Formation of amphivasal vascular bundles in Dracaena draco stem in relation to rate of cambial activity

Abstract

Key message: Two modes of amphivasal vascular bundle formation were identified, which may help determine the rate of radial growth inDracaena dracostem. Abstract: Secondary growth of monocotyledonous plants results from monocot cambium activity. This lateral meristem gives rise to secondary tissues, i.e., secondary xylem and phloem arranged in vascular bundles, as well as the ground tissue that surrounds them. The aim of this study was to investigate the formation of vascular tissues relative to cambial activity in Dracaena draco stem. Based on the arrangement of mature amphivasal vascular bundles adjacent to the monocot cambium, regions differing in cambial activity were identified and sampled. Analysis carried out on transverse sections (3 µm thick) revealed that rate of cambial activity influences the mode of vascular bundle formation and identified two distinct modes differing in terms of xylem (tracheid) differentiation. Strands of vascular parenchyma traversing the ring of tracheids within the amphivasal bundle are usually horizontally orientated. It is proposed, that owing to its location, the developing vascular bundle may function in phloem unloading before maturation of tracheids is completed. Dracaena draco is a promising object for investigating seasonal response of radial growth in monocot stems, the modes of amphivasal vascular bundle formation being a helpful tool.