title: Physical basis for altered stem elongation rates in internode length mutants of Pisum.
abstract: Biophysical parameters related to  gibberellin (GA)-dependent stem elongation were examined in dark-grown stem-length genotypes of Pisum sativum L.  The rate of internode expansion in these genotypes is altered due to recessive mutations which affect either the endogenous levels of, or response to, GA.  The GA deficient dwarf L181 (ls), two GA insensitive semierectoides dwarfs NGB5865 and NGB5862 (lka and lkb, respectively) and the  slender' line L197 (la crys), which is tall regardless of GA content, were compared to the wild-type tall cultivar, Torsdag.  Osmotic pressure, estimated by vapor pressure osmometry, and turgor pressure, measured directly with a pressure probe, did not correlate with the differences in growth rate among the genotypes.  Mechanical wall properties of frozen-thawed tissue were measured using a constant force assay.  GA deficiency resulted in increased wall stiffness judged both on the basis of plastic compliance and plastic extensibility normalized for equal stem circumference.  Plastic compliance was not reduced in the GA insensitive dwarfs, though lka reduced circumference-normalized plasticity.  In contrast, in vivo wall relaxation, determined by the pressure-block technique, differed among genotypes in a manner which did correlate with extension rates.  The wall yield threshold was 1 bar or less in the tall lines, but ranged from 3 to 6 bars in the dwarf genotypes.  The results with the ls mutant indicate that GA enhances stem elongation by both decreasing the wall yield threshold and increasing the wall yield coefficient.  In the  GA-insensitive mutants, lka and lkb, the wall yield threshold is substantially elevated.  Plants possessing lka may also possess a reduced wall yield coefficient.
authors.affiliation: Section of Plant Biology, Cornell University, Ithaca, New York 14853.
authors.forename: F J
authors.initials: FJ
authors.lastname: Behringer
authors.forename: D J
authors.initials: DJ
authors.lastname: Cosgrove
authors.forename: J B
authors.initials: JB
authors.lastname: Reid
authors.forename: P J
authors.initials: PJ
authors.lastname: Davies
mesh_terms: D055592:Biophysical Phenomena; D001703:Biophysics; D002473:Cell Wall / Q000378:metabolism / Q000502:physiology*; D017343:Genes, Plant; D005838:Genotype; D005875:Gibberellins / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D009997:Osmotic Pressure; D018532:Pisum sativum / Q000235:genetics* / Q000254:growth & development; D010937:Plant Growth Regulators / Q000378:metabolism*; D018547:Plant Stems / Q000235:genetics / Q000254:growth & development*; D013314:Stress, Mechanical; D013997:Time Factors
chemical_list: D005875:Gibberellins; D010937:Plant Growth Regulators; C007842:gibberellic acid