IAA-dependent adjustment of the in vivo wall-yielding properties of hypocotyl segments of Vigna unguiculata during adaptive growth recovery from osmotic stress

Regulation of the in vivo yielding properties of the cell wall, namely cell wall extensibility (phi) and effective turgor (P-Y), of Vigna hypocotyl segments during adaptive recovery of growth after osmotic stress was investigated by successive measurements using the pressure-jump method. In the absence of IAA, cell wall extensibility (phi) showed no significant changes under osmotic stress but effective turgor (P-Y) reduced to near zero, resulting in no growth recovery. In the presence of 10 mu-M IAA, the cell wall extensibility was slightly decreased even when distinct recovery of growth took place in response to osmotic stress caused by 60 mM sorbitol. The effective turgor, however,showed a characteristic increase in contrast to the wall extensibility. It is not wall extensibility but effective turgor that regulates the cell wall yielding during the adaptive recovery of growth. In excised hypocotyl segments, however, reduced turgor would not be expected to recover, as has been observed in hollow cylinders. The results presented here suggest that the IAA-dependent adjustment of the yield threshold plays an indispensable role in wall-yielding for rapid adaptive growth recovery under osmotic stress