The effect of shoot-bending on the amount of diffusible indole-3-acetic acid and its transport in shoots of Japanese pear

The amount of diffusible indole-3-acetic acid (IAA) in shoots of Japanese pear (Pyrus pyrifolia) decreased when vertical shoots were bent at an angle of 45 degrees. A significant decrease of diffusible IAA was observed one day after shoot bending (DAB), and the degree of this decrease was larger in the apical region of the shoot than in the basal region. The decrease caused by the shoot bending increased with the duration of the treatment. The IAA amounts in the bent shoot in the apical, central, and basal segments on 1 DAB were 58.2 +/-6.4%, 92.6 +/-7.6%, and 79.1 +/-7.1% of the control, while 43.7 +/-4.1%, 30.8 +/-2.9%, and 39.4 +/-2.5% on 14 DAB. Radiolabelled IAA transport velocity was also examined, but it was not influenced by the shoot angle in the apical region of the shoot. However, the IAA transport velocity in the basal region decreased. It dropped first on I DAB, but it recovered to the control level 3 DAB, then it decreased again on 14 DAB. A large increase in ethylene production was observed in the bent shoot, but it seemed transient and did not continue for 14 days. These results suggest that the decrease of diffusible IAA amounts may be induced not by the decrease of IAA transport velocity but by the production/supply of IAA in the apical region.