The MIFETM system 
for non-invasive measurement of specific fluxes in solution near living plant or animal tissue

 
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Osmoregulation

Other MIFE applications: in Plant physiology, they include stress; adaptation; mineral nutrition; photosynthesis; long-distance transport; growth & development; water relations; osmoregulation; hormonal physiology; stomatal physiology; plant movements.

 

Hyperosmotic stress is known to significantly enhance net uptake of inorganic ions into plant cells. Until recent, direct evidence for cell turgor recovery via such a mechanism was still lacking. By combining MIFE ion flux measurements with measuring cell turgor changes (with the pressure-probe technique), direct evidence that inorganic ion uptake regulates turgor in osmotically-stressed Arabidopsis thaliana epidermal root cells were obtained (Shabala and Lew 2002). Immediately after onset of hyperosmotic stress the cell turgor dropped from 0.65 MPa to about 0.25 MPa. Turgor recovery started within 2 to 10 min after the treatment and was accompanied by a significant (30 to 80 nmol m-2 s-1) increase in uptake of K+, Cl- and Na+ by root cells. In most cells, almost complete (>90% of initial values) recovery of the cell turgor was observed within 40 to 50 min after stress onset. Similar results were obtained for other plant tissues (Shabala et al 2000; Chen et al 2007), as well as bacterial (Shabala et al. 2009) and fungal (Lew et al 2006) systems. 

Turgor, V, Flux ProbesMicrophotgraphic examples of pressure probe (A) and ion-flux/voltage-clamp measurements (B). The micropipette tip is indicated by an arrow in A. It is located in the vacuole. In B, the double-barrelled microelectrode is impaled into the cytoplasm. The ion fluxes from the root hair were measured parallel to the root surface. Bar = 20mm.


Turgor  Model

A model illustrating pathways of fast turgor adjustment in Arabidopsis root cells. Hyperosmotic shock, sensed via an osmosensor activates the H+-ATPase. The hyperpolarization increases net K+ uptake thorough an inward K+ channel and concomitantly decreases K+ efflux through an outward K_ channel. Both the hyperpolarized potential and extracellular acidification increase uptake of Cl- through a H+ /Cl- symporter.





Turgor Recovery

A typical recording of the turgor recovery in Arabidopsis epidermal root cell upon onset of hyperosmotic  stress.

AminoAcids Treatment TableThe MIFE technique was also successfully used to re-evaluate the role of compatible solutes in plant adaptive responses to salinity and osmotic stress. We have explicitly demonstrated that the function of compatible solutes is not limited by conventional osmoprotection and showed that inorganic osmolytes (sugars, amino acids, polyoles and quaternary amines) play an important role in regulation of ion transport across cellular membranes, adjusting metabolic pathways to altered environmental conditions, scavenging ROS, maintaining optimal cytosolic K+ homeostasis and adjusting cell turgor by preventing NaCl-induced K+ leakage from the cell, mainly via depolarisation-activated outward-rectifying (GORK) K+ channels (Cuin and Shabala 2007, 2008; Shabala and Cuin 2008).  Overall, our results provide the first direct evidence for regulation of ion fluxes across the plasma membrane by physiologically relevant low concentrations of compatible solutes and for the critical role of intracellular K+ homeostasis in plant salt tolerance. Specific signal transduction pathways have been investigated, revealing the critical role of voltage gating in this process. These findings have opened a new and exciting avenue for genetic improvement of plant salt tolerance by targeting transport systems and signal transduction pathways responsible for maintaining optimal K+ levels in cell cytosol. 

For more details and reprints, see #9, #12, #13, #14, #28, #39, #55  {{ Needs updatiing }}

K fluxes with AminoAcids

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Maintained by Ian Newman. Date . University of Tasmania.