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pH regulation in anoxic rice coleoptiles at pH 3.5: biochemical pHstats and net H+ influx in the absence and presence of NOFormula.

Greenway H, Kulichikhin KY, Cawthray GR, Colmer TD - J. Exp. Bot. (2011)

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: The University of Western Australia, Crawley, WA, Australia.

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.

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Schematic presentation of the O2 regime, pH treatment, and composition of the medium. (This figure is available in colour at JXB online.)
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fig1: Schematic presentation of the O2 regime, pH treatment, and composition of the medium. (This figure is available in colour at JXB online.)

Mentions: For excised coleoptile tips, the time schedule, including the various treatments, is shown in Fig. 1. Raising seedlings and pre-treatment of excised tips have been described in previous papers (Huang et al., 2005; Kulichikhin et al., 2009). Briefly, after 48 h aeration followed by an 18 h hypoxic pre-treatment at 0.05 mM O2, 7–10 mm tips were excised from coleoptiles and 0.1–0.13 g fresh weight was each placed in a 50 ml conical flask. After 5 h healing at 0.05 mM O2, anoxia was imposed. The substrate supply of the seed was replaced by exogenous glucose. Glucose was at 20 mM after excision and was increased to 50 mM during anoxia, because at 20 mM glucose endogenous sugar levels still decrease over several days of anoxia (Huang et al., 2005). All stages were in darkness.


pH regulation in anoxic rice coleoptiles at pH 3.5: biochemical pHstats and net H+ influx in the absence and presence of NOFormula.

Greenway H, Kulichikhin KY, Cawthray GR, Colmer TD - J. Exp. Bot. (2011)

Schematic presentation of the O2 regime, pH treatment, and composition of the medium. (This figure is available in colour at JXB online.)
© Copyright Policy - creative-commons
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC3295390&req=5

fig1: Schematic presentation of the O2 regime, pH treatment, and composition of the medium. (This figure is available in colour at JXB online.)
Mentions: For excised coleoptile tips, the time schedule, including the various treatments, is shown in Fig. 1. Raising seedlings and pre-treatment of excised tips have been described in previous papers (Huang et al., 2005; Kulichikhin et al., 2009). Briefly, after 48 h aeration followed by an 18 h hypoxic pre-treatment at 0.05 mM O2, 7–10 mm tips were excised from coleoptiles and 0.1–0.13 g fresh weight was each placed in a 50 ml conical flask. After 5 h healing at 0.05 mM O2, anoxia was imposed. The substrate supply of the seed was replaced by exogenous glucose. Glucose was at 20 mM after excision and was increased to 50 mM during anoxia, because at 20 mM glucose endogenous sugar levels still decrease over several days of anoxia (Huang et al., 2005). All stages were in darkness.

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: The University of Western Australia, Crawley, WA, Australia.

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.

Show MeSH
Related in: MedlinePlus