Cytokinin production

Although roots, particularly the root apices, are a major site of cytokinin biosynthesis in plants, there is evidence now that other meristematic tissues and organs including the cambium, developing buds, seeds and fruits and the embryonic axis of germinating seed have the ability to synthesize cytokinins under optimal growth conditions [6, 14]. Recently, stem and leaves have also been shown to be additional sites of cytokinin production [6]. The view that root-produced cytokinins move in the xylem to the shoot to participate in the control of development and senescence is widely accepted [15]. The major question that remains to be clarified is under what conditions the observed cytokinin activity in other plant parts is derived solely from the roots, and when, and to what degree it is derived by synthesis in situ. 

Table 1. Physiological response and current commercial uses of gibberellin an cytokinin products registered in the USA and Europe...

The growth retardant CCC increases cytokinins in the bleeding sap of grape (Skene 1970). Skene has interpreted this as an indication that CCC acts directly on the root meristem to increase cytokinin production. However, since the effect of CCC is counteracted by GA, it is possible that the enhancement of cytokinin production by CCC is mediated by a CCC-induced reduction in GA. This indicates that GA may act to suppress cytokinin production in roots (Woolley and Wareing 1972 a), a possibility supported by Teltscherova (1970) who noted that CCC causes an increase in the cytokinin content of apical buds of Chenopodium rubrum and that GA can overcome this effect. lAA also reduces cytokinins in buds of Chenopodium, indicating that both GA and lAA may be involved in the regulation of cytokinin production in this material. 

Sinee eytokinins enhance GA levels and since GA appears to suppress cytokinin levels, the possibility of GA-mediated feedback inhibition of cytokinin production must be recognized. Also, the evidence that lAA can increase GA levels in apical buds of Chenopodium rubrum (Teltscherova 1970) indicates that the suppressing effect of lAA on cytokinin content may be a secondary effect mediated by GA. 

Syono K, Newcomb W, Torrey JG (1976) Cytokinin production in relation to the development of pea root nodules. Can J Bot 54 2155-2162... 

Sitton D, Itai C, Kende H (1972) Decreased cytokinin production in the roots as a factor in shoot senescence. Planta 73 296-300 Skene KGM (1967) Gibberellin-like substances in root exudate of Vitis vinifera. Planta 74 250-265... 

Benzylamine Purine. The purine 6-benzylaminopurine [1214-39-7] (13) is an analogue of the natural product adenine, a component of both deoxyribonucleic acid and ribonucleic acid. It is not employed alone, but rather in combination with the natural products GA and GA to improve the size, weight, and thereby, yield per hm of Red DeHcious apples (10,24,25). Compounds with cytokinin activity were reported in 1913 (26) and asymmetric growth in apples was pubHshed in 1968 (27). 

The sterols and sterolins in rice bran are potent immunomodulators. The best response was obtained with a 100 1 sterol/sterolin mixture that demonstrated T-cell proliferation from 20% to 920% and active cell antigens after four weeks in human subjects (Bouic et al, 1996). Another in vitro experimental study with sterol/sterolins, demonstrated a significant increase in cytokinines, interleukin-2 and y-interferon between 17% and 41 % in addition to an increase in natural killer cell activity. These experiments (Bouic et al, 1996) prove that sterol/sterolins are potent immunomodulators with important implications for the treatment of immune dysfunction. Rice bran products are excellent dietary supplements for the improvement of immune function. It is probable that the effects of rice bran on diabetes, CVD and cancer all result from improved immune function. 

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). 

Zearalenone was also found to be more effective than cytokinin treatment in inducing shoots in in vitro winter wheat production. Moreover, both zearalenone and cytokinins increased the activity of antioxidant enzymes in wheat callus undergoing regeneration, and it is very likely that they also stimulated the plant regeneration process (Szechynska-Hebda et al. 2007). The effectiveness of regeneration on media containing zearalenone shows the possibility of using zearalenone as an alternative hormone also to cytokinins in winter wheat callus culture. 

Plant growth regulators, 13 21-60, 284 carvone, 13 28 cytokinins, 13 28-30 ft-decanol, 13 30 dikegulac, 13 30 ethylene, 13 30-32 gamma aminobutyric acid, 13 32 gibberehins, 13 32-35 indole 3-butyric acid, 13 35-36 lactic acid, 13 36 natural product derivatives,... 

Mixed Cytokinins. The first cytokinin, kinetin [525-79-1] (3), was isolated from stale herring sperm (8) but, like so many biologically active natural products, it was later found in the vascular system of tobacco stems and leaves (9). Yeast also proved to have a very high titre of kinetin (see Yeasts) (8). The compound is very active in increasing cell division in tobacco wound callus tissue that has been cultured on White s agar medium supplemented with 2 mg/L of indole-3-acetic acid (IAA) [87-51 -4], The presence of IAA is mandatory to induce cell division in the presence of kinetin. 

The auxin and cytokinin, whose production is normally controlled, are now formed in large amounts and cause uncontrolled tumor growth. The opines are used by Agrobacterium as a unique source of energy and of metabolites for biosynthesis. The host plant cells, however, cannot catabolize the opines. 

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