absorption by chloramphenicol, an inhibitor of protein synthesis, can now serve to introduce one of the most interesting recent hypotheses. This arose from the observations that when the dormant cells of storage organs (potatoes, beets) are activated by washing in aerated distilled water then they develop not only a capacity for primary salt absorption but also for protein synthesis, and certain factors seem to affect these two processes in the same way. However, the concept that there was a close functional relationship between these two processes seemed to face the difficulty that active ion uptake can take place into cells in which there is no net protein synthesis. However, studies involving the use of the mass isotope of nitrogen (N ) have shown that in... 

We recently synthesized several reasonably surface-active crown-ether-based ionophores. This type of ionophore in fact gave Nernstian slopes for corresponding primary ions with its ionophore of one order or less concentrations than the lowest allowable concentrations for Nernstian slopes with conventional counterpart ionophores. Furthermore, the detection limit was relatively improved with increased offset potentials due to the efficient and increased primary ion uptake into the vicinity of the membrane interface by surfactant ionophores selectively located there. These results were again well explained by the derived model essentially based on the Gouy-Chapman theory. Just like other interfacial phenomena, the surface and bulk phase of the ionophore incorporated liquid membrane may naturally be speculated to be more or less different. The SHG results presented here is one of strong evidence indicating that this is in fact true rather than speculation. 

Less complex techniques have been reported to be useful to study the acidic and alkaline treatment processes of biosorbents and the role of carboxyl and carboxylate groups in metal adsorption. Rakhshaee and coworkers101 used potentiometric titration curves to assess the content of such groups in L. minor biomass treated with NaOH and HC1. The results showed an increase (up to 25%) in the adsorption of Hg(II), Cr(III), Cr(VI), and Cu(II) with NaOH-treated biomass as a consequence of an increase of -COO- groups (0.92-2.42 mmol/g). On the contrary, the -COOH groups increase observed (1.50-2.41 mmol/g) due to the acidic treatment led to a decrease in the metal ions uptake (up to 33%) despite activation by the chloride salts. 

Several different changes in mitochondria occur during apoptosis. These include a change in membrane potential (usually depolarization), increased production of reactive oxygen species, potassium channel activation, calcium ion uptake, increased membrane permeability and release of cytochrome c and apoptosis inducing factor (AIF) [25]. Increased permeability of the mitochondrial membranes is a pivotal event in apoptosis and appears to result from the formation of pores in the membrane the proteins that form such permeability transition pores (PTP) may include a voltage-dependent anion channel (VDAC), the adenine nucleotide translocator, cyclophilin D, the peripheral benzodiazepine receptor, hexokinase and... 

A sarcoplasmic reticulum protein, known as phospho-lambam, phosphorylation of which increases the activity of the Ca ion uptake process in the reticulum and hence the concentration of Ca ions in the cytoplasm decreases more rapidly. This results in a decrease in the relaxation time of the muscle and hence an increase in heart rate. 

Maggioni, A., Varanini, Z., Nardi, S., and Pinton, R. (1987). Action of soil humic matter on plant roots stimulation of ion uptake and effects on (Mg2+ + K+) ATPase activity. Sci. Total Environ. 62, 355-363. 

Modes of action of allelochemicals are diverse and have been described for isolated compounds, as well as for mixtures. They can affect various physiological processes, such as disruption of membrane permeability,22 ion uptake,28 inhibition of electron transport in photosynthesis and respiratory chain,1,10,33 alterations of some enzymatic activities, 1 and inhibition of cell division, 1 among others. 

Copper ion homeostasis in prokaryotes involves Cu ion efflux and sequestration. The proteins involved in these processes are regulated in their biosynthesis by the cellular Cu ion status. The best studied bacterial Cu metalloregulation system is found in the gram-positive bacterium Enterococcus hirae. Cellular Cu levels in this bacterium control the expression of two P-type ATPases critical for Cu homeostasis (Odermatt and Solioz, 1995). The CopA ATPase functions in Cu ion uptake, whereas the CopB ATPase is a Cu(I) efflux pump (Solioz and Odermatt, 1995). The biosynthesis of both ATPases is regulated by a Cu-responsive transcription factor, CopY (Harrison et al., 2000). In low ambient Cu levels Cop Y represses transcription of the two ATPase genes. On exposure to Cu(I), CopY dissociates from promoter/operator sites on DNA with a for Cu of 20 jlM (Strausak and Solioz, 1997). Transcription of copA and copB proceeds after dissociation of CuCopY. The only other metal ions that induce CopY dissociation from DNA in vitro are Ag(I) and Cd(II), although the in vivo activation of copA and copB is specihc to Cu salts. The CuCopY complex is dimeric with two Cu(I) ions binding per monomer (C. T. Dameron, personal communication). The structural basis for the Cu-induced dissociation of CopY is unknown. Curiously, CopY is also activated in Cu-dehcient cells, but the mechanism is distinct from the described Cu-induced dissociation from DNA (Wunderh-Ye and Solioz, 1999). 

Fig. 3. Mad activates the expression of three gene products involved in high-affinity copper ion uptake in Saccharomyces cerevisiae. Two genes encode Cu ion permeases Ctrl and Ctr3. The third is one of two metalloreductases that reduce Cu(II) ions prior to uptake. Mad is a transcriptional activator in Cu-deficient yeast cells.

As the Q10 indicates, the passive uptake of this ion doubles with only a 10°C increase in temperature. Therefore, a passive process can have a rather high Q10 if there is a substantial energy barrier, so such a Q10 for ion uptake does not necessarily indicate active transport. 

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