title: Do increases in xylem sap pH and/or ABA concentration mediate stomatal closure following nitrate deprivation?
abstract: Stomatal conductance (g(s)) of pepper (Capsicum annuum L.) plants decreased during the second photoperiod (day 2) after withholding nitrate (N). Stomatal closure of N-deprived plants was not associated with a decreased shoot water potential (Psi(shoot)); conversely Psi(shoot) was lower in N-supplied plants. N deprivation transiently (days 2 and 3) alkalized (0.2-0.3 pH units) xylem sap exuded from de-topped root systems under root pressure, and xylem sap expressed from excised shoots by pressurization. The ABA concentration of expressed sap increased 3-4-fold when measured on days 2 and 4. On day 2, leaves detached from N-deprived and N-supplied plants showed decreased transpiration rates when fed an alkaline (pH 7) artificial xylem (AX) solution, independent of the ABA concentration (10-100 nM) supplied. Thus changes in xylem sap composition following N deprivation can potentially close stomata. However, the lower transpiration rate of detached N-deprived leaves relative to N-supplied leaves shows that factors residing within N-deprived leaves also mediate stomatal closure, and that these factors assume greater importance as the duration of N deprivation increases.
authors.affiliation: Department of Botany, The University of Queensland, Brisbane, QLD 4072, Australia. I.Dodd@lancaster.ac.uk
authors.forename: I C
authors.initials: IC
authors.lastname: Dodd
authors.forename: L P
authors.initials: LP
authors.lastname: Tan
authors.forename: J
authors.initials: J
authors.lastname: He
mesh_terms: D000040:Abscisic Acid / Q000494:pharmacology*; D002212:Capsicum / Q000737:chemistry / Q000187:drug effects / Q000502:physiology*; D006863:Hydrogen-Ion Concentration; D009566:Nitrates / Q000494:pharmacology*; D009584:Nitrogen / Q000378:metabolism; D018515:Plant Leaves / Q000737:chemistry / Q000187:drug effects / Q000502:physiology*; D018526:Plant Transpiration / Q000187:drug effects / Q000502:physiology*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D014867:Water / Q000502:physiology
chemical_list: D009566:Nitrates; D014867:Water; D000040:Abscisic Acid; D009584:Nitrogen