title: Super-elevated CO2 interferes with stomatal response to ABA and night closure in soybean (Glycine max).
abstract: Studies have shown stomatal conductance (g(s)) of plants exposed to super-elevated CO2 (>5000micromol mol(-1)) increases in several species, in contrast to a decrease of g(s) caused by moderate CO2 enrichment. We conducted a series of experiments to determine whether super-elevated CO2 alters stomatal development and/or interferes with stomatal closure in soybean (Glycine max). Plants were grown at nominal ambient (400), elevated (1200) and super-elevated (10,000micromol mol(-1)) CO2 in controlled environmental chambers. Stomatal density of the plant leaf was examined by a scanning electron microscope (SEM), while the stomatal response to the application of exogenous abscisic acid (ABA), a phytohormone associated with water stress and stomatal control, was investigated in intact growing plants by measuring the g(s) of abaxial leaf surfaces using a steady-state porometer. Relative to the control (400micromol mol(-1) CO2) plants, daytime stomatal conductance (g(s,day)) of the plants grown under 1200 and 10,000micromol mol(-1) CO2 was reduced by 38% and 15%, respectively. Dark period stomatal conductance (g(s,night)) was unaffected by growing under 1200mumol mol(-1) CO2) but dramatically increased under 10,000micromol mol(-1) CO2. Stomatal density increased by 10% in the leaves of 10,000micromol mol(-1) CO2-grown plants, which in part contributed to the higher g(s,night) values. Elevating [CO2] to 1200micromol mol(-1) enhanced ABA-induced stomatal closure, but further increasing CO2 to 10,000micromol mol(-1) significantly reduced ABA-induced stomatal closure. These results demonstrated that stomatal response to ABA is CO2 dependent. Hence, a stomatal failure to effectively respond to an ABA signal and to close at night under extremely high CO2 may increase plants susceptibility to other abiotic stresses.
authors.affiliation: Dynamac Corp., Space Life Sciences Laboratory, Kennedy Space Center, FL 32899, USA. lanfang.h.levine@nasa.gov
authors.forename: Lanfang H
authors.initials: LH
authors.lastname: Levine
authors.forename: Jeffrey T
authors.initials: JT
authors.lastname: Richards
authors.forename: Raymond M
authors.initials: RM
authors.lastname: Wheeler
mesh_terms: D000040:Abscisic Acid / Q000494:pharmacology*; D002245:Carbon Dioxide / Q000494:pharmacology*; D018506:Gene Expression Regulation, Plant / Q000187:drug effects / Q000502:physiology; D018515:Plant Leaves / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D054046:Plant Stomata / Q000187:drug effects* / Q000502:physiology; D018526:Plant Transpiration / Q000187:drug effects / Q000502:physiology; D013025:Glycine max / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology*
chemical_list: D002245:Carbon Dioxide; D000040:Abscisic Acid