title: Salt stress upregulates periplasmic arabinogalactan proteins: using salt stress to analyse AGP function.
abstract: Arabinogalactan proteins (AGPs) are implicated in cell expansion by unknown mechanisms, thus AGP content and cell-expansion rate might be correlated. We used Yariv reagent to quantify release rates and distribution of AGP at the cell surface of tobacco BY-2 cells: plasma membrane (M); soluble periplasmic AGPs released by cell rupture (S); cell wall (W); and growth medium (Gsink). In contrast to earlier reports, we observed massive upregulation of AGPs in salt-stressed cells, and hence the absence of a simple, direct cause-and-effect relationship between growth rate and AGP release. There was a more subtle connection. A dynamic flux model, M-->S-->W-->Gsink, indicated that turnover was nondegradative, with little free diffusion of AGPs trapped in the pectic matrix of nonadapted cells where transmural migration of high molecular-weight AGPs occurred mainly by plug flow (apposition and extrusion). In contrast, however, an up to sixfold increased AGP release rate in the slower-growing salt-adapted cells indicated a greatly increased rate of AGP diffusion through a much more highly porous pectic network. We hypothesize that classical AGPs act as pectin plasticizers. This explains how beta-D-glycosyl Yariv reagents might inhibit expansion growth by crosslinking monomeric AGPs, and thus mimic an AGP loss-of-function mutation.
authors.affiliation: School of Life Sciences, John Maynard Smith Building, University of Sussex, Falmer, Brighton BN1 9QG, UK. d.t.a.Lamport@sussex.ac.uk
authors.forename: Derek T A
authors.initials: DT
authors.lastname: Lamport
authors.forename: Marcia J
authors.initials: MJ
authors.lastname: Kieliszewski
authors.forename: Allan M
authors.initials: AM
authors.lastname: Showalter
mesh_terms: D000064:Acclimatization; D049108:Cell Enlargement; D002462:Cell Membrane / Q000378:metabolism; D002473:Cell Wall / Q000378:metabolism; D002478:Cells, Cultured; D003124:Colorimetry; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D005960:Glucosides / Q000032:analysis; D009088:Mucoproteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D019897:Periplasm / Q000378:metabolism*; D010696:Phloroglucinol / Q000031:analogs & derivatives / Q000032:analysis; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D012965:Sodium Chloride / Q000494:pharmacology*; D014026:Nicotiana / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D015854:Up-Regulation
chemical_list: D005960:Glucosides; D009088:Mucoproteins; D010940:Plant Proteins; C104977:Yariv reagent; C006619:arabinogalactan proteins; D012965:Sodium Chloride; D010696:Phloroglucinol