title: pH regulation in anoxic rice coleoptiles at pH 3.5: biochemical pHstats and net H+ influx in the absence and presence of NOFormula.
abstract: During anoxia, cytoplasmic pH regulation is crucial. Mechanisms of pH regulation were studied in the coleoptile of rice exposed to anoxia and pH 3.5, resulting in H(+) influx. Germinating rice seedlings survived a combination of anoxia and exposure to pH 3.5 for at least 4 d, although development was retarded and net K(+) efflux was continuous. Further experiments used excised coleoptile tips (7-10 mm) in anoxia at pH 6.5 or 3.5, either without or with 0.2 mM NO(3)(-), which distinguished two processes involved in pH regulation. Net H(+) influx (μmol g(-1) fresh weight h(-1)) for coleoptiles with NO(3)(-) was ∼1.55 over the first 24 h, being about twice that in the absence of NO(3)(-), but then decreased to 0.5-0.9 as net NO(3)(-) uptake declined from ∼1.3 to 0.5, indicating reduced uptake via H(+)-NO(3)(-) symports. NO(3)(-) reduction presumably functioned as a biochemical pHstat. A second biochemical pHstat consisted of malate and succinate, and their concentrations decreased substantially with time after exposure to pH 3.5. In anoxic coleoptiles, K(+) balancing the organic anions was effluxed to the medium as organic anions declined, and this efflux rate was independent of NO(3)(-) supply. Thus, biochemical pHstats and reduced net H(+) influx across the plasma membrane are important features contributing to pH regulation in anoxia-tolerant rice coleoptiles at pH 3.5.
authors.affiliation: The University of Western Australia, Crawley, WA, Australia.
authors.forename: Hank
authors.initials: H
authors.lastname: Greenway
authors.forename: Konstantin Y
authors.initials: KY
authors.lastname: Kulichikhin
authors.forename: Gregory R
authors.initials: GR
authors.lastname: Cawthray
authors.forename: Timothy D
authors.initials: TD
authors.lastname: Colmer
mesh_terms: D000222:Adaptation, Physiological; D001692:Biological Transport; D002264:Carboxylic Acids / Q000032:analysis / Q000378:metabolism; D015687:Cell Hypoxia; D002463:Cell Membrane Permeability; D018548:Cotyledon / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism / Q000502:physiology*; D000431:Ethanol / Q000378:metabolism; D018525:Germination; D006863:Hydrogen-Ion Concentration; D008293:Malates / Q000032:analysis / Q000378:metabolism; D009566:Nitrates / Q000494:pharmacology*; D012275:Oryza / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism / Q000502:physiology*; D010100:Oxygen / Q000494:pharmacology; D036226:Seedlings / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism / Q000502:physiology; D013312:Stress, Physiological / Q000502:physiology*; D019802:Succinic Acid / Q000032:analysis / Q000378:metabolism
chemical_list: D002264:Carboxylic Acids; D008293:Malates; D009566:Nitrates; D000431:Ethanol; C030298:malic acid; D019802:Succinic Acid; D010100:Oxygen