Root meristems auxin

In tomato root meristems, auxin causes an increase in the number of longitudinal and a decrease in the number of transverse divisions (Hughs and Street 1960), while in intercalary meristem segments from Avena stems, kinetin enhances transverse cell division and causes a shift of division within the intercalary meristem from the transverse to the longitudinal direction (Jones and Kaufman 1971). These effects were obtained only with high levels of kinetin. 

In nature, auxins are produced in apical and root meristems, young leaves, seeds and developing fruits, and their main functions are cell elonj tion and expansion, suppression of lateral buds, etc. (Opik RoUe, 2005). In somatic embryogenesis this is considered one of the most important elements producing cell polarity and asymmetrical cell division. In general, relatively high auxin concentrations (2,4-D, lAA, etc.) favor callus formation and the induction process (cell polarity). Afterwards, when the induction stage has been achieved, it is necessary to reduce or eliminate the auxins in order to initiate the bilateral symmetry and the expression of the somatic embryos. 

Although auxin is required for cell division, it increases the duration of the mitotic cycle in the root meristem of Vicia faba (MacLeod and Davidson 1966, Davidson and MacLeod 1966) and at higher concentrations suppresses mitosis completely in onion root meristem (Nagl 1972). In the liverwort, Riella helicophylla, anti-auxin treatment accelerates division, presumably by reducing the effective endogenous level of auxin (Grotha 1976). 

Barlow PW, Macdonald PDM (1973) An analysis of the mitotic cell cycle in the root meristem of Zea mays. Proc Roy Soc Lond B 183 385-398 Basrur SV, Fletcher RA, Basrur PK (1976) In vitro effects of 2,4-dichlorophenoxy acetic acid (2,4-D) on bovine cells. Can J Comp Med 40 408-415 Batra MW, Edwards KL, Scott TK (1975) Auxin transport in roots Its characteristics and relationships to growth. In Torrey JG, Clarkson DT (eds) The development and function of roots. Academic Press, London New York, pp 299-325 Beasley CA, Ting IP (1973) The effects of plant growth substances on in vitro fiber development from fertilized cotton ovules. Am J Bot 60 130-139 Beasley CA, Ting IP (1974) Phytohormone effects on in vitro cotton seed development. 

Sharma PK, Baruah P (1975) Effect of auxins on yeast. Nucleus 18 124-128 Shen-Miller J, McNitt RE, Wojciechowski M (1978) Regions of differential cell elongation and mitosis, and root meristem morphology in different tissues of geotropically stimulated maize root apices. Plant Physiol 61 7-12... 

Fig. 2. MTs in cells of ev. Alarik maize roots after their treatments either with the auxin transport inhibitor naphthylphthalamic acid (NPA) (100 pM, 6 h) (a-g) and with lAA (100 pM, 24 h) (h-j). After NPA treatment, periclinal divisions were induced in the outer cortex (a, thin arrows indicate young cell walls, thick arrow indicates pre-prophase band of MTs). Cells of the epidermis preserved well-ordered transverse CMTs both near the root apex (b) and in the transition zone (g). On the other hand, cells of the root cap (c), outer cortex (d), inner cortex (e) and of the stele parenchyma (f) showed disturbances to their general appearance and ordering (compare with Figs. 3c, d, g, h). Similarly to NPA treatment, relatively well-ordered transverse CMT arrays are still preserved in postmitotic cells of the epidermis (h) as well as in all cells of the former meristem (i,j) after the auxin treatment. Abbreviations EP, epidermis IC, inner cortex OC, outer cortex RC, root cap.

Auxin-transport inhibition was recently reported to interfere with the normal course of cellular development in the root apex. Roots of the tir3 mutant of Arabidopsis are believed to be affected in this way [79]. The primary root of the mutant has a meristem twice the length of wild-type (500 p,m compared to 250 p,m), suggesting that an altered auxin distribution within the root apex permitted more cells than normal to remain in a... 

The axrl mutants are deficient in most and perhaps all growth processes believed to be mediated by auxin, including meristem function, tropic responses and root hair elongation [60,61]. 

L-Tryptophan derivatives 3-Indoleacetic acid (D 21) and related compounds, e.g., indoleacetoni-trile (D 9.4) Plants (Apical meristems of stems and roots) Regulation of various growth and developmental processes (auxin activity)... 

The new growth hormone clearly controlled the linear growth of the grass coleoptile and its tropic curvatures were the outcome of an unequal distrihution of the hormone induced hy various unilateral stimuli. Quickly, evidence accumulated that auxin was universally distributed in higher plants. Secreted hy the apical meristems of hoth shoots and roots it controlled in these organs the expansion of the tissue cells. Further, its physiological activities were not confined to the control of cell expansion. It was implicated in apical dominance... 

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