title: Mechanism of rapid suppression of cell expansion in cucumber hypocotyls after blue-light irradiation.
abstract: Rapid suppression of hypocotyl elongation by blue light in cucumber (Cucumis sativus L.) was studied to examine possible hydraulic and wall changes responsible for diminished growth.  Cell-sap osmotic pressure, measured by vapor-pressure osmometry, was not decreased by blue light; turgor pressure, measured by the pressure-probe technique, remained constant during the growth inhibition; and stem hydraulic conductance, measured by dynamic and static methods, was likewise unaffected by blue light.  Wall yielding properties were assessed by the pressure-block technique for in-vivo stress relaxation.  Blue light reduced the initial rate of relaxation by 77%, but had little effect on the final amount of relaxation.  The results demonstrate that blue irradiation acts to decrease the wall yielding coefficient, but not the yield threshold.  Stress-strain (Instron) analysis showed that irradiation of the seedlings had little effect on the mechanical extensibilities of the isolated wall.  The results indicate that blue light can reduce cell-wall loosening without affecting bulk viscoelastic properties, and indicate a chemorheological mechanism of cell-wall expansion.
authors.affiliation: Department of Biology, Pennsylvania State University, University Park 16802, USA.
authors.forename: D J
authors.initials: DJ
authors.lastname: Cosgrove
mesh_terms: D055592:Biophysical Phenomena; D001703:Biophysics; D002473:Cell Wall / Q000502:physiology; D018553:Cucumis sativus / Q000166:cytology* / Q000254:growth & development* / Q000502:physiology / Q000528:radiation effects; D018546:Hypocotyl / Q000166:cytology* / Q000254:growth & development* / Q000502:physiology / Q000528:radiation effects; D008027:Light; D008954:Models, Biological; D009995:Osmosis; D010812:Physical Stimulation; D018547:Plant Stems / Q000502:physiology; D013997:Time Factors