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Abstract

A technique is described for forcing the buds of tea crabapple using cytokinins. Of the cytokinins tested, 6-benzylamino purine (BA) produced the best results at 2,000 ppm, 6-(benzylamino)-9-(2-tetrahydropyranyl)-9H-purine (PBA) was nearly as effective, and N6-[Δ2-isopentenyl]-adenosine (IPA) and N6-[Δ2 isopentenyl]-adenine (2ip) were ineffective. Depending on the cytokinin used, inclusion of 0.5 or 1.0% surfactant was required to insure consistent results. No differences were found among 8 surfactants tested. Dimethylsulfoxide (DMSO) was an excellent solvent for the cytokinins and slightly enhanced their effect. The treatment effect was not translocated from the site of application. This method was consistent, faster than 10 weeks of cold treatment, less phytotoxic than cytokinins applied in a lanolin fraction, and permitted rapid spray application of small quantities of solution.

Open Access

Abstract

Two natural cytokinins, zeatin and dihydrozeatin, were effective in preserving broccoli appearance and chlorophyll content. Single treatments with 100 ppm aqueous solutions of the 2 compounds, followed by storage at 13°C, permitted storage life of 5 days for zeatin- and 4 days for dihydrozeatin-treated samples of broccoli. Repeated treatments with these compounds increased broccoli storage life to 6 days at 13°C, approaching the apparently limiting value of 7 days conferred by the synthetic cytokinin, 6-benzylamino purine (25 ppm). Broccoli without cytokinin treatment remained salable for only 2 days at 13°C. Visual scores for color were linearly related to chlorophyll concentration.

Open Access

Conditions for improving the efficiency of shoot regeneration from leaf sections of highbush blueberry (Vaccinium corymbosum L.) were investigated. Effectiveness of tissue culture medium supplemented with the cytokinin conjugate zeatin riboside or the cytokinin zeatin at 10, 20, or 30 μm was compared with medium supplemented with the optimum 2iP concentration of 15 μm. Use of 20 μm zeatin riboside resulted in the most shoots per leaf section, » 6-fold higher than the number of shoots produced on 2iP medium. The number of shoots produced on medium supplemented with zeatin was not significantly higher than the number of shoots produced on 2iP medium. Consequently, we concluded that the cytokinin conjugate zeatin riboside was more effective than either of the free cytokinins, 2iP or zeatin, in promoting shoot regeneration from leaf sections of highbush blueberry. Chemical names used: 6-(y,y-dimethylallylamino)-purine (2iP); 6-(4-hydroxy-3-methyl-but-2-enylamino)purine (zeatin).

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Abstract

Xylem sap from three apple (Malus domestica Borkh.) rootstocks was vacuum-extracted during and after artificial chilling and during forcing of chilled and unchilled trees. Sap was assayed for cytokinins by immunoassay and for soluble carbohydrates (sorbitol, glucose, fructose, and sucrose) by enzymatic assays. Xylem cytokinin increased after 10 days of forcing at 21/18C regardless of chilling treatment. Cytokinin levels decreased significantly as budbreak occurred in fully chilled trees, but not in unchilled trees with very little budbreak. Xylem sucrose, glucose, and fructose concentrations decreased upon exposure to 21/18C, then increased after 30 days in both chilled and unchilled trees. Sorbitol level remained low and unchanged throughout growth. Full chilling was not necessary in apple for adequate cytokinin and carbohydrates to be transported to the developing buds via the xylem stream. Sorbitol apparently is not used in carbohydrate transport from reserve, as it is in photosynthesis.

Open Access

Abstract

The application of cytokinins and gibberellins alone and in combination to ‘Delicious’ apples just after full bloom affected fruit shape by increasing the length-to-diameter ratio of the fruits. Cytokinins caused fruits to be longer with prominent well-developed calyx lobes. The treated fruit had the appearance of fruits grown where early season temperatures are cool. Gibberellin A4 + A7 caused fruits to be longer but did not appreciably affect the development of the calyx lobes.

Open Access

Tissue proliferation (TP) is characterized primarily by the formation of galls or tumors at the crown of container-grown rhododendrons propagated in vitro. However, TP of Rhododendron `Montego' is observed initially in in vitro shoot cultures and it is characterized by the formation of multiple shoots with small leaves and nodal tumors. The formation of shoots in `Montego' TP (TP+) shoot cultures occurs without the presence of exogenous cytokinin in the medium, unlike normal `Montego' (TP–) shoot cultures, which require cytokinin for shoot growth. Structural studies have shown that tumors are composed of many adventitious buds and parenchyma cells, suggesting that TP is a result of abnormal cytokinin regulation that is controlling tumor and shoot formation. Two approaches are being used to determine if differences in cytokinin concentration and/or metabolism exist between TP+ and TP– shoot cultures. In the first approach, shoot cultures are grown in vitro for 1 week in the presence of tritiated isopentenyladenine (iP). Cytokinin uptake and metabolism are analyzed using HPLC and other analytical methods. Experiments suggest that extensive degradation and N-glucoside conjugation occur in TP+ and TP– shoots, resulting in the removal of most of the exogenous iP. In the second approach, the levels of endogenous cytokinins such as iP, isopentenyladenosine, zeatin, and zeatin riboside, are being measured in TP+ tumors and shoots and in TP– shoots by an ELISA method.

Free access

given in Vlachou et al. (2016b) . The cultures were maintained with a number of subcultures on the initiation medium followed by one subculture on Hf-MS medium. Effect of cytokinin type and concentration on shoot multiplication Adult plant- or seedling

Free access

Similarities exist between the effects of phytochrome and cytokinins on plant growth and development (e.g., chloroplast development, amaranthin synthesis, seed germination). It is unclear, however, if and how these two systems interact. The coaction between phytochrome and cytokinins was investigated by using Nicotiana plumbaginifolia plants transformed with the isopentenyl transferase (ipt) cytokinin gene and treated with end-of-day (EOD) red (R) and far-red (FR) light. The ipt gene was under control of either a constitutive cauliflower mosaic virus promoter (35S-plants) or an inducible, heat shock promoter (HS-plants). When treated with EOD FR light, whole plants were characterized by decreased chlorophyll concentrations and increased fresh weights. When treated with EOD R light, 35S-plants contained high concentrations of zeatin riboside (ZR) compared to plants treated with EOD FR light. When treated with EOD FR light, HS-plants contained high concentrations of ZR compared to plants treated with EOD R light. Both cytokinin responses were photoreversible. The reasons for the differences between the 35S- and HS-plant responses are not known. Results appear to implicate interactions between phytochrome and cytokinins in plant growth and development.

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Abstract

Plant growth regulator studies and plant tissue culture research have been closely related and mutually supportive. The manipulation of plant cells, tissues, and organs in culture, with important applications in propagation and genetic modification of plants, is highly dependent on the use of appropriate growth regulator regimes. Conversely, tissue culture systems are useful as bioassays to define the growth-regulating activity of many compounds. The discovery of the cytokinin N-(2-furanylmethyl)-1H-purin-6-amine (kinetin) by Miller et al. (17) was particularly relevant in this respect. Whereas the testing of this cytokinin and its structural analogues for biological activity was dependent on callus culture bioassays, the subsequent availability of synthetic cytokinins created many new opportunities in the field of plant tissue culture.

Open Access
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Abstract

The conversion of genetically staminate plants of Vitis to functional hermaphrodites by the application of a cytokinin was successfully accomplished in 8 of 15 clones, including 4 Vitis species and an interspecific hybrid. The time of cytokinin application in relation to the stage of development of the inflorescence was a critical factor in successful conversion. Treated flowers were transformed morphologically as well as functionally, producing typical pistils with stigmas.

The general response of species of Vitis to cytokinin-induced sex conversion and the occasional occurrence of sex conversion in nature lend support to common physiological and genetic bases of sex expression within the genus. A physiological model is proposed in which sex expression is dependent upon the levels of female and male sex inhibitors.

Open Access