Abstract
Key message Two modes of amphivasal vascular bundle formation were identified, which may help determine the rate of radial growth in Dracaena draco stem. 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 lm thick) revealed that rate of cambial activity influences the mode of vas- cular bundle formation and identified two distinct modes differing in terms of xylem (tracheid) differentiation. Strands of vascular parenchyma traversing the ring of tra- cheids within the amphivasal bundle are usually horizon- tally 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.
Highlights
The secondary growth of monocotyledonous plants is due to the activity of the monocot cambium
These initials of the monocot cambium undergo periclinal divisions that lay down derivatives that subdivide and differentiate to form cells of the ground tissue, or to form cells of the vascular bundles
The early and later stages were identified. The former stages involve only anticlinal and periclinal division of the vascular bundle mother cells, whereas the latter refers to a variety of events specific to vascular bundle formation, with cell division being more or less complete, as well as growth of and/or secondary cell wall deposition in tracheids, and the differentiation of phloem and vascular parenchyma cells
Summary
The secondary growth of monocotyledonous plants is due to the activity of the monocot cambium. This meristem is made up of one type of initial consisting of fusiform, rectangular or polygonal cells, arranged in a non-storied pattern (Cheadle 1937; Philipson et al 1971). These initials of the monocot cambium undergo periclinal divisions that lay down derivatives that subdivide and differentiate to form cells of the ground tissue (mainly centripetally), or to form cells of the vascular bundles (only centripetally). Only amphivasal bundles occur in Dracaena marginata and D. draco (Scott and Brebner 1893), whereas only collateral bundles occur in Y. brevifolia (Carlquist 2012)
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