title: The stomatal response to reduced relative humidity requires guard cell-autonomous ABA synthesis.
abstract: Stomata are pores on the leaf surface, bounded by two guard cells, which control the uptake of CO(2) for photosynthesis and the concomitant loss of water vapor. In 1898, Francis Darwin showed that stomata close in response to reduced atmospheric relative humidity (rh); however, our understanding of the signaling pathway responsible for coupling changes in rh to alterations in stomatal aperture is fragmentary. The results presented here highlight the primacy of abscisic acid (ABA) in the stomatal response to drying air. We show that guard cells possess the entire ABA biosynthesis pathway and that it appears upregulated by positive feedback by ABA. When wild-type Arabidopsis and the ABA-deficient mutant aba3-1 were exposed to reductions in rh, the aba3-1 mutant wilted, whereas the wild-type did not. However, when aba3-1 plants, in which ABA synthesis had been specifically rescued in guard cells, were challenged with dry air, they did not wilt. These data indicate that guard cell-autonomous ABA synthesis is required for and is sufficient for stomatal closure in response to low rh. Guard cell-autonomous ABA synthesis allows the plant to tailor leaf gas exchange exquisitely to suit the prevailing environmental conditions.
authors.affiliation: Institute for Molecular Plant Physiology and Biophysics, Biocenter, University of Wuerzburg, 97082 Wuerzburg, Germany.
authors.forename: Hubert
authors.initials: H
authors.lastname: Bauer
authors.forename: Peter
authors.initials: P
authors.lastname: Ache
authors.forename: Silke
authors.initials: S
authors.lastname: Lautner
authors.forename: Joerg
authors.initials: J
authors.lastname: Fromm
authors.forename: Wolfram
authors.initials: W
authors.lastname: Hartung
authors.forename: Khaled A S
authors.initials: KA
authors.lastname: Al-Rasheid
authors.forename: Sophia
authors.initials: S
authors.lastname: Sonnewald
authors.forename: Uwe
authors.initials: U
authors.lastname: Sonnewald
authors.forename: Susanne
authors.initials: S
authors.lastname: Kneitz
authors.forename: Nicole
authors.initials: N
authors.lastname: Lachmann
authors.forename: Ralf R
authors.initials: RR
authors.lastname: Mendel
authors.forename: Florian
authors.initials: F
authors.lastname: Bittner
authors.forename: Alistair M
authors.initials: AM
authors.lastname: Hetherington
authors.forename: Rainer
authors.initials: R
authors.lastname: Hedrich
mesh_terms: D000040:Abscisic Acid / Q000096:biosynthesis*; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D002245:Carbon Dioxide / Q000378:metabolism; D025461:Feedback, Physiological; D006813:Humidity; D010788:Photosynthesis; D054046:Plant Stomata / Q000502:physiology*; D059467:Transcriptome
chemical_list: D002245:Carbon Dioxide; D000040:Abscisic Acid