title: Nitrate signalling to stomata and growing leaves: interactions with soil drying, ABA, and xylem sap pH in maize.
abstract: Increasing the nitrate (N) concentration in the rooting substrate above deficiency decreased stomatal conductance and leaf growth rate compared with sufficient N in maize seedlings (Zea mays L.) growing in drying substrate. Novel effects were detected when N in the non-deficient range was supplied directly to the xylem of detached shoots: concentrations above 2.0 mol m-3 KNO3 reduced transpiration, and concentrations above 12 mol m-3 KNO3 reduced leaf growth rate. Evidence is provided that the novel effects of N on transpiration and growth were mediated by pH-based ABA redistribution. ABA at 0.05 mol m-3, whilst ineffective alone, sensitized leaf growth to increases in KNO3 concentration (from 3.0 mol m-3), and the capacity of higher concentrations of ABA to reduce growth was enhanced by KNO3. Transpiration was sensitively reduced by KNO3, ABA, or buffers adjusted to pH 6.7-7.0 (compared with buffers adjusted to pH 5.0) alone. Nevertheless, a synergistic effect of KNO3 and either ABA or buffers adjusted to pH 6.7-7.0 was observed. Buffers of pH 5.6 supplied to detached shoots alleviated the depression of transpiration caused by 12 mol m-3 KNO3. Buffers adjusted to pH 6.7 increased the sensitivity of growth to KNO3. Xylem sap extracted from intact seedlings growing in drying soil exhibited an initial increase in N concentration, followed by a decrease at progressively lower soil water potentials. The importance for novel N signalling above deficiency is discussed with reference to the generality of fluctuations in soil and xylem N concentration within this range.
authors: The Lancaster Environment Centre, Lancaster University, Bailrigg, Lancaster LA1 4YQ, UK. sally.wilkinson@lancaster.ac.uk
authors: Sally
authors: S
authors: Wilkinson
authors: Mark A
authors: MA
authors: Bacon
authors: William J
authors: WJ
authors: Davies
mesh_terms: D000040:Abscisic Acid / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D009566:Nitrates / Q000378:metabolism* / Q000494:pharmacology; D018515:Plant Leaves / Q000378:metabolism; D018520:Plant Shoots / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism; D018526:Plant Transpiration; D017680:Potassium Compounds / Q000494:pharmacology; D015398:Signal Transduction; D012987:Soil; D014867:Water / Q000378:metabolism*; D052584:Xylem / Q000737:chemistry / Q000378:metabolism; D003313:Zea mays / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism*
chemical_list: D009566:Nitrates; D017680:Potassium Compounds; D012987:Soil; D014867:Water; D000040:Abscisic Acid; C023844:potassium nitrate