Secondary thickening

Figure 1. Developing secondary thickened wall of the hypocotyl of Phaseolus vulgaris. The section was treated with an antibody specific for / 1 — 4 linked D-xylose units and stained with gold-labelled goat-antirabbit serum. The label is seen at the secondary thickening (st) and the vesicles of the Golgi apparatus (v).

After a cell has matured, the wall may become thickened and take on a distinctive shape and specialized properties it is then called a secondary wall. Secondary thickening of plant cell-walls is particularly marked in... 

The process of differentiation that transforms primary cells into secondary cells is only partially understood. In such thick-walled cells as tracheids, fibers, and vessels in mature tissues, the greater part of the wall is made up of secondary thickening deposited after expansion of the primary wall has stopped. In cells that show localized growth (for example, tip growth), the secondary wall may well start to form in areas removed from the growing zone, while the latter is still active.2... 

In addition to cellulose, hemicelluloses are also laid down during secondary thickening. In angiosperms, these hemicelluloses are preponder-... 

Lignin, a phenolic polymer, is also incorporated into the wall during the secondary-thickening phase. This component permeates the spaces between the plant cells, thereby strengthening the tissue. Lignification is a result of enzymic dehydrogenation and subsequent polymerization of coumaryl, coniferyl, and sinapyl alcohols, the relative proportions of which differ in the lignins from different plants.23-28... 

Leaf-mesophyll cells have been isolated from perennial ryegrass 257 In temperate grasses, such as perennial ryegrass, the mesophyll cells appear to be homogeneous. They lie between the epidermal, or surface, layers of the leaf, and are responsible for photosynthesis. The mesophyll cells have thin walls, and retain the ability to differentiate, whereas the vascular, conducting cells have initially thin primary-walls which, unlike the mesophyll cells, may undergo secondary thickening in the stem with age. The mesophyll cells account for 10-... 

Mucilage is formed in plants in several ways, viz. either as a product of the protoplasm, as a disorganization product of some of the carbohydrates, as a secondary thickening or addition to the cell wall, or as a metamorphosis of it. In the first two cases the mucilage is called cell-content mucilage, in the last two, membrane mucilage. 

U.S. 5100657 (1992) Ansher-Jackson et al. (Procter Gamble) A mixture of conditioning agents silicone, cationic surfactant, and fatty alcohol nonionic long-chain alkylated cellulose ether as the primary thickener water-insoluble surfactant as a secondary thickener Provide cleaner hair conditioning does not have the dirty hair feel and quick resoiling of hair associated with quaternary ammonium... 

Lignin is a very complex aromatic polymer deposited during secondary thickening of cell walls. Due to its complex nature it is difficult to determine accurately the lignin content of cell walls (Sarkanen and Ludwig,... 

Figure 6.3 Structure and Deposition of the Cell Wall of a Higher Plant. The scheme is A. The cell plate is laid down, after cell division, as the first stage of wall assembly. B. Primary wall deposition during cell enlargement. C. Secondary wall deposition, at the time of secondary thickening. In each case the plasmalemma underlies the material most recently laid down, i.e. secondary wall is internal to primary wall, c, cell plate m, middle lamella p, primary wall s, secondary wall. For further details see the text.

Some cells will divide further and, in these, the wall does not undergo secondary thickening. Others are committed to become specialised cells, such as xylem vessels or the sieve tubes of phloem, and these will undergo further change in their cell walls and will not, again, divide. 

The composition of the root oil seems to be varying with the age, too. Although there are hardly any reports on this issue, it seems that this variability may be the result of structural transformations. Stahl-Biskup and Wichtmann (1991) detected a decrease of germacrene B, the characteristic compound (in 51%) of the seedlings parallel with secondary thickening of the roots and formation of secondary oil cavities. The roots of adult plants contained mainly aliphatic aldehydes up to 68% of the oil. In the contrary, the herb oil of seedling and adult plants did not differ signi candy from each other. 

Figure 40.9 Transverse serial sections of a specimen of Anarhynchia gabbi Ager. Early Jurassic, Bedford Canyon, Santa Ana Mountains, California, MS 1687, showing development of ventrally directed and ventrally arching crura anteriorly (sections 1.6-14.1), flat cardinal process (0.4) and teeth laterally inserted in sockets (1.6). The appearance of septalial plate-like developments from the crura to the floor of the brachial valve are only briefly seen (0.6, 0.8) and then weak remnants are seen on the floor of the valve (1.6). This structure is so small that it does not appear to be a double median septum or septalial plates, but a secondary thickening of shell material towards the posterior of the valve, below the crura. This same resemblance to a double septum is more clearly seen in Ager s sections (1968, fig. 7). Dimensions of specimen length 29+ mm width 31.4+ mm thickness 15.1 mm. Scale bar is 3 mm for sections 0.0-1.6 6.25 mm for sections 2.1 -14.1 I mm for details of crura (bottom row) 6.5-10.1.

Polysaccharides containing D-xylose residues are present in the cell walls of practically all land plants, and are particularly abundant in plant tissues which have undergone secondary thickening (Fig. i, p. 205). Crude hemi-BMiography p. 231... 

Stem cuttings root easily and produce an extensive fibrous root system. Tubers are developed by secondary thickening of the roots near the base of the stem about 18 months after planting. Normally,... 

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