title: Low air humidity increases leaf-specific hydraulic conductance of Arabidopsis thaliana (L.) Heynh (Brassicaceae).
abstract: The typical isohydric plant response to low relative humidity involves stomatal closure, followed by long-term responses like adjustment of shoot-to-root ratios. Little information is available on the early responses of the root system to exposure of shoots to low humidity, nor is it clear to what extent responses of Arabidopsis thaliana conform to the isohydric model. In this study, A. thaliana plants grown hydroponically at high humidity were exposed to two constant relative humidities, 17% and 77%, while the root system remained in aerated nutrient solution. Leaf conductance (g(s)), transpiration, water potential (Psi(l)), osmotic potential, and whole plant hydraulic conductance (K) were determined for the following time intervals: 0-10, 10-20, and 20-40 min, and 0-5, 5-10, and 24-29 h. At low relative humidity, no change in g(s) was detected. Psi(l) decreased by 0.28 MPa during the first 5 h and then remained stable. During the first hour, leaf-specific K averaged 1.6 x 10(-5) kg MPa(-1) m(-2) s(-1) at high humidity. At low humidity it increased >3-fold to 5.8 x 10(-5) kg MPa(-1) m(-2) s(-1). Similar significant differences in K were observed during all time periods. Low concentration mercury amendments in the hydroponic solution (5 microM and 10 microM HgCl(2)) had no discernible influence, but pre-exposure to 50 microM HgCl(2) reduced K differences between humidity treatments. As HgCl(2) is known to be a potent inhibitor of aquaporin function, this suggests that aquaporins may have played a role in the fast hydraulic response of plants transferred to low humidity. The rapid hydraulic response and the influence of mercury raise the possibility that an alternative response to atmospheric dryness is increased K modulated by aquaporins.
authors.affiliation: Institute of Field and Garden Crops, The Volcani Center, Bet Dagan 50250, Israel.
authors.forename: Michal
authors.initials: M
authors.lastname: Levin
authors.forename: Jorge Hugo
authors.initials: JH
authors.lastname: Lemcoff
authors.forename: Shabtai
authors.initials: S
authors.lastname: Cohen
authors.forename: Yoram
authors.initials: Y
authors.lastname: Kapulnik
mesh_terms: D020346:Aquaporins / Q000378:metabolism; D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D006813:Humidity; D008627:Mercuric Chloride / Q000494:pharmacology; D018515:Plant Leaves / Q000187:drug effects / Q000378:metabolism*; D018520:Plant Shoots / Q000378:metabolism; D018526:Plant Transpiration / Q000187:drug effects / Q000502:physiology*; D013997:Time Factors; D014867:Water / Q000378:metabolism
chemical_list: D020346:Aquaporins; D014867:Water; D008627:Mercuric Chloride