The Physiological Significance of Kinetin‐ and Gibberellin‐like Root Hormones

145

ABSTRACE MATERIALS AND METHODSThe biosynthesis of cytokinins was examined in pea (Pisum sativum L.) plant organs and carrot (Daucus carota L.) root tissues. When pea roots, stems, and leaves were grown separately for three weeks on a culture medium containing 18-"4Cadenine without an exogenous supply of cytokinin and auxin, radioactive cytokinins were synthesized by each of these organs. Incubation of carrot root cambium and noncambium tissues for three days in a liquid culture medium containing 18-'Cladenine without cytokinin demonstrates that radioactive cytokinins were synthesized in the cambium but not in the noncambium tissue preparatioa. The radioactive cytokinins extracted from each of these tissues were analyzed by Sephadex LH-20 columns, reverse phase high pressure liquid chromatography, paper chromatography in various solvent systems, and paper electrophoresis. The main species of cytokinins detectable by these methods are N'4-A2-isopentyl)adenine-5'-monophosphate, 644-hydroxy-3-methyl-2-butenyl-amino)-9-,-ribofuranosylpurine-5'-monophosphate, N'-Q52-isopeatenyl)adenosine, 6-(4-hydroxy-3-methyl-2-butenylamino)-9-ft-ribofuraosylpurine, N'-(A2-isopentenyl)adenine, and 6-(4-hydroxy-3-methyl-2-butenylamino)purine. On the basis of the amounts of cytokinin synthesized per gram fresh tissues, these results indicate that the root is the major site, but not the only site, of cytokinin biosynthesis. Furthermore, cambium and possibly all actively dividing tissues are responsible for the synthesis of this group of plant hormones.There is evidence that cytokinins exist in the roots (15,16) and that cytokinins from xylem exudate may come from the roots (9,17 2Abbreviations: Ade, adenine; Ado, adenosine; i6Ade, N6-(A2-isopentenyl)adenine; i6Ado, N6-(A2-isopentenyl)adenosine; io6Ade, 6-(4-hydroxy-3-methyl-2-butenylamino) purine; io6Ado, 6-(4-hydroxy-3-methyl-2-butenylamino)-9-,-ribofuranosylpurine. imbibed for 16 h with running tap water, and surface-sterilized for 10 min with 0.5% NaOCl. The seeds were thoroughly rinsed with sterile distilled H20, and three seeds were grown on 50 ml of a basic culture medium (8)

Section: Abstrace Materials and Methodsmentioning

confidence: 99%

“…There is evidence that cytokinins exist in the roots (15,16) and that cytokinins from xylem exudate may come from the roots (9,17). This evidence has been reviewed by Torrey (18).…”

mentioning

confidence: 99%

mentioning

confidence: 99%

See 1 more Smart Citation

Localization of Cytokinin Biosynthetic Sites in Pea Plants and Carrot Roots

Chen¹,

Ertl²,

Leisner³

et al. 1985

145

“…Precursor of the purine moiety of cytokinins has been shown to be Ade (3,7). Although there is evidence that cytokinin does exist in the root tip, either free (14) or as constituents of tRNA (1,9,14), and that cytokinins from xylem exudate may come from the roots (11,15), the question of whether the intact root tips and/or other plant parts serve as a primary site of cytokinin biosynthesis remains to be answered.…”

mentioning

confidence: 99%

Cytokinin Biosynthesis in Cultured Rootless Tobacco Plants

Chen

Petschow²

1978

Biosynthesis of cytokinin in shoots was examined by growling rootless tobacco (Nicodans tabacum) plants in vitro. The rootless plants were originated by culturing tobacco callus on a high cytokinin-low auxin medium to induce the formation of plantlets which were then grown on medium without exogenous cytokinin and auxin. The rootless plants supplied with I14Cladenine synthesized ethanol-ethyl acetate-water-soluble radioactive components, portions of which had the same chromatographic and electrophoretic mobilities as N6-(A2-isopentenyl)adenine, N"-(A2-isopentenyl)adenosine, 6-(4-hydroxy-3-methyl-2-butenylamino)purine and 6-(4-hydroxy-3-methyl-2-butenylamino)-9-@-D-ribofuranosylpurine. The total amount of these four major cytokinins was estimated to be present at a concentration of 14 to 23 nanomoles per kilogram of rootless plant. These data indicate that adenine serves as a precursor of the purine moiety of cytokinin molecules and that the cytokinin biosynthetic sites are also located in the shoot in addition to the presumed root sites.i6Ade,2 io6Ade, and closely related derivatives constitute a group of plant hormones, the cytokinins, which promote cell division and differentiation. Precursor of the purine moiety of cytokinins has been shown to be Ade (3, 7). Although there is evidence that cytokinin does exist in the root tip, either free (14) or as constituents of tRNA (1,9,14), and that cytokinins from xylem exudate may come from the roots (11, 15), the question of whether the intact root tips and/or other plant parts serve as a primary site of cytokinin biosynthesis remains to be answered.Information about the biosynthesis of cytokinins in roots comes from indirect evidence based on collection of materials by diffusion and extraction together with the bioassay of substances from root exudates. This evidence has been reviewed recently in some detail by Torrey (17). 2 Abbreviations: Ade: adenine; i6Ade: N6-(A2-isopentenyl)adenine; i6Ado: N6-(A&2-isopenten6yl)adenosine; io6Ade: 6-(4-hydroxy-3-methyl-2-butenylamino)purine; io Ado: 6-(4-hydroxy-3-methyl-2-butenylamino)-9-/?-ribofuranosylpurine. Chromatograms were cut into 1-cm sections and placed in vials containing scintillation fluid (4). Radioactivity was measured in a Nuclear-Chicago Unilux II scintillation system. For liquid samples, an aliquot no more than 0.5 ml was added to 10 ml of Bray's solution (2). Counting efficiency of 14C samples was 74% for paper chromatogram sections and 90%7o for liquid samples.A Cary model 14 spectrophotometer was used to measure the quantity of purine bases and cytokinins.Histology. A modified procedure of Johansen (10) was used in histological examination of the rootless plants. The plants harvested from the culture media were rinsed gently in distilled H20 to remove adherent medium from the stem bases. Stem bases were cut into 1-cm lengths which included any development in the base area except for leaves. The stem bases were dropped immediately into a fixative containing 100 ml of 50%1o ethanol, 50 ml of formalin,...

“…Application of synthetic cytokinins to the bases of unrooted cuttings caused inflorescence growth. Kende and Sitton (15) found that gibberellin application to rootless, etiolated pea seedlings caused longer stems tham rooted, untreated controls. Kinetin, benzyladenine, zeatin, and SD 83395 had no effect on the length of rootless seedlings.…”

mentioning

confidence: 99%

Hormonal Regulation of Cell Elongation in the Hypocotyl of Rootless Soybean: An Evaluation of the Role of DNA Synthesis

Holm

Key

1969

Abstract. A method was developed where soybean seedlings were grown without roots to study the influence of hormones of root origin on shoot growth. Excision of the root resulted in inhibition of apical section growth and DNA synthesis and inhibited elongating section growth. A synthetic cytokinin restored DNA synthesis in the apical seotion, but did not influence growth in either the apical or elongating sections. Low concentrations of gibberellin with the cytokinin restored growth in the apical section. Gibberellin alone was sufficient to restore grow-th in the elongating section.An inhibitor of DNA synthesis, 5-fluorodeoxyuridine, inhibited the increase in apical section DNA without inhibiting control or gibberellin-induced growth in the elongating section. Experiments with 14C-thymidine resulted in no DNA labeling differences in the elongating section under conditions where gibberellin-induced elongation varied from 50 % to 73 % above controls. It was concluded that gibberellin-induced elongation in soybean hypocotyl occurred in the absence of DNA synthesis. Gibberellin does stimulate DNA synthesis in the apical tissue apart from its effect on cell elongation.Excised soybean hypocotyl elongated maximally at 10-8 M auxin. At higher auxin concentrations, fresh weight and ethylene production increased, but elongation was reduced. Addition of GA to the higher auxin concentations resulted in a 50 % inhibition in auxin-induced ethylene production and resumption in maximal elongation. Added ethylene inhibited elongation 30% at 2 A/l. Addition of up to 100 ll/ ethylene did not inhibit elongation with GA present in the incubation medium. Thus GA may counteract ethylene inhibition of cell elongation in addition to inhibiting othylene production in auxin-treated tissues.Thirty years ago Went (31) proposed the existence of-hormones produced by the roots that were necessary for stem growth. Chibnall (2), studying protein loss in detached leaves, suggested that the root system exerted an influence on leaf protein metabolism. He found that development of adventitious roots on the petioles of detached leaves caused a reduction in the rate of protein breakdown (3). Richmond and Lang (26) discovered a chemical basis -for senescence retardation when they showed that kinetin delayed yellowing of detached Xanthium