Kinetin auxin

Next to the amount of P, the chemical form of this nutrient (Lambers et al. 2002 Shu et al. 2005 Shane et al. 2008) and the availability of other nutrients, especially nitrogen, potassium, and iron (Shane and Lambers 2005) affects the formation of cluster roots. It seems to be regulated by several plant hormones. Thus, application of auxin led to the production of cluster roots in white lupin at P concentrations that normally suppress cluster roots (Gilbert etal. 2000 Neumann et al. 2000). Cytokinines might also play a role, as kinetin applied to the growth medium of P-deficient white lupin inhibited the formation of cluster roots (Neumann et al. 2000). 

In the presence of adenine and kinetin, orotic acid or thymine can enhance the production of flower buds in vitro in stem segments of Plumbago indica [ 187]. The production of buds is often inhibited by auxins and gibbereUns [ 188]. 

The induction of PAL activity by the two growth factors can be separated in time so that they may act at different sites within the cell to bring about the response (40). Auxin added at the time of subculture of the tissue changes the pattern of protein synthesis of the cells by changing the transcription pattern of the mRNA after two hours (43). Kinetin does not have this effect (44). 

Matthyssee and Phillips (20) isolated two nuclear proteins, from tobacco cells, that bound specifically to 2,4-D. Receptor proteins for auxins, kinetins, and GA have been found (21). Sub-cellular fractions from bean leaves were recently shown to bind abscisic acid (22). Preliminary experiments (22) indicated that maximum ABA binding activity coincides with the activities of membrane-bound Mg -dependent, K+-stimulated ATPase and glucan synthetase. Table I of Biswas and Roy (21) lists hormone receptor proteins reported in plant tissue. For a protein to qualify as a receptor molecule, it should have a high stereo-specific binding capacity (Kd 10 6 to 10 SM) for its particular hormone. In com coleoptiles, both IAA and NAA are equally effective in inducing cell elongations fractions of plasma membrane and endoplasmic reticular membrane contain receptor proteins with Kd values of 10 M to 10 M for auxins (5, 18). When one considers procedural... 

Classically, there are five main categories of naturally occurring PGR, the auxins (lAA, NAA, IBA, 2,4-dichlorophenoxyacetic add), gibbereHins (GA), cytoM-nins (kinetin, benzyladenin, zeatin), ethylene, and growth inhibitors like abscisic acid (ABA). 

Fig. 11.2. Chemical structures of plant growth regulator compounds out of the five main PGR categories auxins (lAA, 2,4-D), ethylene (ethephon), cytokinin (kinetin, benzyladenin), growth inhibitors (ABA), and gibberellins (GA3).

The interaction of lAA with another PGR, kinetin, which is a cytokin, has been observed by growing tobacco stem pith callus in tissue culture. Jablonski and Skoog (29) have reported that with a low cytokinin to auxin ratio in the tissue culture, the result is a mass of loosely arranged, undifferentiated cells or callus, but with a high cytokinin to auxin ratio, the result is the growth of cultured plantlets with stems and leaves. 

Secondary metabolites, produced by pathways derived from primary metabolic routes, are numerous and widespread, especially in higher plants. More than 20,000 were known in 1985 (Hartmann, 1985), and at least 1000 additional compounds, are described each year. In practice, the difference between the primary and secondary metabolites is fuzzy. Plant hormones such as gibberellic acid, indoleace-tic acid (auxin), ethylene, kinetin, and abscisic acid, as well as compounds involved in plant cell wall structure such as cinnamic acid and its polymeric derivative, lignin, are intermediate between primary and secondary metabolism (Birch, 1973). In some instances, compounds normally considered primary metabolites may accumulate in large amounts and behave in a manner usually associated with secondary metabolites. Entities such as shikimic acid and squalene, which initially were considered secondary metabolites, were subsequently shown to be important intermediates in the formation of primary metabolites (phenylalanine, tyrosine and tryptophan, and steroids, respectively). 

Seki, H., M. Takeda, K. Tsutsumi, and Y. Ushiki Callus Culture of the Mulberry Tree. I. Effect of Concentrations of Auxin and Kinetin on the Callus Culture of the Mulberry Stem. Nihon Sanshigaku Zasshi (J. Sericul. Sci. Japan) 40, 81 (1971). 

Recently, the isolation of gibberellin and kinin provided further proof for the coumarin-auxin relation. These substances are included among the plant hormones, although gibberellic acid, a representative of gibberellins, was first isolated as a fungal metabolite, and kinetin, the best known kinin derivative was produced from nucleic acids [119-121]. Both of these compounds, however, were also found in higher plants. 

Kinetin 6-furfurylaminopurine, the model substance for cytokinins. K., in conjunction with other factors, such as auxins, induces renewed cell division in resting plant tissue. It influences the nucleic acid and protein metabolism of the plant. In addition to many other physiological effects, it prevents yellowing of isolated leaves and promotes protein synthesis at its site of application. K. is obtained by hydrolysis of deoxyribonucleic acid. The 2-deoxyribose of the DNA provides the furfuryl residue of the K.It can also be made synthetically from 6-mercaptopurine and furfurylamine. 

Frenkel C (1972) Involvement of peroxidase and indoleacetic acid oxidase isozymes from pear, tomato and blueberry fruit in ripening. Plant Physiol 49 757-763 Fuchs Y, Lieberman M (1968) Effects of kinetin, lAA and gibberellin on ethylene production and their interactions in growth of seedlings. Plant Physiol 43 2029-2036 Fuente RK de la, Leopold AC (1972) Two components of auxin transport. Plant Physiol 50 491-495... 

Seth A, Wareing PF (1964) Interaction between auxins, gibberellins and kinins in hormone-directed transport. Life Sci 3 1483-1486 Seth AK, Davies CR, Wareing PF (1966) Auxin effects on the mobility of kinetin in the plant. Science 151 587-588... 

Wickson M, Thimann KV (1958) The antagonism of auxin and kinetin in apical dominance. Physiol Plant 11 62-74... 

Examples of antagonistic interaction include the effects of ABA and auxin on root tip surface charge (Tanada 1972) the effects of ABA and kinetin on coleoptile elongation (Khan and Downing 1968), the effects of GA and tannins on enzyme biosynthesis (Jacobson and Corcoran 1977) and the effects of ethylene and either GA3 or cytokinin on fruit senescence (Goldschmidt et al. 1977). 

Effects on Cytokinin, Gibberellin, and Auxin. Desiccation causes a reduction in the cytokinin activity of the root exudate of sunflower (Itai and Vaadia 1965) as well as the leaf tissue and xylem exudate of Nicotiana rustica (Itai and Vaadia 1971). In the experiments with Nicotiana there is evidence for a reversible chemical transformation of " C-kinetin as the means of altering cyto-... 

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. 

Kinetin promotes the formation of ethylene in the elongation zone of eorn roots. Although enhancement of ethylene production by kinetin is greater than by auxin, Svensson (1972) concluded on the basis of other data that ethylene does not mediate the inhibitory effect of kinetin on root elongation. A similar conclusion was reached by Dubucq (1976). 

Caspar and Xhaufflaire (1967) noted that kinetin-treated lentil roots have more lAA oxidase activity than control roots. They suggested that kinetin inhibition of root elongation may be due to a reduction in the auxin content of the root. This was supported by Darimont et al. (1971) who found that kinetin reduces the lAA content of lentil roots. 

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