HbTIP1;1 in the inner bark tissues was significantly and strongly down-regulated at the transcription level by all three hormones 4 h after the ABA treatment and after 8 h following the auxin and SA treatments. Conversely, this gene was transiently up-regulated in the laticifers by three hormonal treatments, peaking between about 10- and 45-fold compared to the control at 4 h or 8 h ( Fig. 2D–F). In the inner bark tissues, auxin and ABA, but not SA, induced a slight up-regulation of HbPIP1;1; this up-regulation was significant and reached a plateau 8 h after the treatments. In contrast, HbPIP1;1 was significantly and transiently down-regulated in the laticifers, especially by auxin.