Anatomy of Nodes vs. Internodes in Coleus: The Longitudinal Course of Xylem Differentiation

Abstract

All xylem strands in Coleus are initiated and differentiated discontinuously and bidirectionally from each nodal region along the lengths of the strands. Within nodes, the strands are larger in transsectional area and contain a greater number of vessels, a greater proportion of vessel elements vs. xylary parenchyma cells, and vessels in more advanced stages of differentiation than in adjacent internodes. When xylem develops in bundles that initially are composed only of phloem, or in short, isolated strands, it is initiated within nodal regions. The increased xylogenesis in the nodal regions is suggestive of locally enhanced auxin levels. Experiments were conducted to determine whether the advanced state of nodal vessel differentiation is a function of auxin import to the node from the leaf pair inserted at that node or whether it is due to an effect in the node of auxin transport from another (distal) source. A combined result was indicated, as removal of a leaf pair led to a decline in nodal xylem differentiation in the side bundles but not the corner traces passing through the node from younger leaves. The effect of a leaf pair on side bundle xylem differentiation at the same node was replaceable by exogenous IAA application to the cut leaf sites.

Cell Determination During Embryogenesis in Citrus Jambhiri. Ii. Epidermal Differentiation as a One‐time Event

“…Embryos at different stages were treated in a similar manner. A slice was taken from the root-hypocotyl axis with custom-made scalpels (see Bruck and Paolillo, 1984, for description) under a Wild M-7 stereomicroscope in a transfer room. The slice was as small in area and as shallow (one to three cell layers) as possible.…”

Anatomy of Nodes vs. Internodes in Coleus: The Nodal Cambium

“…Delimitation of the node-Elongation was followed by examining the distortion and movement ofcircular spots (carbon-blackened stopcock grease; see Bruck, 1982, for details) on the surfaces of the plants. Stem elongation was arrested in a region shorter than the height ofthe leafbase at Node 5, and throughout Node 6.…”

“…The pattern ofelongation revealed by surface measurements was borne out by measurements of the height of pith cells in successive nodes and internodes ofa Coleus stem (Bruck, 1982). Internodal pith cells elongated until Internode 10, whereas elongation of nodal pith cells was lacking beyond Node 5.…”

“…Branches of the side bundle diverging at older nodes combined with bundles that lay along their path to the comer (Fig. 2, 3), including any xylem that developed opposite the phloem strands at Node 6 and older nodes (Bruck and Paolillo, 1984a). In Node 6, phloem bundles commonly branched along the sides ofthe stems alternating with the leaf bases.…”

“…For example, nonextensible (metaxylem) tracheary elements were reported in the nodes of Clematis and were continuous with extensible (protoxylem) elements in the adjacent internodes (Esau, 1965a). In Coleus, nodes were conspicuous because of a localized change in the size, maturity, and composition ofany vascular trace (Bruck and Paolillo, 1984a), and experimental modifications of vascular branching were usually inducible only in nodal regions (Bruck and Paolillo, 1984b, c). Therefore, a developmental study was conducted in Coleus to characterize nodes and compare them with internodes.…”