Periplasm turgor pressure controls wall deposition and assembly in growing Chara corallina cells.
OBJECTIVE
New wall deposition usually accompanies plant growth. External osmotica inhibit both processes but wall precursors continue to be synthesized, and exocytosis follows. Consequently, the osmotica appear to act outside of the plasma membrane. Because this implies an action of turgor pressure (P) on the periplasm by unknown mechanisms, the following study was undertaken to determine whether P could act in a way that altered wall deposition and assembly in the periplasm while the cells grow.


METHODS
Cells of Chara corallina were exposed to P slightly below normal by using a pressure probe while supplying inorganic carbon in light. After labelling, the walls were isolated and the amount of new wall was determined. Similar measurements were made after treatment with osmotica. Chlortetracycline-stimulated exocytosis was determined microscopically. Polysaccharide properties were determined by confocal microscopy and vapour pressure osmometry in an 'artificial periplasm' in isolated Chara cell walls, using labelled dextran as an analogue of hemicellulose, and polygalacturonate as pectin.


RESULTS
Rapid growth and wall deposition occurred at normal P of 0.5 MPa but both processes decreased when P was lowered 0.1 MPa. Inorganic carbon uptake and exocytosis were unaffected. In the artificial periplasm, normal P caused high polysaccharide concentrations and rapid polysaccharide entry into the wall, and gel formation in the pectin. Lowering P decreased entry and gel formation.


CONCLUSIONS
This is the first indication that normal P of 0.5 MPa can concentrate periplasmic polysaccharides sufficiently to cause cross-linking and gel formation in pectins while simultaneously fostering the entry of large polysaccharides into small interstices in the existing wall. This P-action would thicken the primary wall and form a smooth transition between the new and old structure, suggesting a molecular mechanism of wall deposition and assembly while the wall extends.
Proseus
Timothy E
TE
College of Marine Studies, University of Delaware, 700 Pilottown Road, Lewes, DE 19958, USA.
Boyer
John S
JS
D001639:Bicarbonates / Q000378:metabolism; D049108:Cell Enlargement; D002458:Cell Fractionation / Q000379:methods; D002473:Cell Wall / Q000378:metabolism* / Q000648:ultrastructure; D044784:Chara / Q000166:cytology* / Q000254:growth & development / Q000648:ultrastructure; D003911:Dextrans / Q000737:chemistry / Q000378:metabolism; D005089:Exocytosis / Q000502:physiology; D009997:Osmotic Pressure; D010368:Pectins / Q000737:chemistry / Q000378:metabolism; D019897:Periplasm / Q000737:chemistry*; D013347:Subcellular Fractions / Q000378:metabolism / Q000648:ultrastructure
D001639:Bicarbonates; D003911:Dextrans; D010368:Pectins