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KINETIN-LIKE GROWTH-PROMOTING ACTIVITY OF 1-SUBSTITUTED ADENINES [1-BENZYL-6-AMINOPURINE AND 1-(γ,γ-DIMETHYLALLYL)-6-AMINOPURINE]

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... Three crystalline fractions with cytokinin activity as monitored in the tobacco bioassay were obtained (8,10). The most active fraction was identified as 6(3methyl-2-butenylamino)purine (i6Ade) (6), known at that time only as a synthetic, highly active cytokinin (5,9). The second fraction contained nicotinamide. ...
... 4Present address: Merck Sharp and Dohme Research Laboratories, Rahway, New Jersey 07065. 5 A culture of Corynebacteriwn fascians was kindly given to us in 1964 by Professor K. V. Thimann. lamino)purine (cis-zeatin, c-io6Ade) (21). ...
Article
In addition to the four cytokinins, 6-(3-methyl-2-butenylamino)purine, 6-methylaminopurine and the cis and trans isomers of 6-(4-hydroxy-3-methyl-2-butenylamino)purine, reported earlier from our laboratories, three cytokinin-active fractions have been obtained from the aqueous medium of 6-day-old Corynebacterium fascians cultures. One of these has been identified as 6-(4-hydroxy-3-methyl-cis-2-butenylamino)-2-methylthiopurine (2-methylthio-cis-zeatin, c-ms²io⁶ Ade). The elution volumes of the other two fractions correspond to those of authentic 6-(4-hydroxy-3-methyl-2-butenylamino)-9-β-d-ribofuranosyl-purine and 6-(3-methyl-2-butenylamino)-9-β-d-ribofuranosylpurine, indicating the presence of trace amounts of these two ribonucleosides.
... Cytokinins such as kinetin and BAP are known to delay senescence by preventing degradation of chlorophyll and photosynthetic proteins, and are more effective than zeatin and 2ip (N 6 -2-Isopentenyladenine) in this regard (Hamzi & Skoog, 1964;Yamada et al., 1964;Tetley & Thimann, 1974;Badenoch-Jones et al., 1996). Injured and senescing plants are more susceptible to pathogen attack (Conn et al., 1990;Barna & Gyorgyi, 1992) and therefore, exogenous application of CKs may aid in the delay and reduction of disease. ...
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Blackleg and blackspot are economically important diseases of canola caused by Leptosphaeria maculans and Alternaria brassicae, respectively, and can lead to significant crop losses. In this study, we investigated the effects of cytokinins on the symptoms caused by these two pathogens. We observed that cytokinin, especially 6-benzyl amino purine, was able to significantly reduce disease symptoms and mycelial growth within plant tissues. This cytokinin was also able to inhibit the in vitro growth of both fungi. Other cytokinins such as kinetin or adenine hemisulfate were unable to inhibit fungal growth in vitro, suggesting that the presence of a benzene ring structure is required for the inhibitory effects observed. Our findings are discussed within the context of plant–pathogen interactions.
... Subsequently, iPR was also found in plant soluble RNA (Hall and others 1967;Letham and Ralph 1967). This nucleoside and the corresponding base (iP) were already known to be highly active CKs (Hamzi and Skoog 1964;Hall and others 1966; see also Skoog 1994).The presence of CK moieties in certain tRNAs evoked speculation that the biological action of CKs might possibly be the result of CKs serving as precursors of the modified substituent of some tRNAs. Indications that a fraction of radioactivity derived from exogenously applied [ 14 C] BA to tobacco cultures was found in soluble RNA, principally tRNA, (Fox 1965) supported such suggestions. ...
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Existence of compound(s) inducing cell division in excised plant tissues was spotted more than 100 years ago. Since then research of cytokinins (CKs), plant hormones which in cooperation with other phytohormones, namely auxin, control cytokinesis, and a number of other physiological processes in plants, has advanced correspondingly to the progress in other fields of life sciences. This historical overview is focused on major topics of CK research including (1) discovery of CKs, (2) search for natural CKs, (3) role of CKs in transfer RNA, (4) biosynthesis (5) metabolism, (6) signaling of CKs, and (7) molecular probing of the physiological functions of CKs. Some parts of these subjects can already be assessed within the context of an appropriate time span necessary for critical evaluation. I have used this opportunity to present also some personal recollections, namely those of Prof Folke Skoog, in whose laboratory the first CK, kinetin, was discovered.
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Obwohl seit vielen Jahren größte Zweifel am natürlichen Vorkommen der von KÖGL isolierten Auxine: Auxin a und Auxin b bestehen, scheint die Erwähnung dieser Verbindungen in der Literatur nicht mehr auszumerzen zu sein, was wohl zum Teil darauf zurückzuführen ist, daß die Nacharbeitungen der Köglschen Ansätze mit negativem Ergebnis eben nicht völlig stichhaltig sind. Es ist daher äußerst verdienstvoll, daß jetzt Vliegenhart u. Vliegenhart in Kögls ehemaligem Labor in der Rijksuniversiteit, Utrecht, die dort hinterlegten authentischen Proben der obigen Auxine aus den Jahren 1930–1940 mit Hilfe modernster physikalischer Methoden nachuntersucht haben. Massenspektren und Röntgendiagramme der Substanzen zeigten, daß die Proben von Auxin a mit Cholsäure, von Auxin b mit Thiosemicarbacid und von Auxin a-Lacton mit Hydrochinon identisch sind. Es ist ausgeschlossen, daß die Substanzen erst später vertauscht wurden, da z. B. das von KÖGL publizierte UV-Spektrum von ”Auxin a-Lacton„ dem von Hydrochinon genau gleicht. Keine der untersuchten Proben hatte die Zusammensetzung, die ursprünglich angenommen worden war. Auf Grund dieser Befunde müssen diese Auxine endgültig als nicht existent betrachtet werden. Unterstützt wird dieses Ergebnis noch dadurch, daß es Matsui u. Hwang erstmals gelang, ein Auxin dieser Reihe (Auxin b-Lacton) chemisch zu synthetisieren, und daß das racemische Produkt in verschiedenen Streckungswachstums- und Krümmungs-Tests praktisch keine biologische Aktivität zeigte (Nakamura, Takahashi, Matsui u. Hwang).
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Literature concerning the influences of auxins, adenine, kinetin, light, heat, time, age, and physical characteristics of the medium onin vitro organ formation by sterile seed-plant fragments is reviewed and integrated.
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Benz(a)anthracene induced vegetative buds on callus derived from stem tissue of haploid plants of Nicotiana tabacum a response similar to that obtained by a combination of kinetin and IAA.
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This paper examines the process of research collaboration with other scientists based solely upon the experiences of the author: initiation of cooperation; agreement on purpose and responsibility; development of the joint project; information exchange and writing; and consequences unique to each research project.
N,N'-Diphenylurea was shown to have reproducible cytokinin activity. Some 500 ureas, mainly of the N-monosubstituted and N,N'-disubstituted types, were tested and about one half of these were active. Attempts were made to correlate chemical structure with biological activity. Although there are some exceptions to nearly every generalization it has been possible to formulate some principles. (1) Phenyl urea was the simplest active compound. (2) An HNCONH bridge conferred higher activity than an HNCSNH linkage and any other tested arrangement of the bridge gave inactive compounds. (3) Compounds in which both amino hydrogen atoms on one or both sides of the bridge were substituted were of low activity or were inactive. (4) Many compounds of the type RNHCONH2 in which R = a substituted phenyl ring were tested. Ring substitution generally increased the activity and the highest activity was associated with meta substitution and the lowest with ortho. Compounds with electron-attracting substituents were generally more active than those with electron-donating substituents. Pyridyl compounds were active but compounds with non-planar rings were inactive. (5) In compounds of the type RNHCONHR' in which R and R' were phenyl or substituted phenyl groups the highest activities were usually found in compounds with one unsubstituted phenyl ring. Those with two substituted phenyl groups generally had lower activity. Some ureas showed detectable activity at 0\cdot 1 parts/106. This was about four times less active than kinetin when tested in the tobacco pith assay.
Article
This chapter focuses on the group of plant hormones called cytokinins, which are defined as compounds that induce cell division in plant cells in cooperation with an auxin. Gibberellins move in plants in a nonpolar fashion, whereas the cytokinins have been reported to move like auxins in a basipetal polar fashion. Cytokinins are extensively metabolized by plant tissues should be kept in mind in studying their transport. In connection with the movement of cytokinins in plants, it is important to note that cytokinins are also transported through the xylem in intact plants, as cytokinin-like compounds have been detected in the sap of several plants. Adenine derivatives with substituents at positions 2, 7, and 9 are inactive, whereas 1-benzyladenine and 1-(3,3-dimethylallyl) adenine showed cytokinin activity, and 3-(3,3-dimethylallyl)adenine (triacanthine), which occurs naturally in plants, showed cytokinin activity only after its conversion, through autoclaving, to the 6-isomer. The chapter discusses the biological effects of cytokinins, metabolism and intracelldar localization of cytokinins in plants, mechanism of action of cytokinins, and metabolic effects of cytokinins.
Article
Higher plants generate active substances, termed phytohormones, having the character of tissue hormones. Some of these compounds have been isolated and identified, namely ethylene, heteroauxins, and gibberellic acids. Cell-elongation inhibitors have been detected, but not yet isolated or identified. Natural and synthetic substances with hormone-analogous effects and those with a hormone-antagonistic effect have become known; evidently, they act on the hormonal system of plants which regulates growth, differentiation, and development and can serve as model substances for as yet unknown phytohormones. Certain physiological phenomena suggest the existence of additional phytohormones.
Article
By the synthesis of representative Nx,Ny-dibenzyladenines and determination of their ultraviolet absorption spectra in acidic, basic and neutral solution we have assembled a body of spectral characteristics which makes it possible to distinguish among possible N,N-disubstituted adenines.
Article
Transfer RNA from yeast, liver, and Escherichia coli has cytokinin activity in the tobacco callus bioassay, whereas ribosomal RNA from yeast is inactive. In contrast to fractions of yeast transfer RNA rich in serine acceptor and cytokinin activity, preparations (70 to 90 percent pure) of arginine transfer RNA2, glycine transfer RNA, phenylalanine transfer RNA, and valine transfer RNA1 and of highly purified alanine transfer RNA from yeast were inactive at concentrations of 20 to 2500 micrograms per liter. One molecule of 6-(γ,γ-dimethylallylamino) purine per 20 molecules of yeast tRNA would account for the observed cytokinin activity. The number of major molecular species contributing to cytokinin activity of transfer RNA, therefore, must be small.
Article
N2-(Δ2-isopentenyl) adenosine (IPA) I occurs in the s-RNA of yeast, mammalian, and plant tissue. Its hydroxylated derivative N6-(-4-hydroxy-3-methylbut-2-enyl) adenosine, IV, occurs in the s-RNA of plant tissue. The corresponding isomer, known as ribosyl zeatin, V, also occurs in plant tissue in an unbound form. Compound IV exhibits cytokinin activity in the tobacco pith tissue culture assay and the chlorophyll retention test, but is considerably less active than zeatin in both tests.Acid hydrolysis of samples of s-RNA containing IPA yields two degradation products of IPA, N6-(3-hydroxy-3-methylbutyl) adenine, II, which is a potent cytokinin and 3-H-7, 7-dimethyl-7,8,9-trihydropyrimido-[2,1-i] purine, III, which is not biologically active.
Article
The clarification of the following 2 questions was attempted: (a) are cytokinins precursors in the formation of sRNA, (b) is the observed incorporation of cytokinins into sRNA related to the action of the hormone? Although Escherichia coli contains cytokinins in its sRNA, no cytokinin auxotroph mutants of E. coli could be found and the statistical probability for the existence of such mutants is extremely low. This suggests that cytokinins are not precursors in the synthesis of sRNA. A radioactive cytokinin, 6-benzylamino-9-methyl-purine was synthesized and it was tested whether or not it is incorporated into sRNA of soybean callus tissue. Masking the 9-position of the purine inhibited the incorporation of this cytokinin into RNA while not affecting its biological activity. This is taken as an indication that the observed incorporation of cytokinins such as benzyladenine into sRNA is not related to the action of this hormone.
Article
The cytokinin, N6-(Δ2-isopentenyl) adenosine occurs in the soluble RNA of yeast and mammalian tissue and has now been detected in plant soluble RNA. A hydroxylated derivative of this cytokinin 6-(cis-4-hydroxy-3-methylbut-2-enylamino)-9-,β-D-ribofuranosylpurine has also been identified as a constituent of plant soluble RNA.
Article
When the detached first leaves of green or etiolated oat (Avena sativa cv. Victory) seedlings senesce in the dark, their oxygen consumption shows a large increase, beginning after 24 hours and reaching a peak of up to 2.5 times the initial rate by the 3rd day. This effect takes place while the chlorophyll of green leaves, or the carotenoid of etiolated leaves, is steadily decreasing. Kinetin, at a concentration which inhibits the decrease in pigment, completely prevents the respiratory rise; instead, the oxygen consumption drifts downwards. Lower kinetin concentrations have a proportional effect, 50% reduction of respiration being given by about 0.1 mg/l. About one-fifth of the respiratory rise may be attributed to the free amino acids which are liberated during senescence; several amino acids are shown to cause increases of almost 50% in the oxygen consumption when supplied at the concentrations of total amino acid present during senescence. A smaller part of the rise may also be due to soluble sugars liberated during senescence, largely coming from the hydrolysis of a presumptive fructosan. The remainder, and the largest part, of the increase is ascribed to a natural uncoupling of respiration from phosphorylation. This is deduced from the fact that dinitrophenol causes a similar large rise in the oxygen consumption of the fresh leaves or of leaf segments kept green with kinetin, but causes only a very small rise when the oxygen consumption is near its peak in senescent controls. The respiration of these leaves is resistant to cyanide, and 10 mm KCN even increases it by some 30%; in contrast, etiolated leaves of the same age, which undergo a similar rise in oxygen consumption over the same time period, show normal sensitivity to cyanide. The respiratory quotient during senescence goes down as low as 0.7, both with and without kinetin, though it is somewhat increased by supplying sugars or amino acids; glucose or alanine at 0.3 m bring it up to 1.0 and 0.87, respectively.N(6)-Benzylaminopurine and Delta-2-isopentenylaminopurine act similarly to kinetin in repressing the respiratory rise, the former being five times as active as kinetin, while the latter has only 1% of the activity of kinetin. Zeatin also powerfully prevents senescence. Because the repression of the respiratory rise is shown by each cytokinin at the concentration at which it inhibits senescence, the action is ascribed in both cases to the maintenance of a tight coupling between respiration and phosphorylation. It is pointed out that such an effect would explain many features of cytokinin action.A change in the methodology of the senescence experiments is described and compared with the method previously used, and the influence of temperature and age of the plants on the course of leaf senescence are presented in detail.
Article
In addition to the four cytokinins, 6-(3-methyl-2-butenylamino)purine, 6-methylaminopurine and the cis and trans isomers of 6-(4-hydroxy-3-methyl-2-butenylamino)purine, reported earlier from our laboratories, three cytokinin-active fractions have been obtained from the aqueous medium of 6-day-old Corynebacterium fascians cultures. One of these has been identified as 6-(4-hydroxy-3-methyl-cis-2-butenylamino)-2-methylthiopurine (2-methylthio-cis-zeatin, c-ms(2)io(6) Ade).The elution volumes of the other two fractions correspond to those of authentic 6-(4-hydroxy-3-methyl-2-butenylamino)-9-beta-d-ribofuranosyl-purine and 6-(3-methyl-2-butenylamino)-9-beta-d-ribofuranosylpurine, indicating the presence of trace amounts of these two ribonucleosides.
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The effects of differing cytokinin and auxin concentrations on resistance of tobacco (Nicotiana tabacum L.) tissue cultures to race 0 of Phytophthora parasitica var. nicotianae were examined. With 1 micromolar kinetin and either 11.5 micromolar indoleacetic acid or 1 micromolar 2,4-dichlorophen-oxyacetic acid, tissues from resistant cultivars exhibited a "hypersensitive" reaction to zoospores of the fungus and subsequently were colonized only slightly. With susceptible cultivars or with tissues from resistant cultivars supplied with higher cytokinin levels (e.g. 10 micromolar kinetin), this hypersensitive reaction did not occur and tissues were heavily colonized. Benzylaminopurine and kinetin were particularly effective in eliminating both the hypersensitive reaction and disease resistance. Zeatin and 6-(3-methyl-2-butenylamino)purine were less effective. Increases in indoleacetic acid levels reversed the effects of high cytokinin concentrations. The balance of phytohormones apparently controls the host response to the fungus; thus, in this system, resistance or susceptibility can be studied without changing either host or fungal genotype.
Article
The carrot-root tissue culture assay for cytokinin activity has been improved by changing the site of explant excision and eliminating certain vitamins from the basal medium. These modifications increased its sensitivity and enabled zeatin [6-(4-hydroxy-3-methylbut-trans-2-enyl)aminopurine] to be detected at concentrations less than 5×10-5μM. In the improved assay, zeatin was markedly more active than kinetin, 6-benzylaminopurine, 6-(o-methylbenzyl)aminopurine and 6-(3-methylbut-2-enyl)aminopurine. The activity of zeatin also exceeded that of kinetin in the etiolated bean-leaf disk expansion assay. Zeatin was markedly more effective than kinetin and 6-(3-methylbut-2-enyl)aminopurine in promoting frond expansion and increasing frond number of Spirodela oligorrhiza cultures grown under continuous illumination. Zeatin was also more active than kinetin and 6-(3-methylbut-2-enyl)aminopurine in increasing frond number of Spirodela cultures grown in darkness. In retarding the senescence of disks of leaves of several species, kinetin was considerably more effective than zeatin which was more active than 6-(3-methylbut-2-enyl)aminopurine. The allylic hydroxyl group in zeatin is therefore a structural feature associated with high cytokinin activity. The relative activities of cytokinins can be very different and even in reverse order in different bioassays. It is suggested that this is due to the mechanism of cytokinin action varying in the different biological systems used.
Article
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Two cytokinin ribonucleosides were isolated from an enzymatic hydrolysate of crude Staphylococcus epidermidis tRNA and identified by ultraviolet and mass spectrometry as 6-(3-methyl-2-butenylamino)-9-β-d-ribofuranosylpurine and 6-(3-methyl-2-butenylamino)-2-methylthio-9-β-d-ribofuranosylpurine, respectively. The distribution of cytokinin activity in four tRNAser species from S. epidermidis was also examined. One species, corresponding to the codon UCU, was associated with a peak of cytokinin activity; the other three tRNAser species were inactive.
Article
Höhere Pflanzen erzeugen Wirkstoffe, die den Charakter von Gewebshormonen besitzen. Sie werden als Phytohormone bezeichnet. Einige davon sind isoliert und identifiziert worden: Äthylen, Heteroauxine, Gibberellinsäuren. Zellstreckungshemmstoffe wurden nachgewiesen, jedoch bisher nicht isoliert oder identifiziert. Natürliche und synthetische Stoffe mit hormonanalogen Wirkungen, auch solche mit hormonantagonistischer Wirkung, sind bekannt geworden; sie greifen offenbar in das hormonale System der Pflanzen ein, das Wachstum, Differenzierung und Entwicklung reguliert, und dürfen als Modellsubstanzen für bisher noch unbekannte Phytohormone gelten. Einige physiologische Erscheinungen lassen weitere Phytohormone vermuten.
Article
(R)-(+)- and (S)-(−)-dihydrozeatins [(R)-(+)- and (S)-(−)-6-(4-hydroxy-3-methylbutylamino)purines, 1a and 1b] and their ribosides {(−)-6-[(R)-4-hydroxy-3-methylbutylamino]- and (−)-6-[(S)-4-hydroxy-3-methyl-butylamino]-9-β-D-ribofuranosylpurines, 3a and 3b} were synthesized and tested for their cytokinin activity by four bioassay systems, the growth of tobacco callus, the seed germination of lettuce, the fr. wt increase of excised radish cotyledons and the retardation of chlorophyll degradation in radish cotyledons. In tobacco callus bioassay, 1a was more active than 1b. The ribosides 3a and 3b were not less active than their corresponding aglycones 1a and 1b. In other bioassays used the activity followed the order: 1a >3a >1b >3b. In tobacco callus bioassay and lettuce seed germination, trans-zeatin [6-(4-hydroxy-3-methylbut-trans-2-enylamino)purine] showed stronger cytokinin activity than 1a.
Chapter
Publisher Summary Alkaloids bearing a purine nucleus form a small but important group of natural products. They are often not classified as alkaloids because of their almost universal distribution in living matter and their mode of biosynthesis which shows no relationship to amino acids from which most alkaloids arise. The chapter explores that some purine alkaloids are major constituents of plants such as tea and coffee which are used throughout the world as stimulating beverages. Many of the physiologically important purine alkaloids possess a xanthine nucleus. Xanthine itself has not been found naturally, but several simple N-alkyl derivatives of xanthine are of considerable significance. Prime among these are 1, 3, 7-trimethyIxanthine (caffeine), 1, 3-dimethylxanthine (theophylline), and 3, 7-dimethylxanthine (theobromine). Other purine alkaloids are derivatives of adenine and guanine, with some of the N 6 -alkylated adenines possessing considerable cytokinin-like activity. The cytokinins are plant growth substances which promote cell division.
Article
Callus induction in the rice plant, Oryza sativa L. var. Kyoto Asahi was tested by using completely synthetic media. Callus induction depends on the 2, 4-dichlorophenoxyacetic acid (2, 4-D) concentration only, and kinetin is not absolutely essential for callus induction. Callus was also formed on the medium including 2, 4-D and an adenine derivative 1-ethoxy-9-ethyladenine hydroiodide (Y-96). Shikimic acid had no affect on callus induction. The same concentration of indole-3-acetic acid (IAA) as that of 2, 4-D did not induce callus but at 100ppm callus induction occurred. Chromosomal aberration was observed in callus induced from roots and nodes of shoots. Frequency of aneuploid cells was 80% and 57% in calluses from roots and nodes respectively.
Article
Dans des conditions naturelles, sans stimulation, des explantats circulaires de feuille de Begonia rex Putz, présentent une nette polarité de néoformation de bourgeons. Ce phénomène peut être lié à l'accumulation de substances telles que des cytokinines à la face proximale des sections nervaires. Si, en effet, on traite ces explantats par trempage, dans des solutions aqueuses d'adénines substituées en position 6, on annule la polarité de la néoformation et on provoque une intense multiplication de points caulinaires. Il y a par contre inhibition de la rhizogenèse à partir de la concentration de 10−4 M; elle s'accompagne d'une perte de la dominance et d'un arrêt de la croissance. Une telle stimulation du bourgeonnement est obtenue dans les mêmes conditions en milieu gelosé avec le Begonia gigantea Wall., Begonia socotrana Hook, et, à un très faible degré, avec le Begonia X « Comte de Miribel » (B. albopicta Mort. X B. corollina Carr.).
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Growth, nutrition and chlorophyll development were studied in chlorophyllous callus tissues isolated from the following edible angiospermous plants: carrot root, crown gall of tomato, endive embryo, leaf petiole and stem of lettuce, leaf petiole of parsley, pea stem and rose stem. Growth patterns of these tissues in vitro were sigmoid. Synthetic media produced less growth, in terms of fresh weight increase, than media containing coconut milk, a highly complex and little understood natural substance. MURASHIGE and SKOOG'S synthetic medium proved useful for satisfactory growth and chlorophyll production in a number of tissues. Its usefulness was further increased by additional amounts of copper sulphate, potassium nitrate and monobasic ammonium phosphate. Increased levels of iron and magnesium inhibited growth. Incorporation of yeast extract in the tobacco-high-salts-medium produced the highest amount of growth and chlorophyll formation in endive tissue. Presence of exogenous sucrose was essential for the continued good growth of the above callus tissues in vitro. Highest amount of growth took place either in white light or in the dark. Different tissues had different responses to high or low intensities of light. Endive and carrot tissues produced in vitro were palatable to human taste. Endive tissue was particularly good as it also differentiated many small rosettes of leaves, shoots and had a mild aromatic flavor typical of the endive plants grown in nature.
Article
The carrot-root tissue culture assay for cytokinin activity has been improved by changing the site of explant excision and eliminating certain vitamins from the basal medium. These modifications increased its sensitivity and enabled zeatin [6-(4-hydroxy-3-methylbut-trans-2-enyl)aminopurine] to be detected at concentrations less than 5×10(-5)μM. In the improved assay, zeatin was markedly more active than kinetin, 6-benzylaminopurine, 6-(o-methylbenzyl)aminopurine and 6-(3-methylbut-2-enyl)aminopurine.The activity of zeatin also exceeded that of kinetin in the etiolated bean-leaf disk expansion assay. Zeatin was markedly more effective than kinetin and 6-(3-methylbut-2-enyl)aminopurine in promoting frond expansion and increasing frond number of Spirodela oligorrhiza cultures grown under continuous illumination. Zeatin was also more active than kinetin and 6-(3-methylbut-2-enyl)aminopurine in increasing frond number of Spirodela cultures grown in darkness. In retarding the senescence of disks of leaves of several species, kinetin was considerably more effective than zeatin which was more active than 6-(3-methylbut-2-enyl)aminopurine. The allylic hydroxyl group in zeatin is therefore a structural feature associated with high cytokinin activity.The relative activities of cytokinins can be very different and even in reverse order in different bioassays. It is suggested that this is due to the mechanism of cytokinin action varying in the different biological systems used.
Article
Cells of a soybean tissue strain, suspended in an aerated liquid medium, caused disappearance of p-coumaric acid from the medium and oxidation of guaiacol, benzidine, pyrogallol, L-dihydroxyphenylalanine and L-epinephrine. Both the disappearance and the oxidations were inhibited by 6-benzylaminopurine (BAP) at a concentration of 0.5 mM. BAP at other concentrations either promoted or inhibited oxidation of epinephrine in precisely the pattern reported earlier for the disappearance of coumarate; therefore, the disappearance of coumarate probably involves its oxidation. The effectiveness of other cytokinins in inhibiting the oxidation was studied. At 0.5 mM, and perhaps even at 0.5 μM, some of the several cytokinins tested inhibited oxygen consumption by the soybean cells. This inhibition, which did not require any of the above metabolizable compounds, was especially marked in the presence of cyanide, azide or Antimycin A, and was detectable in 10 min or less. Either Antimycin A or salicylhydroxamic acid alone promoted O2 consumption but together they were quite inhibitory. The soybean cells apparently have an alternate respiratory pathway and cytokinins may influence its operation. Several cytokinins at 0.5 mM, and perhaps at 0.5 μM, also inhibited oxygen consumption by mitochondrial preparations from the soybean cells, the inhibition being evident in about 20 s. The consumption required a substrate such as malate, succinate or NADH. Cytokinins and related compounds varied in effectiveness as follows: BAP and 6-isopentenyla-minopurine ≥ 9-tetrahydropyranyl-BAP > kinetin, ribosyl-isopentenylaminopurine, 9-methyl-BAP and 9-methoxymethyl-BAP > 6,6-dimethylaminopurine and zeatin (slight activity) > 6-methylaminopurine, nicotinamide and adenine (ineffective). To a great extent this order parallels the order of effectiveness of the compounds in causing cell division. Mitochondria, therefore, may contain a site for an important cytokinin action.
Article
Nicotiana tabacum L. (cultivated tobacco) is an amphiploid resulting from the hybridization of ancestral forms or relatives of N. sylvestris and N. tomentosiformis, N. otophora and N. tomentosa are closely related to the latter. Calluses of N. tabacum, N. sylvestris, N. tomentosiformis and N. otophora and an artificially synthesized amphiploid between N. sylvestris and tomentosiformis (Burk's F5) were induced. Callus induction and subculturing of N. tabacum, N. sylvestris and Burk's F5 were performed in basal medium containing 3.0 mg/l of IAA and 0.2 mg/l of KIN, while callus induction of N. tomentosiformis and N. otophora was performed in basal medium of far higher auxin level. Induced calluses of all species were inoculated in the same shoot-redifferentiation medium, which had given 100% shoot redifferentiation in inoculated calluses of N. tabacum and N. sylvestris. All N. tabacum and N. sylvestris calluses inoculated redifferentiated shoots, whereas N. tomentosiformis and N. otophora calluses did not. The results suggest that genetic factors involved in shoot redifferentiation in N. tabacum are mainly localized in the N. sylvestris genome.
Article
Sixty-nine compounds, mostly purine derivatives and closely related substances, were tested for promotion of growth and regulation of organ formation in the tobacco bioassay to determine relationships between chemical structure and cytokinin activity. Forty-three substances were synthesized in this study, and 13 of these were reported for the first time. N6-Alkyladenines (I) varied in activity over a wide concentration range depending on the length of the alkyl chain. Starting with adenine, detectable at ⩾200 μM, activity increased with the chain length to an optimum for 6-pentylaminopurine detectable at ca. 0–001 μM, and then decreased to reach a barely detectable level for 6-decylaminopurine. The result of the incorporation of polar groups in the side chain was not necessarily reduction in activity. One hydroxyl group, as in zeatin (Id), improved the activity of 6-(γ,γ-dimethylallylamino)purine (Ib) if it affected it at all; two hydroxyl groups, as in 6-(2,3-dihydroxy-3-methylbutylamino)purine strongly reduced activity. Comparisons of 6-isoamylaminopurine with 6-(γ,γ-dimethylallylamino)purine and of other closely related pairs of compounds showed that a double bond in the side chain greatly increased cytokinin activity. Adenine derivatives with cyclic substituents in the N6-position (benzyl-Ic), cyclohexyl-, etc.) showed the same general range of activity, potentiation by unsaturation, and variation in activity with substituent size, etc. as did the alkyl derivatives. Heteroatoms in or on the substituent groups decreased activity (in the case of N or Cl) or had little effect (S for O in furfuryl). Of the mono-substituted adenines only the N6-derivatives definitely possessed cytokinin activity. The 1-(III), 3-(II), or 9-substituted adenines probably are inactive but could be activated by conversion to the N6-isomers. Except for slight activity in tests of high concentrations, which could be ascribed to contaminants, 7-substituted adenines were completely inactive. Modification in the adenine moiety lowered the cytokinin activity, often by 95 per cent or more. Substitution of N for the 8-C atom in kinetin and in 6-benzylaminopurine or S for the 6-amino N atom in 6-(γ,γ-dimethylallylamino)purine did not eliminate but drastically reduced activity in the tobacco bioassay. Elimination of the 6-amino group without substituting another group completely removed activity; thus, the purine derivatives, 1-benzylpurine and 1-(γ,γ-dimethylallyl)purine, were inactive in tests where the 1-adenine derivatives could be activated to give a positive response. Addition of a second substituent on the 1-or 3-position of N6-substituted adenines drastically reduced or eliminated cytokinin activity. It is suggested that the 1-position and possibly also the 3-position must be free. A second substituent in the N6-, 7-, or 9-position of N6-substituted adenine derivatives lowered but did not eliminate activity. Also, the disubstituted 1-adenine derivatives, 1,9-dibenzyladenine and 1,7-dibenzyladenine were active, presumably after rearrangement to the corresponding N6-substituted isomers.
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Article
Structure-activity relationships of cytokinins, which regulate many aspects of plant growth, have been reviewed.
Article
Two factors which markedly promote cell division have been purified from plum fruitlet extracts. One factor was a cytokinin obtained in chromatographically homogeneous form, while the other was identified as myo-inositol. These two factors interacted synergistically to promote cell division in carrot phloem explants. A synergism also existed between the cytokinin and indol-3-ylacetic acid but not between myo-inositol and indol-3-ylacetic acid. The cytokinin was distinguished from kinetin by Chromatographic behaviour and division-promoting activity. Sweet corn kernels were found to contain a cytokinin (termed zeatin) which was indistinguishable from that purified from plums. The crystalline free base was found to induce cell division at 0-1 μg/1. Kinetin was inactive at this concentration. Zeatin was chromatographically indistinguishable from an active substance detected by bioassay in plum fruitlet and corn extracts prepared after enzyme inactivation. Zeatin does not appear to be an artefact produced by enzymic or chemical degradation of another cytokinin.
Article
Structure-activity relationships of cytokinins, which regulate many aspects of plant growth, have been reviewed.
Article
The cytokinin activities of various 6-acylaminopurines, 6-alkylaminopurines, 6-acylamino-9-benzyl-purines as well as a series of isosteric-nitrogen derivatives of N6-(γ, γ-dimethylallyl)adenine (I6Ade) have been tested using the tobacco pith and the pea bud bioassays. The interactions between active, slightly active and inactive compounds have been studied with the last assay. Acylation decreases the biological activity; e.g., N6-benzoyl and N6-furoyladenines are less active than Na6-benzyladenine and kinetin. Substitution at the 9-position reduces (tobacco-pith assay) or suppresses (pea-bud assay) the phytohormonal activity of otherwise active 6-acylaminopurines. In isosteric derivatives, maximum activity occurs when the side chain has the same length as in 16Ade. After the analysis of interactions between more or less active compounds, it is suggested that the differences in cytokinin activity could be related to unequal affinities for a hypothetical receptor site.
Article
Several cytokinins and cytokinin-like adenine derivatives as well as other growth regulatory substances were tested for their effectiveness in promoting cell divisions in cultures of isolated protonema cells of Funaria hygrometrica in order to examine the specificity of the celldivision response and to compare it with the bud-induction effect. Several differences have been found between the two responses, first of all a lack of specificity of the cell-division response, and a strong inhibition of the protonemal cell divisions by 1-,3-,and 9-substituted adenine derivatives which with respect to the bud formation showed no inhibition or even (in the case of 1-isopentenyl- adenine) a slightly promoting effect. The possible role of cytokinins in the bud-induction is discussed, and it is suggested that they affect both the intensity of cell divisions occurring during this process as well as their orientation into a three-dimensional growth pattern of the gametophore buds. Only the latter effect, involving a morphogenetic rearrangement, is a specific one, whereas in the promotion of cell divisions the cytokinins can be replaced by other substances.
Article
Gibberellins, cytokinins, and auxins may regulate plant growth via nucleic acid and enzyme synthesis.
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Graduate School with funds from the Wisconsin Alumni Research Foundation. t Predoctoral fellowship from the Ministry of Education of the Syrian Arab Republic and the Institute of International Education is gratefully acknowledged. I Strong
Supported in part by the University Research Committee of the Graduate School with funds from the Wisconsin Alumni Research Foundation. t Predoctoral fellowship from the Ministry of Education of the Syrian Arab Republic and the Institute of International Education is gratefully acknowledged. I Strong, F. M., in Topics of Microbial Chemistry (New York: John Wiley and Sons, 1958), chap. 3. 2 Miller, C. O., Ann. Rev. Plant Physiol., 12, 395 (1961).
in press. 7 2-Furfuryladenine synthesized by F. S. Okumura, University of Kyoto, and tested in our laboratory (unpublished)
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Rogozinska, J. H., J. Helgeson, and F. Skoog, Physiol. Plant., in press. 7 2-Furfuryladenine synthesized by F. S. Okumura, University of Kyoto, and tested in our laboratory (unpublished). 8Leonard, N. J., and T. Fujii, these PROCEEDINGS, 51, 73 (1964).
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0. Miller, and F. Skoog, Abstracts, 128th Meeting
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Okumura, F. S., M. H. Von Saltza, F. M. Strong, C. 0. Miller, and F. Skoog, Abstracts, 128th Meeting, American Chemical Society, September, 1955. 13 Later patented by M. W. Bullock et al., assignors to American Cyanamid Company, N.Y. (U.S. Patent 3,041,340).