protoxylem


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Related to protoxylem: metaxylem

protoxylem

the first XYLEM to differentiate from the primary MERISTEMS, with annular (ring-like) and spiral bands of thickening on the walls. Although dead, the cells are able to elongate as the adjacent cells grow in length. Protoxylem differentiates eventually into METAXYLEM.
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a Primary xylem pole of a main vascular bundle in transverse section; protoxylem elements collapse, leaving uniscriate rings of axial parenchyma, b Area between main bundles in which secondary xylem forms from interfascicular cambium without primary xylem formation, c Transverse section of secondary xylem; a narrow band of latewood is present, d Radial section of terminal latewood.
Epidermis (Ep), hypodermis (Hi), exodermis (Ex), cortex (Co), endoderm (En), aerenchyma (Ae), metaxylem (MX), protoxylem (PX) phloem (Ph), pericycle (Pe) and parenchymatic marrow (Ma).
Cells of adaxial and abaxial hypodermis similar to that of the lamina; colorless parenchyma located in the inner part with the collateral vascular bundles, these including xylem, vessels of protoxylem and metaxylem, xylematic parenchyma and fibers; phloem is composed of sieve cells and phloematic fibers.
Quantitatively evaluated were the following: (1) thickness of the foliar mesophyll; (2) thickness of the group of fibers from the foliar rib; (3) average diameter of the central vascular bundle of the foliar blade; (4) thickness of the cuticle; (5) size of the bulliform cells; (6) root diameter; (7) thickness of the root epidermis; (8) count of the poles of protoxylem; and (9) the diameter of the vascular cylinder of the root.
Vessel diameter increases from protoxylem into secondary xylem, then decreases again as secondary growth proceeds to cessation.
In the root and collet region, each primary xylem bundle breaks into a median protoxylem and a pair of metaxylems, and in this portion a pith begins to appear (Figure 2E, F).
Faint Casparian bands are first visible on the uniseriate exodermis radial walls, and a lignified, very small-celled, inner hypodermal sclerenchyma layer (SC) and protoxylem poles appear at 10 mm (Figure 1(b)).
Abbreviations used in the figures in this study: 1 = primary xylem; 2 = secondary xylem (wood); A = aperture of bordered pit; C = vascular cambium; M margo; MX = metaxylem; P = pith; PB = pit border; PH = phloem; PM = bordered pit membrane; PX = protoxylem; R = ray; S sclereids; T = torus; TR = tracheid; TY = tyloses; V = vessel member.
Dynamics of heterorhizic root systems: protoxylem groups within the fine-root system of Chamaecyparis obtusa.
primary xylem: Derived from procambium and divided into the earlier protoxylem and the later metaxylem.
Auxin is responsible for controlling the process of cell elongation and growth and differentiation of primary and vascular tissues, such as metaxylem and protoxylem (Aloni et al., 2006).