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Zeatin

About: Zeatin is a(n) research topic. Over the lifetime, 2467 publication(s) have been published within this topic receiving 64092 citation(s). The topic is also known as: Zeatin & (E/Z)-zeatin.


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Journal ArticleDOI
TL;DR: The authors' entry into the polyamine field was accidental, but their attention was drawn to a report that the rapid senescence of detached leaves of this plant could be delayed substantially by the application of arginine, and this work was started on cereal leaf protoplasts.
Abstract: Our entry into the polyamine field was accidental. As plant physiologists interested in the regeneration of entire plants from isolated single cells and protoplasts, we had turned our attention to the two most important groups of food plants, the cereals and the legumes (1, 2). When we began this work about a decade ago, there had been no successful protoplast regeneration of any plants in these groups, although numerous researchers had been successful with various members of the Solanaceae (tobacco, petunia, potato, tomato), as well as a few species in other families (3). Today, several of the Leguminosae have been successfully regen erated from protoplasts (4-6), but only one report of cereal regeneration from protoplasts, in pearl millet, exists in the literature (7). Why should cereal leaf protoplasts behave so diflerently from protoplasts of other species? We had been working with oat, and our attention was drawn to a report that the rapid senescence of detached leaves of this plant could be delayed substantially by the application of arginine (8). It is well known to plant physiologists that leaves detached from the plant initiate a rapid and massive hydrolysis of proteins and nucleic acids, then senesce, yellow, and die. These events can be delayed, and sometimes prevented, by cytokinins, exemplified by N-isopentenyl adenosine or zeatin (9). We had, of course, applied cytokinins to our isolated oat leaf protoplasts, but without positive

498 citations

Journal ArticleDOI
TL;DR: The effects of the increased levels of endogenous cytokinins in non-heat-shocked transgenic plants seemed to be confined to aspects of growth rather than differentiation, since no alterations in the programmed differentiation pattern were found with increased cytokinin levels.
Abstract: Cytokinins, a class of phytohormones, appear to play an important role in the processes of plant development. We genetically engineered the Agrobacterium tumefaciens isopentenyl transferase gene, placing it under control of a heat-inducible promoter (maize hsp70). The chimeric hsp70 isopentenyl transferase gene was transferred to tobacco and Arabidopsis plants. Heat induction of transgenic plants caused the isopentenyl transferase mRNA to accumulate and increased the level of zeatin 52-fold, zeatin riboside 23-fold, and zeatin riboside 5[prime]-monophosphate twofold. At the control temperature zeatin riboside and zeatin riboside 5[prime]-monophosphate in transgenic plants accumulated to levels 3 and 7 times, respectively, over levels in wild-type plants. This uninduced cytokinin increase affected various aspects of development. In tobacco, these effects included release of axillary buds, reduced stem and leaf area, and an underdeveloped root system. In Arabidopsis, reduction of root growth was also found. However, neither tobacco nor Arabidopsis transgenic plants showed any differences relative to wild-type plants in time of flowering. Unexpectedly, heat induction of cytokinins in transgenic plants produced no changes beyond those seen in the uninduced state. The lack of effect from heat-induced increases could be a result of the transient increases in cytokinin levels, direct or indirect induction of negating factor(s), or lack of a corresponding level of competent cellular factors. Overall, the effects of the increased levels of endogenous cytokinins in non-heat-shocked transgenic plants seemed to be confined to aspects of growth rather than differentiation. Since no alterations in the programmed differentiation pattern were found with increased cytokinin levels, this process may be controlled by components other than absolute cytokinin levels.

394 citations

Journal ArticleDOI
TL;DR: It is shown that dark-grown wild-type seedlings exhibit similar phenotypic traits if any one of a variety of cytokinins are present in the growth medium, and a model is proposed in which light and cytokinin act independently or sequentially through common signal transduction intermediates to control the downstream light-regulated responses.
Abstract: When grown in the absence of light, Arabidopsis thaliana deetiolated (det) mutants develop many of the characteristics of light-grown plants, including the development of leaves and chloroplasts, the inhibition of hypocotyl growth elongation, and elevated expression levels of light-regulated genes. We show here that dark-grown wild-type seedlings exhibit similar phenotypic traits if any one of a variety of cytokinins are present in the growth medium. We further show that the striking phenotype of det mutants is unlikely to be caused by different levels of cytokinins in these mutants. The three major Arabidopsis cytokinins, zeatin, zeatin riboside, and isopentenyladenosine, accumulate to similar levels in wild-type seedlings grown in either the light or the dark. There is no consistently different pattern for the levels of these cytokinins in wild-type versus det1 or det2 mutants. However, det1 and det2 have an altered response to cytokinin in a detached leaf senescence assay and in tissue culture experiments. A model is proposed in which light and cytokinins act independently or sequentially through common signal transduction intermediates such as DET1 and DET2 to control the downstream light-regulated responses.

363 citations

Journal ArticleDOI
TL;DR: The auxin/cytokinin ratio in the leaves and roots may explain both the salinity-induced decrease in shoot vigour and the shift in biomass allocation to the roots, in agreement with changes in the activity of the sink-related enzyme cell wall invertase.
Abstract: Following exposure to salinity, the root/shoot ratio is increased (an important adaptive response) due to the rapid inhibition of shoot growth (which limits plant productivity) while root growth is maintained. Both processes may be regulated by changes in plant hormone concentrations. Tomato plants (Solanum lycopersicum L. cv Moneymaker) were cultivated hydroponically for 3 weeks under high salinity (100 mM NaCl) and five major plant hormones (abscisic acid, ABA; the cytokinins zeatin, Z, and zeatin-riboside, ZR; the auxin indole-3-acetic acid, IAA; and the ethylene precursor 1-aminocyclopropane-1-carboxylic acid, ACC) were determined weekly in roots, xylem sap, and leaves. Salinity reduced shoot biomass by 50-60% and photosynthetic area by 20-25% both by decreasing leaf expansion and delaying leaf appearance, while root growth was less affected, thus increasing the root/shoot ratio. ABA and ACC concentrations strongly increased in roots, xylem sap, and leaves after 1 d (ABA) and 15 d (ACC) of salinization. By contrast, cytokinins and IAA were differentially affected in roots and shoots. Salinity dramatically decreased the Z+ZR content of the plant, and induced the conversion of ZR into Z, especially in the roots, which accounted for the relative increase of cytokinins in the roots compared to the leaf. IAA concentration was also strongly decreased in the leaves while it accumulated in the roots. Decreased cytokinin content and its transport from the root to the shoot were probably induced by the basipetal transport of auxin from the shoot to the root. The auxin/cytokinin ratio in the leaves and roots may explain both the salinity-induced decrease in shoot vigour (leaf growth and leaf number) and the shift in biomass allocation to the roots, in agreement with changes in the activity of the sink-related enzyme cell wall invertase.

346 citations

Journal ArticleDOI
TL;DR: Evidence is presented strongly indicating that zeatin does occur naturally in its unsubstituted form and also in nucleoside and nucleotide forms and still a high degree of reproducibility from test to test.
Abstract: Three laboratories previously have obtained from Zea mays kernels (milk stage) one or more 6-(substituted)aminopurines capable of greatly promoting cell division in plant tissue cultures.1-3 At least two of the laboratories have worked on a single compound4 which has been identified as 6-(4-hydroxy-3-methylbut-2-enyl)aminopurine.5 The name zeatin has been applied to this particular compound.6 Only a small portion of the total cell-division activity in crude extracts from kernels seems to be due to zeatin'-3 and its actual existence in the kernel has been questioned.7 We now present evidence strongly indicating that zeatin does occur naturally in its unsubstituted form and also in nucleoside and nucleotide forms. Assay.-The active materials in the maize extracts were detected by using the soybean (Glycine max, var. Acme) tissue test.3' 8 This tissue requires a substance like zeatin for continued cell division and has proved to be very sensitive to zeatin and similar compounds. For example, in recent tests we have obtained measurable growth responses to as little as 5 X 10-11 M zeatin. Most assays were performed with small quantities of extracts which contained rather low concentrations of active materials. With such low concentrations, the soybean test shows considerable variation of fresh weights for individual pieces in a particular assay but still a high degree of reproducibility from test to test. Repeats of all experiments reported here have given consistent results. Stock cultures of the soybean tissue have been maintained on a medium containing (mg/liter): KH2PO4, 300; KNO3, 1000; NH4NO3, 1000; Ca(NO3)2 .4H20, 500; MgSO4-7H20, 71.5; KCl, 65; MnSO4 .4H20, 14; NaFe ethylenediaminetetraacetate, 13.2; ZnSO4 7H20, 3.8; H3BO3, 1.6; Cu(NO3)2.3H20, 0.35; (NH4)6 Mo7024 *4H20, 0.1; i-inositol, 100; nicotinic acid, 0.5; pyridoxine HCI, 0.1; thiamin * HCl, 0.1; a-naphthaleneacetic acid, 2; kinetin, 0.5; sucrose, 30,000; and Bacto-agar, 10,000. The pH was adjusted to 5.8 (NaOH). A preparation to be tested for cell-division activity was added to this medium with the kinetin omitted, the pH was adjusted to 5.8 with NaOH or HCl, and sterilization was achieved by autoclaving. Each of four 125-ml Erlenmeyer flasks containing 50 ml of hardened medium was planted with four pieces of the stock soybean tissue. After growth for 28 days at 27°C and constant fluorescent lighting at about 40 ft-c, the pieces were weighed individually. The fresh weight averages indicate relative amounts of cell division. Extracts.-Frozen kernels (milk stage) of Zea mays, var. Golden Cross Bantam, were extracted by macerating in either cold or boiling 95 per cent ethanol. The final concentration of ethanol was adjusted to 70 per cent (assuming the weight of kernel was due entirely to water). The extract was cooled and the filtered precipitate discarded. The filtrate was used in all of the experiments. Chromatography.-Ethanol solutions or other preparations were streaked on sheets of Whatman #1 filter paper. For development, one of the following mix-

336 citations

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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202135
202034
201932
201848
201753
201651