Auxin division

NT433 Nishinari, N., and T. Yamaki. Relation between cell division and endogenous auxin in synchronously-cultured tobacco cells. Bot Mag (Tokyo) 1976 89 73. 

Cytokinins were discovered in the 1950s. In combination with auxin, they control cell division, promote juvenility or slow ageing and induce the formation of lateral buds (Figure 5.3). 

The cambium layer of plant stems (Fig. 1-16) differentiates continuously to form phloem on the outside of the cambium and xylem on the inside. At the same time, cambium cells are retained. Thus, at each cell division one daughter cell becomes a differentiated cell, while another remains the less differentiated cambium. This pattern of continuous differentiation from a line of stem cells with constant properties is found in animals as well as in plants. In the differentiation of cambium it appears that chemical signals obtained from the surrounding cells on either the inside or the outside of the cambium layer determine whether the differentiated cell becomes phloem or xylem. Sucrose, auxin, and cytokinins are all involved. 

Tn its normal polar, downward movement, the auxin stimulates the cells below the tip to elongate and sometimes to divide. Specific tissues, notably the cambium, are caused to divide laterally by auxin coming from the developing buds, which accounts for the wave of cell division occurring in tree trunks in the spring. Stimulation of other stem cells to divide... 

That gibberellin alone would produce normal cell division and enlargement in potato buds remains to be seen, as does a clear demonstration that the rise in level of endogenous gibberellins actually precedes sprouting. Whether the increase in gibberellin precedes the reported increase in auxin as rest terminates is also of... 

Gibberellin, Auxin, and Growth Retardant Effects upon Cell Division and Shoot Histogenesis... 

Figure 3. Development of BS and BI cellulase activity in apices of pea seedlings. Intact seedlings were sprayed with the auxin analogue 2,4-D and decapitated seedlings were painted with the natural auxin IAA with or without an inhibitor of DNA synthesis, FUdR. All treatments resulted in massive swelling at the pea apex because of cell expansion cell divisions also occurred, but not in the presence of FUdR (6). Cellulases were extracted as described in Figure 1 and assayed in unpurified form.

There had been good evidence for the existence of a cell division hormone (Figure 2d) since 1895 when Haberlandt first showed that slices of kohlrabi or potato tubers would, within a few days, form a new corky layer on the cut surface which was preceded by active cell division of several cell layers below the damaged cells. However, if the slices were well washed after the initial cutting, so that all traces of the damaged cells were removed, the divisions and corky layer failed to form—but would do so if crushed cells were re-applied (for summary see Haberlandt, 1921). This was not one of the properties of auxin. 

Efforts may now have been successful Whereas normal tobacco cells require auxin for division, sequence tagged (TDNA) lines encoding an adenylyl cyclase were obtained which were auxin-independent but cAMP-dependent. From one line (axi 141), a complementary DNA encoding adenylyl cyclase has been isolated with characteristic leucine repeats and similarity to yeast adenylyl cyclase (Ichikawa et al., 1997). The result seems not to be the expression of an alternative division pathway from the normal auxin-driven division since it is blocked by auxin inhibitors and is activated by cAMP and the cyclase activator forskolin. Perhaps a link to G-protein at the membrane will now bring plant growth regulation even closer to that of animals. 

Adamson, D., Expansion and division in auxin-treated plant cells. Can. J. Bot., 40, 719-744, 1962. 

Tuber dormancy studies can be separated into three general types based upon the tuber material used and whether the dormancy requirement is fulfilled naturally or via an artificial induction of cell division. Each method has distinct advantages and disadvantages. The tuber material includes intact tubers, tuber slices in which cell division is induced using an auxin analogue in an aqueous... 

Auxin-like responses, exudates, and initiation of adventitious roots affected. Cell elongation and division promoted or inhibited. Geotropic response lost. 

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