The role of wall calcium in the extension of cell walls of soybean hypocotyls.
Calcium crosslinks are load-bearing bonds in soybean (Glycine max (L.) Merr.) hypocotyl cell walls, but they are not the same load-bearing bonds that are broken during acid-mediated cell elongation.  This conclusion is reached by studying the relationship between wall calcium, pH and the facilitated creep of frozen-thawed soybean hypocotyl sections.  Supporting data include the following observations: 1) 2-[(2-bis-[carboxymethyl]amino-5-methylphenoxy)methyl]-6-methoxy-8-bis[carboxymethyl]aminoquinoline (Quin 2) and ethylene glycol-bis(2-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) caused only limited facilitated creep as compared with acid, despite removal of comparable or larger amounts of wall calcium; 2) the pH-response curves for calcium removal and acid-facilitated creep were different; 3) reversible acid-extension occurred even after removal of almost all wall calcium with Quin 2; and 4) growth of abraded sections did not involve a proportional loss of wall calcium.  Removal of wall calcium, however, increased the capacity of the walls to undergo acid-facilitated creep.  These data indicate that breakage of calcium crosslinks is not a major mechanism of cell-wall loosening in soybean hypocotyl tissues.
Virk
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SS
Department of Botany, University of Washington, Seattle 98195, USA.
Cleland
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RE
D000634:Aminoquinolines / Q000494:pharmacology; D002118:Calcium / Q000737:chemistry* / Q000502:physiology*; D002473:Cell Wall / Q000737:chemistry* / Q000187:drug effects / Q000502:physiology*; D002614:Chelating Agents / Q000494:pharmacology*; D004533:Egtazic Acid / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D018546:Hypocotyl / Q000737:chemistry / Q000187:drug effects / Q000254:growth & development*; D013025:Glycine max / Q000737:chemistry / Q000187:drug effects / Q000254:growth & development*
D000634:Aminoquinolines; D002614:Chelating Agents; D004533:Egtazic Acid; C035739:Quin2; D002118:Calcium