• Journal of Plant Biology
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• v.27 no.3
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• pp.173-178
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• 1984

Callus culture of Phaseolus vulgaris L. was carried out to examine the ability to grow on cytokinin-free medium. Of the sixteen cultivars of P. vulgaris, eight were classified as completely cytokinin-autonomous phenotype and five were found to be cytokinin-dependent phenotype. Intermediate phenotype was shown in three cultivars. Using cv. Palgong and ca 21 as cytokinin-dependent genotypes, the genotype responses to the cytokinin requirements of callus tissue were studied in detail. The callus tissue of cv. Palgong and ca 21 were never habituated in cytokinin-free medium, regardless tissue origin and cytokinin concentration in previous passages. The result suggests that cytokinin dependency of callus tissue of P. vulgaris cv. Palgong and ca 21 may be due to inactivation of cytokinin biosynthetic pathway.

• Applied Biological Chemistry
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• v.29 no.1
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• pp.10-15
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• 1986

A polyacrylamide gel electrophoresis technique was applied to cytokinin-protein binding assay. Binding of soybean leaf proteins to cytokinin and relative affinities of protein fractions to cytokinin were studied. The electrophoresis technique appeared to be very useful for determination of cytokinin-protein binding, for identification of protein species binding to cytokinin and for comparison of relative affinities of the proteins to cytokinin. The presence of cytokinin-binding proteins in soybean leaves was confirmed from assays with ammonium sulfate precipitation, Sephadex G-25 chromatography, paper chromatography, and electrophoresis. Three groups of cytokinin-binding proteins were identified in the soybean leaf protein extract and two of the three showed low affinity to cytokinin, however, the third one with mobility between $0.0{\sim}0.2$, probably high molecular weight protein (s), showed high affinity in the electrophoretic analysis.

• Molecules and Cells
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• v.19 no.3
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• pp.342-349
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• 2005

Cytokinins are adenine derivatives that regulate numerous plant growth and developmental processes, including apical and floral meristem development, stem growth, leaf senescence, apical dominance, and stress tolerance. However, not much is known about how cytokinin biosynthesis and metabolism is regulated. We identified a novel Arabidopsis gene, ALL, encoding an aldolase-like enzyme that regulates cytokinin signaling. An Arabidopsis mutant, all-1D, in which ALL is activated by the nearby insertion of the 35S enhancer, exhibited extreme dwarfism with rolled, dark-green leaves and reduced apical dominance, symptomatic of cytokinin-overproducing mutants. Consistent with this, ARR4 and ARR5, two representative primary cytokinin-responsive genes, were significantly induced in all-1D. Whereas SHOOT MERISTEMLESS (STM) and KNAT1, which regulate meristem development, were also greatly induced, expression of REV and PHV that regulate lateral organ polarity was inhibited. ALL encodes an aldolase-like enzyme that belongs to the HpcH/HpaI aldolase family in prokaryotes and is down-regulated by exogenous cytokinin, possibly through a negative feedback pathway. We propose that ALL is involved in cytokinin biosynthesis or metabolism and acts as a positive regulator of cytokinin signaling during shoot apical meristem development and determination of lateral organ polarity.

• The Journal of Natural Sciences
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• v.10 no.1
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• pp.33-37
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• 1998

Cytokinin is one of major growth regulators in plants. In this study, the gene isopentenyl transferase (jpt) which encodes a key enzyme involved in the biosynthesis of the growth regulator cytokinin isolated from Agrobacterium tumefaciens was introduced ito tobacco plant via Agrobacterium-mediated transformation. The jpt gene was modulated using the proteinase inhibitor II (PI-IIK) promotor. In general, this promoterlipt gene fusion resulted in overproduction of cytokinins throughout the transgenic plants. The overproduction of cytokinin caused dramatic changes in morphology of the plant, including stem thickness and reduced root development. The studies reported in this paper were initiated to examine the consequences of overproduction of cytokinin in plant.

• Journal of Plant Biology
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• v.25 no.4
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• pp.161-168
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• 1982

The activities of auxins and cytokinins have been examined in the growth of callus tissue derived from Phaseolus vulgaris L. cv. Damyang. The synthetic auxin, picloram was the most effective in promoting callus growth and the range of effective concentrations (0.1$\mu{M}$ to 32$\mu{M}$) was broad. 2, 4-D also enhanced callus growth at the optimal concentration of 3.2$\mu{M}$. NAA promoted callus growth at relatively higher concentrations than other auxins tested. IAA was less effective in supporting callus growth. Cytokinin bearing saturated side chain ($N^6$-isopentyladenine) was approximately 30 times more active than the corresponding unsaturated compound, $N^6$-($\D^2$-isopentenyl) adenine. The abilities of cytokinin-autonomous growth were also examined. Callus tissues previously grown on concentrations lower and/or higher than optimal concentrations of cytokinins were better habituated in the subsequent passage. It was suggested that the development of cytokinin autonomy may be related to dosage-concentrations of cytokinin in the previous passage.

• Korean Journal of Agricultural Science
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• v.4 no.2
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• pp.121-125
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• 1977

The activity of endogenous cytokinin-like substance in dormant plants(Fragaria ananassa) was different depending on the degree of dormancy and their activity was showed the similar trend as that of growth phase. When strawberry plant crowns were extracted in methyl alcohol, and the extract was seperated by column chromatography, it showed that the activity was observed in two places by soybean callus bioassay. Activity of cytokinin-like substance was appeared when ethyl acetate/methyl alcohol (90/10v. and 50/50v.) were used. In relation to growth phase of strawberry plants, cytokinin-like activity increased at vigorous growth periods, whereas decreased in deep dormant period. However, cytokinin-like substance activity occurred again after strawberry plants passed through a certain chilling periods. Accordingly, it showed to have a negative correlation between the degree of dormancy and a mount of endogenous cytokinin-like substance.

• Molecules and Cells
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• v.28 no.4
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• pp.375-382
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• 2009

The 26S proteasome is a 2-MDa complex with a central role in protein turn over. The 26S proteasome is comprised of one 20S core particle and two 19S regulatory particles (RPs). The RPN12a protein, a non-ATPase subunit of the 19S RP, was previously shown to be involved in cytokinin signaling in Arabidopsis. To further investigate cellular roles of RPN12a, RNAi transgenic plants of RPN12a were constructed. As expected, the 35S:RNAi-RPN12a plants showed cytokinin signaling defective phenotypes, including abnormal formation of leaves and inflorescences. Furthermore, RNAi knock-down transgenic plants exhibited additional unique phenotypes, including concave and heart-shape cotyledons, triple cotyledons, irregular and clustered guard cells, and defects in phyllotaxy, all of which are typical for defective cytokinin signaling. We next examined the mRNA level of cytokinin signaling components, including type-A ARRs, type-B ARRs, and CRFs. The expression of type-A ARRs, encoding negative regulators of cytokinin signaling, was markedly reduced in 35S:RNAi-RPN12a transgenic plants relative to that in wild type plants, while type-B ARRs and CRFs were unaffected. Our results also indicate that in vivo stability of the ARR5 protein, a negative regulator of cytokinin signaling, is mediated by the 26S proteasome complex. These results suggest that RPN12a participates in feedback inhibitory mechanism of cytokinin signaling through modulation of the abundance of ARR5 protein in Arabidopsis.

• Journal of Plant Biotechnology
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• v.32 no.1
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• pp.15-21
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• 2005

The expression patterns of cyclin genes, which play a crucial role on cell cycle control, were analyzed with rice calli and leaf blades from seedlings. When callus was transferred from media containing the combinations of 2,4-D and kinetin under the dark conditions to medium supplemented with cytokinin-only on 7 days after the cultures, the expression levels of A-, B- and C-type cyclins from callus were increased significantly. Despite the fact that cyclin genes were well expressed on leaf blades rather than other organs in rice seedlings, rice leaf blades grown on the medium containing various combinations and concentrations of cytokinin for 24 hours had no major effect on the expression patterns of cyclins except zeatin. The relation between cytokinin regulation and the expression of cyclins of rice is discussed.

• Applied Biological Chemistry
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• v.35 no.6
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• pp.507-512
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• 1992

A ${\beta}-1,3-glucanase$ of soybean (Glycine max) was isolated, and the effects of benzyladenine(BA) on celluar levels of the enzyme content and activity were studied. The effects of BA on callose content in cell wall and wall regeneration of protoplasts were also studied to show promoting effect of cytokinin in cell wall regeneration and to elucidate action mode of cytokinin. The polypeptide of 21 kD was identified as ${\beta}-1,3-glucanase$, and the cellular content and activity of this polypeptide were decreased by BA treatment. The callose content in cell wall of callus and the wall regeneration of protoplasts were increased by BA treatment. These results indicate that cytokinin promotes cell wall regeneration by inhibition of callose degradation via decreasing ${\beta}-1,3-glucanase$ level in cell.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.48 no.1
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• pp.8-12
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• 2003

To find out the relationship between pod development and cytokinin contents during reproductive stage of peanut, the cytokinin contents, trans-zeatin ribo-side (t-ZR) and dihydrozeatin riboside (diZR), were investigated at 0, 7, 14, 21 and 28 days after flowering (DAF). The amounts of t-ZR and diZR in cotyledon and first branch among primary branches were 3, 448 pmol/g (FW) and 4, 824 p/g (FW), respectively, which were higher than those of other branches. The t-ZR and diZR contents of lower parts on the branch from cotyledon node at 7 DAF were 579 pmol/g (FW) and 2, 028 pmol/g (FW), respectively, which were higher than those of upper parts. The cytokinin contents of reproductive organs as flowering progressed were increased at 0 and 14 DAF on branch and position of node. The cytokinin contents of upper part with pruning the lower part on the branch from cotyledon node were high 112-337% at 7 DAF and 14 DAF compared with those of the control. In case of remove the upper part of the first internode on main axis, t-ZR contents was 4.7 times higher than diZR contents at 7 DAF. The pod setting rate of flower and position on the branch from cotyledon node was closely related to the cytokinin contents during floral reproductive stage.