LANDRUM, JAMES VICTOR. Biology Department, Washburn University, Topeka, KS 66621. - Effects of hormones on wide-band tracheid expression in stems of Anacampseros (Portulacaceae).
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
Key words: anatomy, auxin, cytokinin, gibberellic acid, Portulacaceae, tracheid