Cytokinine activity

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). 

Occurrence, chemistry, synthesis and cytokinin activity of l -methyl-rran.s-zeatin and its analogs (glycosylated adenine derivatives) 97H(46)659. 

It is possible that, over these longer periods, protein synthesis is affected. Itai Vaadia (1965, 1971) showed that during water stress cytokinin activity in the root exduate and translocation of cytokinin were reduced. Ben-Zioni, Itai Vaadia (1967) showed that the lower rate of protein synthesis of stressed leaf tissue could be raised by treatment of leaf material with kinetin. We need more information on levels of various proteins after naturally occurring stress. 

Itai, C. Vaadia, Y. (1971). Cytokinin activity in water-stressed shoots. Plant Physiology, 47, 87-90. 

In connection with the cytokinin activity of N6-isopen-tenyladenosine,194 195 Leonard and coworkers196 prepared the N7-... 

Cytokinin activity can be assayed conveniently with several plant tissues, including soybean (54) and tobacco (55,56) callus, radish leaf discs (11,12) and lettuce seed (57). The first two of these are probably the most useful since they are not excessively sensitive to light or temperature (58,59) and reflect both cell enlargement and division (60). 

Compound 14, having the structural and growth-promoting characteristics expected of a potential anticytokinin, was tested for its ability to block the promotion of cell division and growth by other compounds having significant cytokinin activity. 

Figure 1. Cytokinin activities in the tobacco bioassay of 6-(3-methyl-2-butenyl-amino)purine (3), 6-isopentylaminopurine, and four (3-methyl-)7-alkylaminopura-zolo[4,3-d]pyrimidine (11-14)...

Cytokinin activity Growth inhibition, min. cone. (yM) for min. cone. (yM) for... 

The accumulated assay results obtained with the 4-alkyl-2-methylpyrrolo[2,3-d]pyrimidines are of special interest. Can-pounds 25 and 26 exhibited significant cytokinin activity in all assays utilized. On the other hand, compound 27 was a potent antagonist in the tobacco bioassay but had little activity in the other two assay systems, while 29 acted as an anticytokinin in the tobacco bioassay and a cytokinin in the lettuce seed germination assay, but was without activity in the Amaranthus test system. 

Many 6-alkylaminopurine nucleosides are important adenosine receptor antagonists, and acyclic nucleotide analogues derived from 6-dialkylaminopurines are strong antivirals, anti-neoplastic agents, and immunomodulators. Recently, several 6-(arylalkynyl)-, 6-(arylalkenyl)-, and 6-(arylalkyl)purines have been reported to exhibit cytokinine activity. Suzuki crosscoupling reactions of 9-benzyl-6-chloropurine with boronic acids have recently been reported to provide 6-substituted purines in moderate to excellent yields (Eq. (46)) [77]. 

Figure 16 Current model of cytokinin activation in higher plants.

Several studies have implicated a role for cytokinins in the regulation of both the Gj—S cycle418,463 and the G2— M phase transition417,464 of the cell cycle. Cytokinin activates Arabidopsis cell division through induction of D-type cyclin, CycD3, at the Gi—S cell cycle phase transition.463,465 A sharp increase in the levels of cytokinins was reported in tobacco cell cultures at the G2—M phase.417 Roots of multiple mutants of cytokinin receptor genes show delay of the transition in G -M phase.466... 

Takeshi Kuroha was born in 1977. He graduated from the School of Biological Sciences, University of Tsukuba in 1999. He obtained his Ph.D. degree from the University of Tsukuba in 2005. He studied the mechanisms of adventitious and lateral root formation in graduate school. In 2005, he joined the Biodynamics Research Team in RIKEN Plant Science Center as research associate and is involved in the study of enzymes related to cytokinin activation. His research interests concern genetic, biochemical, and molecular physiological studies on development, local and long-distance communication, and cytokinin biosynthesis in plants. 

Cytokinins are unique among plant hormones in that adenine compounds of identical structure occur in nucleic acids. More specifically, particular cytokinin-active ribonucleosides occur as components of certain molecular species of tRNA. Zachau et al. (19), during the determination of the base sequences of serine tRNA in yeast, first reported an "odd" base immediately adjacent to the 3 end of the anticodon. In collaboration with Biemann et al. (20), this "odd" base was identified as the natural cytokinin isopentenyl-adenosine, which is one of the most highly active cytokinins known. 

In the cases of wheat germ and etiolated bean seedlings, for examples, cytokinin-active ribonucleosides are limited to only tRNASer and tRNA eu. 

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