Onion root water transport sensitive to water channel and K+ channel inhibitors.
Transroot osmotic water flux (Jos) and radial hydraulic conductivity (Lpr) in onion roots were greatly increased by three means; infiltration of roots by pressurization, repetition of osmosis and chilling at 5 degrees C. Jos was strongly reduced by the water channel inhibitor HgCl2 (91%) and the K+ channel inhibitor nonyltriethylammonium (C9, 75%), which actually made the membrane potential of root cells less sensitive to K+. C9 decreased the rate of turgor reduction induced by sorbitol solution to the same extent as HgCl2. Thus, C9 is assumed to decrease the hydraulic conductivity (Lp) of the plasma membrane by blocking water channels, although possible inhibition of the plasmodesmata of the root symplast by C9 cannot be excluded. Onion roots transported water from the tip to the base in the absence of the osmotic gradient. This non-osmotic water flux (Jnos) was equivalent to Jos induced by 0.029 M sorbitol. Jnos increased when Jos was increased by repetition of osmosis and decreased when Jos was decreased by either HgCl2 or by C9. The correlation between Jnos and Jos suggests that non-osmotic water transport occurs via the same pathways as those for osmotic water transport.
Tazawa
M
M
Department of Applied Physics and Chemistry, Fukui University of Technology, Gakuen, Fukui, 910-8505, Japan. Masashi.Tazawa@mb5.seikyou.ne.jp
Sutou
E
E
Shibasaka
M
M
D020346:Aquaporins / Q000037:antagonists & inhibitors*; D001692:Biological Transport / Q000187:drug effects; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008627:Mercuric Chloride / Q000494:pharmacology*; D019697:Onions / Q000378:metabolism*; D009995:Osmosis / Q000187:drug effects / Q000502:physiology; D009997:Osmotic Pressure / Q000187:drug effects; D018517:Plant Roots / Q000378:metabolism; D026902:Potassium Channel Blockers; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology; D013012:Sorbitol / Q000494:pharmacology
D020346:Aquaporins; D026902:Potassium Channel Blockers; D000644:Quaternary Ammonium Compounds; C033910:nonyltriethylammonium; D013012:Sorbitol; D008627:Mercuric Chloride