Differentiation tracheary cells

The note by Wareing (1958), reporting no differentiated tracheary cells from added GA3, some from lAA, but more when GA3 was added with lAA, to excised sections of tree stems, was extended in later papers. For five genera, Wareing et al. (1964) found the maximal width of new secondary xylem and phloem tissue when lAA and GA were added together to excised pieces of stem (Fig. 4.12). The cells considered to be on the phloem side of the cambium did not differentiate into sieve tubes or companion cells, however, whether they resulted from GA alone or GA plus lAA. lAA added alone resulted in some tracheary cells but no phloem cells. Kinetin, whether added alone or with IA A, was said to be without effect or perhaps slightly inhibitory. The... 

A major advance made since the 1965 edition of the volumes lA-16 on developmental physiology in the first series of this Encyclopedia was prepared has been the quantitative elucidation of hormonal control of sieve-tube differentiation during regeneration in stems. In addition, the earlier quantitative studies of tracheary differentiation have been extended and amplified. An unexpectedly close connection between sieve tubes and tracheary cells in their regeneration and normal differentiation has been revealed and a unifying picture of vascular differentiation in the shoot has resulted. A start has recently been made in unraveling the controlling factors for fiber differentiation. These advances will be described and discussed below. 

These first quantitative studies of cell differentiation under the influence of hormones are among the few cases in the literature where exact substitution of synthetic hormone for the normal hormone source has been demonstrated to give full and exact replacement of the hormone source in terms of a physiological effect. The prevention of abscission by lAA is another such case (Chap. 8 in Jacobs 1979). In both cases, the full effect of the leaves was replaceable by lAA alone. The results confirmed the hypothesis that, of all the chemicals undoubtedly required to differentiate a strand of regenerated tracheary cells, lAA from the leaves was the one that acted as a limiting factor in the process. Furthermore, the results with the polarity of the stem (Fig. 4.2) supported the view that the ability of the stem to transport lAA was a further check on how much lAA reached the regenerating area (Jacobs 1954). 

In his elegant study of hormonal control of the normal differentiation of phloem fibers (described below), Aloni (1976) pointed out that the fibers did not differentiate from the parenchymatous cells of the wound callus, even though sieve tubes and tracheary cells did. The differentiation of phloem fibers was always limited to the longitudinal vascular strands, never being found in the intervening parenchyma. In that sense, one could say that they do not regenerate however, their regeneration has been seldom studied. 

Wangermann (1967) excised Coleus leaves and found that fewer tracheary cells differentiated in the trace to the excised leaf, thus confirming, but with convincing quantitative data, the much earlier report of JosT (1893) on Phaseo-lus. The entire effect of the leaf on normal tracheary differentiation she found... 

The role of lAA in controlling the differentiation of tracheary cells (and to the much smaller extent that they have been studied, of sieve cells) seems well established. At least part of the role of other hormones (e.g., GA, ABA, cytokinins) in tissue differentiation is doubtless due to their demonstrated effects on the transport or available level of lAA. Whether they have more direct effects on cell differentiation is yet to be proven. 

Fig 6 Immunodot-blots of culture-medium aliquots sampled during the time-course of differentiation of Zinnia mesophyll cells to tracheary elements and dotted on to nitrocellulose. I = Inductive medium, N = Non-inductive medium. The JIM 7 epitope dries in a series of concentric rings on the nitrocellulose, indicating a mixed population of pectins. During the time-course, the rhamnose content of inductive culture medium increases dramatically compared with non-inductive medium. 

Stacey, N.J., Roberts, K., Carpita, N.C., Wells, B. and McCann, M.C. (1995) Dynamic changes in cell surface molecules are very early events in the differentiation of mesophyll cells from Zinnia elegans into tracheary elements. The Plant Journal, in press. 

As a plant grows in diameter, secondary xylem is formed from the cambium. Auxin has been implicated in the control of both cambial division and the subsequent differentiation of tracheary element [47]. When vascular bundles are broken, parenchyma cells can redifferentiate into tracheary elements and restore the functional bundles this occurs in response to elevated auxin levels at the wound site [39]. 

Lang and Kohlenbach (503) studied the differentiation of alkaloid cells in mesophyll protoplasts from M. microcarpa and M. cordata. In cell clusters which developed from protoplasts, cytodifferentiation into alkaloid cells and tracheary elements was observed. It was concluded that the alkaloid cells themselves produced the accumulated alkaloids. 

Haigler C.H. and Brown, Jr. R.M., 1986. Transport of rosettes from the Golgi apparatus to the plasma membrane in isolated mesophyll cells of Zinnia elegans during differentiation to tracheary elements in suspension culture. Protoplasma 134 111-120. 

Ingold E., Munetaka S., and Komamine A. 1988. Secondary cell wall formation changes in cell wall constituents during the differentiation of isolated mesophyll cells of Zinnia elegans to tracheary elements. Plant Cell Physiol 29 295 303. 

Iwasaki T, Shibaoka H (1991) Brassinosteroids act as regulators of tracheary-element differentiation in isolated Zinnia mesophyll cell. Plant Cell Physiol 32 1007-1014... 

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