Table 1.
List of studied species from the family Commelinaceae, with respective sample voucher and collection locality.
Table 2.
Nomenclature for the vascular bundles.
Major bundle (sympodial vascular bundle that constitutes the internal vascular system), Minor bundle (sympodial vascular bundle that constitutes the external vascular system), Cortical bundle (sympodial vascular bundle which cross, through the cortex, more than one internode), Central bundle (internal non-sympodial vascular bundle), Cauline bundle (external non-sympodial vascular bundle).
Fig 1.
Illustration indicating vascular region (i.e., leaf bundle, leaf trace and axial bundle), and also represents the division of the shoot apex into phytomeres. Each phytomere consists of leaf, node, internode and lateral bud.
Fig 2.
Illustration indicating the course of the bundles along the shoot apex and the connections of the nodal vascular plexus, leaf, bud and adventitious root.
All major bundles (red) connect to the center of the vascular cylinder. The central bundles (orange) indicate the fusion of two or more bundles. The minor bundles have two similar trajectories. The first minor bundles (dark blue) run through the internode at a short distance from the pericycle (or continuous procambium with the pericycle), connecting to the vascular plexus of the node below, while the minor bundles of leaf margins (light blue) run through the internode adjacent to the pericycle (or continuous procambium with the pericycle). The other peripheral bundles (green) are the cauline bundles, which connect with each other or with minor bundles through the external nodal vascular plexus.
Fig 3.
Illustration of a longitudinal section of the sympodium.
Note division of vascular bundles in internal (red) and external systems (yellow). The internal system consists of major and central bundles. The external system is composed of minor and cauline bundles. Below the illustration, a transverse section of the 5th internode of the shoot apex of Commelina benghalensis L. shows the distribution of systems in an internode. The illustrations of leaves 1 and 2 represent two patterns of leaf venation. In illustration 1, only four minor bundles occur. In illustration 2, six bundles developed between the major bundles, two of them on each side of the midrib. Note that in both the illustration and the transverse section of C. benghalensis the minor bundle (white arrow) is slightly away from the pericycle (blue dotted line).
Fig 4.
3D reconstruction through manual segmentation of bundles and automatic segmentation of the parenchyma.
Image sequence of the nodal region of Tradescantia zebrina Heynth. ex. Bosse obtained in μCT. A) Rendered volume of all bundles, IVP and EVP. Major bundles and central bundles (red), minor bundles (blue), minor bundles of leaf margins (light blue), cauline bundles (green), lateral bud bundles (yellow) and internal and external nodal vascular plexus (light pink). B) Rendered volume only with vascular bundles and plexus. C-F) Transverse plane. C) Complete volume. D) Rendering only of the major and central bundles, plus plexus. Note that the EVP delimits the central cylinder, so the major bundles external to the plexus are in the leaf sheath. E) Rendering of the minor bundles plus plexus. F) Rendering of marginal minor bundles.
Fig 5.
In Tradescantia zebrina Heynh. ex Bosse (A-B) and Commelina benghalensis (C-D). Note the bifurcation connecting two bundles from the internode above to a bundle from the internode below in figure A (arrowhead). The inverse situation can be observed in figure B, where a bundle of the internode above connects to two bundles of the internode below (arrowhead). Colored digitally. In figures C and D, it is possible to observe the transverse and oblique connections in the external nodal vascular plexus (arrowheads).
Fig 6.
Analysis of vascular connections in the nodal vascular plexus region.
A) Longitudinal section of Tradescantia fluminensis Vell. in the IVP region showing tracheal elements at different stages of differentiation. B) Transverse section of Commelina benghalensis L. showing connections between the leaf traces and peripheral bundles (arrowhead). C-D) Transverse section of C. benghalensis analyzed in a confocal microscope. C) Leaf trace between two vascular bundles. Contrast with aniline blue and berberine hemisulfate indicated callose plates in the leaf trace, but plates were not present in the oblique and transverse connections between vascular bundles. D) Connections between the IVP and the EVP (arrows), and connections between the leaf trace (LT) and peripheral bundles (arrowheads).
Fig 7.
Anatomical variation of central vascular bundles.
Image sequence in order from left to right and top to bottom, showing the anatomical variation of central bundles crossing the IVP. In the upper region the bundles are collateral, but along the IVP they change to an amphivasal arrangement, returning to collateral when the next internode starts below. Traqueary elements (red doted line) and phloem (black doted line). Scale bars 100μm.
Fig 8.
Transverse sections of the stem of Commelina benghalensis L.
A) Nodal region of the second phytomere showing three unconnected procambial strands (black arrowheads). B) Nodal region of the third phytomere showing that there is still no fusion of the first three procambial strands (black arrowheads). C) Nodal region of the fourth phytomere indicating the first fusions of major bundles to the internal vascular plexus (red arrowheads). D) Nodal region of the fifth phytomere indicating primordia of adventitious roots. E) Internode region of the fifth phytomere showing digitally colored circles to indicate rings formed by each category of bundles. The most peripheral ring (green) consists of cauline bundles of the fifth phytomere and minor bundles from the fourth primordium. F) Illustration of figure (E) with bundles colored according to their respective category.
Fig 9.
Overview of the course of vascular bundles along the main axis of the stem.
A) Whole-mount diaphanization of the shoot apex of Tradescantia zebrina Heynh. ex Bosse. B) μCT analysis by contrast attenuation of the shoot apex of T. zebrina, contrasted with lead citrate. C) Illustration indicating the straight course of vascular bundles in the internode of Dichorisandra thyrsiflora J.C. Mikan.