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.

Complete Release of Axillary Buds from Apical Dominance in Intact, Light-Grown Seedlings of Pisum sativum L. following a Single Application of Cytokinin

Abstract: Single applications of either 6-benzyladenine or zeatin to inhibited axillary buds of intact, light-grown seedlings of Pisum sativum L. cv Black-eyed Susan, resulted in the formation of rapidly elongating, leafy shoots. Similar treatment with kinetin or isopentenyladenine caused only limited but outgrowth which stopped 6 days after application.

Genotypic and media effects on plant regeneration from cotyledon explant cultures of some Brassica species

Abstract: Conditions were established for efficient plant regeneration from cotyledon explant calli in different cultivars ofBrassica juncea, B. campestris andB. carinata on Murashige & Skoog's (MS) medium supplemented with various combinations of cytokinins and auxins. Regeneration frequency, however, varied with genotype and the different growth hormone combinations in media. Almost in all species, MS medium with zeatin (1.0 mg 1-1) and IAA (0.1 mg l-1) was found to be best for shoot organogenesis followed by the ones containing high kinetin (2.0 mg l-1) and low IAA (0.02 or 0.2 mg l-1) concentrations. On these media, the cotyledonary explants invariably underwent callusing followed by multiple shoot formation, which could be separated and subcultured for further propagation. Number of shoots per cotyledon explant cultured varied from 0 to as many as 50. InB. juncea andB. campestris, the regeneration frequency declined sharply in the absence of auxin in medium. BAP in combination with NAA yielded no or a reduced number of shoots. Shoot organogenesis also declined with the reduction in photoperiod from continuous light to 16 hours. Shoots were easily rooted during prolonged incubation on the same medium and whole plants were transferred to pots in the greenhouse and grown to maturity.

The Action of Some Cytokinins on the Rest‐period and the Content of Acid Growth‐inhibiting Substances in Potato

Abstract: Apical sections of resting potato tubers of the variety Majestic, which is known for a long rest-period, were treated for 6 and 24 hours with water or with the cytokinins kinetin or zeatin. The cytokinin-treatment breaks the rest-period very rapidly. The buds begin to sprout already after 2–3 days. The content of acid inhibitors (the β inhibitor) in extracts of the peelings from cytokinin-treated sections in much lower than in similar extracts from water-treated, resting sections. Already 6 hours after the beginning of the treatment, differences in inhibitor content can be demonstrated.

Cytokinins in Xanthium strumarium L.: Distribution in the Plant and Production in the Root System

Abstract: Cytokinins from leaf laminae, buds, petioles, stems, roots, and root exudate of mature vege tative plants of Xanthium strumarium L. were extracted, fractionated, and partially character ized by means of column chromatography with Sephadex LH20. Two peaks of cytokinin activity with elution volumes corresponding to zeatin and zeatin riboside were detected, in varying concentrations, in all plant parts. A third cytokinin, detected only in petioles and in expanding and mature leaves, eluted off the Sephadex column before zeatin riboside. This cytokinin (peak 'a') was converted to zeatin or to a zeatin-like cytokinin following both acid hydrolysis and treatment with /3-glucosida.se. Peak 'a' was not detected in buds or in the young est developing leaves but was the predominant cytokinin present in half-expanded and more mature leaves. By contrast, the zeatin riboside-like peak (peak 'b') constituted the major cyto kinin in root exudate, apical buds, and the youngest developing leaves, while not greatly contributing to the cytokinin content of mature leaves. The detopped root system was shown to be capable of cytokinin production. The distri bution of cytokinins in the plant is discussed in relation to their probable origin in the root system. INTRODUCTION Cytokinins have been detected in a wide variety of plant tissues and several com pounds with cytokinin activity have now been fully characterized (e.g. Letham, Shannon, and McDonald, 1964; Koshimizu, Kusaki, and Mitsui, 1967 ; Dyson and Hall, 1972; Horgan, Hewett, Purse, and Wareing, 1973; Letham, 1973). However, there have been few investigations into the distribution of the different endogenous cytokinins within a single plant. Such information would be of considerable value with regard to a number of problems concerning the synthesis, movement, and role of these substances as regulators of plant growth and development. Previous studies comparing levels of cytokinins in various plant parts have indi cated fruits to be a major source of cytokinins while vegetative tissues contain much lower levels (e.g. Miller and Witham, 1964; Krasnuk, Witham, and Tegley, 1972). Consequently much work on cytokinin characterization has been concentrated on fruits. Nevertheless, vegetative tissues have not been entirely neglected and several reports have brought to light the existence of qualitative as well as quantitative 1 Present address : Department of Botany, University of Glasgow. This content downloaded from 157.55.39.116 on Sat, 11 Jun 2016 05:54:28 UTC All use subject to http://about.jstor.org/terms Henson and Wareing—Cytokinins in Xanthium 1269 differences in the content of cytokinins between, for example, leaves and xylem sap (Klâmbt, 1968; Hewett, 1973), roots and xylem sap (Yoshida, Oritani, andNishi, 1971 ; Yoshida and Oritani, 1972), and leaves and buds (Engelbrecht, 1971 ; Hewett, 1973; Hewett and Wareing, 1973a, b). The present paper is concerned mainly with a qualitative analysis of cytokinins and their distribution and site of production in mature vegetative plants of Xanthium, strumarium L., a species in which cytokinin levels are greatly influenced by photo period (Van Staden and Wareing, 1972). MATERIALS AND METHODS Plant material Plants of Xanthium strumarium were raised from seed and grown in a heated glasshouse under 18 h days as described previously (Henson and Wareing, 1974). Material for cytokinin extrac tion was harvested when the plants had developed 12 to 16 leaves. Root exudate (root pres sure sap) was obtained by detopping plants above the cotyledonary node. The exuding sap was collected over 24 h and frozen (—15 °C) prior to analysis. For purposes of identification leaves were numbered basipetally according to the procedure of Salisbury (1955) with leaf No. 1 being the first leaf with a midrib 1 -0 cm or more long. Extraction and partial purification of cytokinins Tissues were initially extracted, twice in 80% (v/v) aqueous methanol, using 10 ml g_1 fr. wt. The combined methanolic extracts were purified to give an n-butanol-soluble fraction by either of two methods, both of which gave very similar results. Method A involved reducing the methanolic solution to a small volume on a rotary film evaporator at 30 °C. The extract was then frozen, thawed, and centrifuged (20 000 g for 30 min) to remove chlorophyll, partitioned at pH 2-5 against ethyl acetate (three times), and then at pH 8-0 against water-saturated n-butanol (four times). The w-butanol fraction was then subject to paper or column chromatography using Sephadex LH20 prior to analysis for cytokinins. Cytokinin activity due to ribonucleotides was also estimated following incubation of the aqueous phase remaining after partitioning with the enzyme alkaline phosphatase (Sigma, from calf intestinal mucosa). The treated extract was then repartitioned against ra-butanol (Miller, 1965). Most such extracts yielded little activity and hence the results are presented only for the non-nucleotide cytokinins. With method B the methanolic extract was passed directly through a column of cation exchange resin (Zerolit 225, SRC 14, H+ form) at pH 2-5. After washing the column to remove anions and neutral substances (with two column volumes of 80% methanol and 10 column volumes of distilled water), the cations were eluted with two column volumes of 2 N NH4OH followed by 10 columns of 5 N NH4OH. The eluate was reduced to dryness and the residue redissolved in water and partitioned at pH 8-0 against water-saturated n-butanol (four times). The n-butanol fraction was then further purified as described above for method A. Paper chromatography was conducted using Whatman 3 MM paper and isopropanol: ammonia (0-88 s.g.) iwater (10:1:1, by vol.) as the developing solvent. Column chromatography on Sephadex LH20 (Armstrong, Burrows, Evans, and Skoog, 1969) was conducted using a 2-5 cm x 90-0 cm column eluted with 35% (v/v) aqueous ethanol at a flow rate of either 20 or 30 ml h-1. Bioassay Cytokinin activity was detected using the soybean callus bioassay of Miller (1968), with modifications as previously described (Henson and Wareing, 1974). RESULTS General distribution of cytokinins in the plant The distribution of cytokinins present in purified extracts of roots, root exudate, stems, petioles, leaf laminae, and axillary buds following fractionation on the This content downloaded from 157.55.39.116 on Sat, 11 Jun 2016 05:54:28 UTC All use subject to http://about.jstor.org/terms 1270 Henson and Wareing—Cytokinins in Xanthium