Wide-band tracheids (WBTs) are found in leaves and stems of species in the South African genus Anacampseros (Portulacaceae). Wide-band tracheids are parenchyma cells that are converted into modified tracheids with wide secondary walls intruding into the lumen. In stems, WBTs occupy rays and pith, and are thought to function as an alternative water-conduction system or water-storage system in severe water-stress conditions common to their location. Experiments were conducted to determine the effects of auxin, cytokinin, and gibberellic acid (GA) on WBT formation. Seedlings were grown on sterile sand medium inundated with hormone solution, and were harvested at 30 and 65 days. There was little difference between auxin-treated plants, kinetin-treated plants, and control plants; however, a significant difference was noted in seedlings exposed to gibberellic acid. In the GA seedlings, three of four measured traits remained similar with the exception of the cell area occupied by the wide-band, which increased from a mean of 72% in the control seedlings to a mean of 81% in the GA seedlings. The inability of auxins and cytokinins to change WBT characteristics implies that WBTs are not initiated by the same signalling pathways that usually activate tracheid production.

Key words: anatomy, auxin, cytokinin, gibberellic acid, Portulacaceae, tracheid