Aerial Root Structure and Its Significance for Function in Dracaena draco

Abstract

The dragon tree, Dracaena draco, is a vulnerable species. In response to stress it forms aerial roots (AR). Although the exact function of these AR is unknown, it has been the subject of speculation on the basis of morphological observations. This study aims to investigate the structural organization of the D. draco AR compared to the background of the structure of its soil roots. The material was obtained from the collection of dragon trees growing at Jardín Botánico Canario "Viera y Clavijo" on Gran Canaria as well as from the plants obtained from the commercial nursery. Based on hand-cut sections and permanent preparations, we analysed (a) AR structure along its length encompassing the active and dormant state of the AR tip, as well as (b) the general structural organization of the soil roots (stem-borne, lateral and fine roots). We observed that AR are similar to the lateral soil roots in terms of the distribution of the primary and secondary tissues. AR are protected by rhizodermis and/or hypodermis which undergoes metacutization during the transition from the active to dormant state of the AR tip. Chloroplasts are present in cortical parenchyma cells along the entire length of the AR. The obtained anatomical findings are discussed in the context of the putative AR functions.