Topic
Zeatin
About: Zeatin is a research topic. Over the lifetime, 2467 publications have been published within this topic receiving 64092 citations. The topic is also known as: Zeatin & (E/Z)-zeatin.
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TL;DR: The results contradict the hypothesis of de novo synthesis of cytokinins in roots of intact bean plants and find strong indications for their dependency.
Abstract: Roots of intact bean plants were supplied with [14C]adenine by pulse-chase experiments. The rate of incorporation of radioactivity into tRNA and oligonucleotides of roots as well as the content of radioactive labeled cytokinin nucleotides in these RNA fractions were determined. On the average, 1/70 of the radioactivity incorporated into tRNA was localized in N6(Δ2isopentenyl)adenosine. The half life of tRNA was estimated to be 65–70 h. Shortly after the pulse period, oligonucleotides contained zeatin riboside at a ratio of 1:800, on the basis of radioactivity. The half life of these oligonucleotides was determined to be about 8 h. The main free radioactive cytokinin of roots and leaves was zeatin. Comparing the rate of degradation of 14C-labeled tRNA and the oligonucleotides of roots and the rate of appearance of radioactive cytokinins in roots and leaves, we found strong indications for their dependency. The results contradict the hypothesis of de novo synthesis of cytokinins in roots of intact bean plants.
33 citations
TL;DR: A comparison of the cytokinin pattern in transgenic and wild-type plants indicates that these specific metabolites accumulate as a consequence of enhanced cytokinIn biosynthesis, and are probably involved in the homeostatic mechanisms that control endogenous cytokin in plants.
Abstract: Two novel cytokinin metabolites were identified in transgenic Arabidopsis thaliana (L.) Heynh. plants containing the bacterial IPT gene under the transcriptional control of a heat-regulated promoter. After cyclic heat-shock treatment, the endogenous cytokinin concentrations were elevated up to 100-fold compared to the wild-type plants. More then 20 different cytokinin metabolites were found, with zeatin-type cytokinins being the most abundant. The metabolic inactivation of these compounds occurred predominantly through N-glucosylation. No significant accumulation of isopentenyladenine-type cytokinins, and only a small increase in dihydrozeatin metabolites, was observed. Subsequent studies of the abundant, unidentified conjugates revealed the presence of zeatin and dihydrozeatin diglucoside conjugates. Structural analysis, utilizing electrospray-liquid tandem mass spectrometry, identified these as a zeatin-O-glucoside-9-glucoside and dihydrozeatin-O-glucoside-9-glucoside, respectively. A third unknown metabolite, was tentatively identified as a phosphorylated form of zeatin-9-glucoside. The biological activity of these compounds in three cytokinin bioassays was low. A comparison of the cytokinin pattern in transgenic and wild-type plants indicates that these specific metabolites accumulate as a consequence of enhanced cytokinin biosynthesis, and are probably involved in the homeostatic mechanisms that control endogenous cytokinin levels.
33 citations
TL;DR: The results strongly indicate that the latter increase is due to cytokinins originating from the Leaves of Yucca inflorescences.
Abstract: The origin of cytokinins in the exudate of Yucca inflorescences has been studied. A decrease in nucleotides of both isopenlenyladenine and zeatin was observed after removal of leaves as measured over a three day period. Removal of roots and the greater part of the rhizome resulted in a transient decline of isopenlenyladenincand zeatin nucleotides during 24 h. after which an increase took place. The results strongly indicate that the latter increase is due to cytokinins originating from the leaves.
33 citations
TL;DR: The capacity of zeatin-treated cotyledons to take up water more rapidly than controls and thus expand faster must be due to wall loosening, as reflected in psi(p) values which declined during 3 days from about +11 bars to about +1.4 bars.
Abstract: Water potential (ψ), the osmotic potential (ψ π ), and the pressure potential (ψ p ) of detached cotyledons isolated from Cucumis sativus L. cv Marketer seedlings after 0, 1.5, and 3 days growth with and without zeatin were determined. From zero time to 3 days, cotyledons incubated without exogenous zeatin exhibited a slight decrease in ψ (from −0.4 to −1.0 bars), while those grown with zeatin developed even more negative values (about −4 bars). Both groups showed rising ψ π values (decreases in solutes per unit volume), but this rise was more dramatic in those treated with zeatin. These data indicate that the capacity of zeatin-treated cotyledons to take up water more rapidly than controls and thus expand faster must be due to wall loosening, as reflected in ψ p values which declined during 3 days from about +11 bars to about +1.4 bars. It was also found that freshly detached cotyledons or those grown without exogenous zeatin exhibited osmoregulation in polyethylene glycol (PEG) solutions. That is, while cotyledons initially lost H 2 O into certain PEG solutions, their ψ values decreased over time and they began absorbing water after 1 to 4 hours. After 3 days growth, zeatin-treated cotyledons had lost most of this capacity of osmoregulate. It seems likely that osmoregulation in cotyledons not treated with zeatin is due to wall loosening rather than changes in ψ π . Zeatin-treated cotyledons with already loosened walls may not have this option to deal with water stress and thus simply come to equilibrium with external PEG solutions.
32 citations
TL;DR: Leaf explants of two Phalaenopsis species were used to test the effects of auxins, cytokinins, GA3, ancymidol, polyamines and polyamines on direct embryo formation on different leaf locations, and it was shown that the cut end showed highest embryogenic response, the adaxial side was the second, and then the abaxial Side and the leaf tip.
Abstract: Leaf explants of two Phalaenopsis, P. amabilis and P. Nebula, were used to test the effects of auxins (2,4-D, IAA, IBA, NAA), cytokinins (2iP, BA, kinetin, TDZ, zeatin), GA3, ancymidol, polyamines (putrescine, spermine, spermidine), ACC, AgNO3 and CoCl2 on the amount of direct embryo formation on different leaf locations (the cut end, the adaxial side, the abaxial side and the leaf tip). The results showed that there was a genotypic effect on direct embryo formation induced by cytokinins that 13.32 μM BA and 4.92 μM 2iP was the most effective in P. amabilis and P. Nebula, respectively. Besides, explant position highly affected embryogenic competence of leaf cells in both species that the cut end showed highest embryogenic response, the adaxial side was the second, and then the abaxial side and the leaf tip. Altogether, cytokinins tested were all effective in both species, and ACC at 20 μM had 35% of embryogenic response in P.amabilis. However, auxins, GA3, ancymidol and polyamines were inhibitory in both species.
32 citations