JXB Advance Access originally published online on April 10, 2009
Journal of Experimental Botany 2009 60(7):2119-2128; doi:10.1093/jxb/erp090
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© 2009 The Author(s).
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
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RESEARCH PAPER |
Regulation of intracellular pH during anoxia in rice coleoptiles in acidic and near neutral conditions
1School of Plant Biology, Faculty of Natural and Agricultural Sciences, The University of Western Australia, 35 Stirling Highway, Crawley, 6009, WA, Australia
2School of Biomedical, Biomolecular and Chemical Sciences, Faculty of Life and Physical Sciences, The University of Western Australia, 35 Stirling Highway, Crawley, 6009, WA, Australia
3Laboratory of Photosynthesis, Biological Scientific Research Institute of Saint-Petersburg State University, Oranienbaumskoe shosse 2, Stary Peterhof, Saint-Petersburg 198504, Russia
To whom correspondence should be addressed. E-mail: tdcolmer{at}cyllene.uwa.edu.au
Rice coleoptiles, renowned for anoxia tolerance, were hypoxically pretreated, excised, ‘healed’, and then exposed to a combination of anoxia and pH 3.5. The putative acid load was confirmed by net effluxes of K+ to the medium, with concurrent net decreases of H+ in the medium, presumably mainly due to H+ influx. Yet the coleoptiles survived the combination of anoxia and pH 3.5 for at least 90 h, and even for at least 40 h when the energy crisis, inherent to anoxia, had been aggravated by supplying the coleoptiles with 2.5 mM rather than 50 mM glucose. Even in the case of coleoptiles with 2.5 mM glucose, an accumulation ratio of 6 for Cl– was attained at 4 h after the start of re-aeration, implying plasma membrane integrity was either maintained during anoxia, or rapidly restored after a return to aerated conditions. Cytoplasmic pH and vacuolar pH were measured using in vivo 31P nuclear magnetic resonance spectroscopy with 50 mM glucose in the basal perfusion medium. After 60 h in anoxia, external pH was suddenly decreased from 6.5 to 3.5, but cytoplasmic pH only decreased from 7.35 to 7.2 during the first 2 h and then remained steady for the next 16 h. During the first 3 h at pH 3.5, vacuolar pH decreased from 5.7 to 5.25 and then stabilized. After 18 h at pH 3.5, the initial values of cytoplasmic pH and vacuolar pH were rapidly restored, both upon a return to pH 6.5 while maintaining anoxia and after subsequent return to aerated solution. Summing up, rice coleoptiles exposed to a combination of anoxia and pH 3.5 retained pH regulation and cellular compartmentation, demonstrating tolerance to anoxia even during the acid load imposed by exposure to pH 3.5.
Key words: Acid load, anoxia, cytoplasmic pH, energy requirements, in vivo NMR, Oryza sativa, pH regulation, proton fluxes, rice coleoptiles, vacuolar pH
* Present address: Department of Plant Science, University of Manitoba, 222 Agriculture Building, 66 Dafoe Road, Winnipeg, Manitoba, Canada R3T 2N2.
Definitions: Acid load, environments that tend to decrease cellular pH. Such loads can be imposed by exposure of a tissue to a weak acid, or to low external pH; accumulation ratio, internal/external concentration; energy crisis, when the energy supply to cells is severely restricted, as will be the case during anoxia. The term ‘crisis’ is chosen since, for the cells to survive, the scarce energy supply needs to be economized and prioritized (term suggested by BJ Atwell; see also Greenway and Gibbs, 2003).
Received 21 December 2008; Revised 28 February 2009 Accepted 2 March 2009