IAA-DEPENDENT ADJUSTMENT OF THE IN-VIVO WALL-YIELDING PROPERTIES OF HYPOCOTYL SEGMENTS OF VIGNA-UNGUICULATA DURING ADAPTIVE GROWTH RECOVERYFROM OSMOTIC-STRESS

Regulation of the in vivo yielding properties of the cell wall, namely cell wall extensibility (psi) and effective turgor (P'-Y), of Vigna h ypocotyl segments during adaptive recovery of growth after osmotic str ess was investigated by successive measurements using the pressure-jum p method. In the absence of IAA, cell wall extensibility (psi) showed no significant changes under osmotic stress but effective turgor (P'-Y ) reduced to near zero, resulting in no growth recovery. In the presen ce of 10 mu M IAA, the cell wall extensibility was slightly decreased even when distinct recovery of growth took place in response to osmoti c stress caused by 60 mM sorbitol, The effective turgor, however, show ed a characteristic increase in contrast to the wall extensibility, It is not wall extensibility but effective turgor that regulates the cel l wall yielding during the adaptive recovery of growth. In excised hyp ocotyl segments, however, reduced turgor would not be expected to reco ver, as has been observed in hollow cylinders (Nakahori et al, 1990), The results presented here suggest that the IAA-dependent adjustment o f the yield threshold plays an indispensable role in wall-yielding for rapid adaptive growth recovery under osmotic stress.