title: Transport properties of the mung bean (Vigna radiata) non-aerial hypocotyl membrane: permselectivity to hydrophilic compounds.
abstract: BACKGROUND
  Aerial plant surfaces are covered by a lipophilic cuticular membrane (CM) that restricts the transport of water and small solutes. Non-aerial tissues do not exhibit such a barrier. Recent data have shown that large relative to CM hydrophilic agrochemicals were able to pass at high rates through the non-aerial coleoptile.
  
  
  RESULTS
  A moderately large hydrophilic solute like PEG 1000 with a mean molar volume of 782 cm(3) mol(-1) was rejected by the non-aerial hypocotyl. Uptake of smaller solutes like urea (46.5 cm(3) mol(-1) ) was fast and with 99% after 1 day. Cut-off size estimations suggest a pore size diameter below 1.5 nm.
  
  
  CONCLUSIONS
  Aerial and non-aerial CM differ largely in their absolute barrier properties. This difference is related to the absence of embedded cuticular waxes in the non-aerial hypocotyl membrane, which make the CM physically dense and cause low solubility of hydrophilic solutes. The free volume for diffusion at the interface of the non-aerial hypocotyl cuticle to the environment is much larger resulting in higher penetration rates. It is suggested that diffusion through the non-aerial hypocotyl does not proceed in a real channel system with continuous aqueous phase but is more like transport through a filter with restricted diffusion in the pore openings.
authors.affiliation: Faculty of Natural Sciences, Leibniz University of Hannover, Hannover, Germany.
authors.forename: John
authors.initials: J
authors.lastname: Aponte
authors.forename: Peter
authors.initials: P
authors.lastname: Baur
mesh_terms: D001692:Biological Transport; D004058:Diffusion; D007887:Fabaceae / Q000378:metabolism*; D057927:Hydrophobic and Hydrophilic Interactions; D018546:Hypocotyl / Q000378:metabolism*; D011092:Polyethylene Glycols / Q000737:chemistry / Q000378:metabolism*; D012995:Solubility
chemical_list: D011092:Polyethylene Glycols
keywords: hydrophilic agrochemicals; hypocotyl; penetration; permselective; pores; radius