ACID-INDUCED CHANGES IN THE IN-VIVO WALL-YIELDING PROPERTIES OF HYPOCOTYL SECTIONS OF VIGNA-UNGUICULATA

Elongation growth of hypocotyl sections of Vigna unguiculata under xyl em perfusion was significantly enhanced when acid was applied by acid- aerosol to an abraded hypocotyl surface in the air. The in vivo wall e xtensibility (phi) and the effective turgor (P-i-Y), both of which wer e determined by the pressure-jump method, increased during acid-induce d growth as observed in IAA-induced growth. The intracellular pressure (P-i), however, decreased significantly at the beginning of acid-indu ced growth whereas P-i scarcely changed in IAA-induced growth. This re sult indicates that protons increase the effective turgor by decreasin g the yield threshold as IAA does. There seems to be no essential diff erence between proton and auxin in the effects on the in vivo mechanic al properties of the surface cell wall.