Showing papers on "Zeatin published in 2004"

Molecular characterization of cytokinin-responsive histidine kinases in maize. Differential ligand preferences and response to cis-zeatin.

Abstract: Genes for cytokinin-responsive His-protein kinases (ZmHK1, ZmHK2, and ZmHK3a) were isolated from maize (Zea mays). Heterologous expression of each of the ZmHKs in Escherichia coli having the ΔrcsC and cps∷lacZ genetic background conferred cytokinin-inducibility of lacZ expression on the bacteria. In the recombinant E. coli system, ZmHK1 and ZmHK3a were more sensitive to free-base cytokinins than to the corresponding nucleosides; isopentenyladenine was most effective for ZmHK1, while ZmHK2 tended to be most sensitive to trans-zeatin and the riboside. In contrast to a known cytokinin receptor of Arabidopsis (AHK4/CRE1/WOL), all ZmHKs responded to cis-zeatin (cZ), which generally is believed to be inactive or only weakly active. In cultured maize cells, expression of ZmRR1, a cytokinin-inducible response regulator, was induced by cZ as well as by trans-zeatin. These results strongly suggest that maize cytokinin receptors differ in ligand preference, and that cZ is an active cytokinin at least in maize.

Endogenous cytokinins in three genera of microalgae from the chlorophyta1

Abstract: Nine axenic microalgal (Chlorophyta) strains from three genera (Protococcus, Chlorella, and Scenedesmus) were analyzed for endogenous cytokinins. Cytokinin-like activity was detected using the excised cucumber cotyledon bioassay. Five strains showed no cytokinin-like activity and four strains, low cytokinin-like activity. Ethanolic extracts of the microalgae containing a mixture of deuterium-labeled standards were purified using a combined DEAE-Sephadex octadecysilica column and immunoaffinity column based on wide-range specific mon-oclonal antibodies and analyzed by HPLC linked to a micromass single quadrupole mass spectrometer with an electrospray interface and a photodiode array detector. There were similar trends in cytokinin profiles for the nine microalgal strains investigated, although concentrations did vary. Both isopentenyladenine and isopentenyladenosine were detected in all nine strains. cis-Zeatin and cis-zeatin riboside occurred at higher concentrations than the trans isomers, whereas trans-zeatin-O-glucoside and trans-zeatin riboside-O-glucoside were dominant over the cis isomers. Dihydrozeatin and its conjugates were not detected in any significant amounts. The aromatic benzyladenine always occurred at higher concentrations than benzyladenosine. The topolins were well represented with all three isomers (ortho, meta, and para) being detected, with ortho-topolin and ortho-topolin riboside occurring at higher concentrations than the other isomers. However, for the O-glucosides, the meta isomers (meta-topolin-O-glucoside and meta-topolin riboside-O-glucoside) occurred at higher concentrations than the other isomers. No N-glucosides were detected (isopentenyladenine-9-glucoside, zeatin-9-glucoside, dihydrozeatin-9-glucoside, benzyladenine-9-glucoside, ortho-topolin-9-glucoside, and meta-topolin-9-glucoside). Generally, zeatin and topolin conjugates were the dominant forms of isoprenoid and aromatic cytokinins, respectively. There was no distinct trend in the proportions of isoprenoid to aromatic cytokinins.

Determination of endogenous hormones, sugars and mineral nutrition levels during the induction, initiation and differentiation stage and their effects on flower formation in olive

Abstract: Olive (Olea europaea L.) is one of the most important crop plants grown in the Mediterranean region. Varying levels of hormones, sugars and mineral nutrient are thought to influence flower bud formation. The objective of this study was to evaluate the changes in endogenous sugar, mineral nutrition and hormone levels in leaf, node and fruit samples of ‘Memecik’ olive during the induction, initiation and differentiation periods in on (bearing) and off (non-bearing) years. Leaf, node and fruit samples of mature 15-year-old Memecik olive were used. The samples were taken during the induction, initiation and differentiation periods of olive in on (2000) and off (2001) years. Sugar (glucose, fructose and sucrose), mineral nutrient (N, P, K, Ca, Mg, Fe, Zn, Mn and Cu) and hormone [abscisic acid (ABA), indole acetic acid (IAA), gibberellic acid (GA3, GA4) and zeatin (Z)] levels were determined in on and off years. Hormone and sugar levels were measured by gas chromatography and high-performance liquid chromatography. The K, Ca, Mg, Fe, Mn, Zn and Cu levels were quantified by an atomic absorption spectrophotometry. Nitrogen was determined by the Kjeldahl procedure, and P by a spectrophotometric method. The differences in any of the sugar concentrations, with the exception of fructose, were not significant in on and off years. Hormone levels, however, were significantly different in on and off years. Glucose had the highest concentrations in both years, followed by sucrose and fructose, respectively. The highest macro and micro element concentrations were found to be Ca and Fe, respectively. Thus, the results suggest that carbohydrates and mineral nutrients may not have a direct effect to induce flower initiation. However, high GA3 level exhibited an inhibitory effect on floral formation during the induction and initiation periods. On the other hand, the high concentrations of GA4, ABA and certain cytokinin levels may have a positive effect on flower formation in olive during the induction and initiation periods.

Hormones and shifting ecology throughout plant development

Abstract: Hormones modulate complex suites of ecologically relevant behaviors through interactive cascades of signal transduction; evolutionary changes in the function of a single hormone can result in multiple changes in plant traits. Sites of hormone action and tissue sensitivity change throughout plant ontogeny, as embryos, seedlings, and reproductively mature plants cope with shifting suites of environmental variables and resource availability. Phenotypic plasticity and correlations and trade-offs between life history traits (such as resource use efficiency and allocation to growth and differentiation of meristems) also change as plants age; hormonal changes are central to these shifts. I synthesize evidence from the molecular and physiology literature and present novel data on mangrove propagules, seedlings, saplings, and trees. Together, these data demonstrate that several ecologically important traits are hormonally mediated (both in the short term and over evolutionary time) in the diversification of plant lineages. I focus on two hormones with contrasting action: (1) abscisic acid (ABA), which regulates internal plant osmotic stability, membrane integrity, seed dormancy, and stomatal conductance; and (2) cytokinins (zeatin and allied adenine derivatives), which promote cell division, stimulate growth, delay leaf senescence, enhance the capacity of tissues to act as N sinks, and help to transduce signals of light and nutrient availability. ABA and cytokinin levels are correlated with patterns of osmotic tolerance, photosynthesis, growth, and leaf longevity, and their concentrations in specific tissues change throughout plant development. Ecologists and evolutionary biologists are in a strong position now to creatively comprehend, predict, and potentially engineer plant strategies and adaptive trade-offs over plant lifetimes in light of emerging knowledge of hormones.

In vitro plant regeneration and genotype conservation of eight wild species of Curcuma

Abstract: In vitro protocols for plantlet regeneration and medium-term genotype conservation of eight wild species of Curcuma have been optimized. Both the phenomena were genotype-dependent and influenced significantly by type and concentration of cytokinins used. In general, benzyladenine (BA) was found superior to other cytokinins tested for plantlet regeneration and γ,γ-dimethylallylaminopurine (2iP) for conservation. Number of shoots per culture ranged from 1.3 to 7.2 and conservation period from 264 to 379 d. In 30-d-old cultures, highest frequency of shoot regeneration could be obtained in C. malabarica (7.2 shoots per culture) on MS + 11.4 μM zeatin. Curcuma sp. (unidentified wild species) could be conserved for maximum period (379 d) on MS + 24.6 μM 2iP followed by C. aromatica (363 d) on MS + 22.8 μM zeatin. The tissue culture-raised plantlets were morphologically similar to their parents. The in vitro-conserved plants multiplied rapidly in tissue cultures and produced normal rhizomes upon transfer to soil in net house.

Variations in abscisic acid, indole-3-acetic acid, gibberellic acid and zeatin concentrations in two bean species subjected to salt stress

Abstract: Common bean (Phaseolus vulgaris L.) is sensitive to drought and salinity, while an ancestral legume, tepary bean (P. acutifolius A. Gray) is cultivated successfully where high temperature and drought are common (Lazcano-Ferrat and Lovatt, 1999). Hence, P. acutifolius is a potential source of stress tolerant traits for P. vulgaris through interspecific hybrids. This study comparatively evaluated the effects of salt stress on leaf relative water content (RWC), soluble protein, the phytohormones indole acetic acid (IAA), gibberellic acid (GA3), zeatin, and abscisic acid (ABA) levels in P. vulgaris and P. acutifolius. With the exception of ABA, stress-induced changes in hormonal levels putatively related to stress tolerance have not been investigated previously in either species. Treatment with 50 mM, 100 mM and 150 mM NaCl reduced relative water and protein content in P. vulgaris, but did not affect relative water content and increased protein content in P. acutifolius. Varietal differences between P. vulgaris and P. acutifolius were also observed in hormonal content during the stress period. ABA levels in salt-treated plants of P. vulgaris increased but did not change in P. acutifolius versus the controls. Both IAA and gibberellin levels increased in leaves of P. acutifolius but decreased in P. vulgaris under salt stress. In salt-treated plants, zeatin concentrations in leaves of P. vulgaris decreased within 24–72 h after treatment. However, P. acutifolius responded to all tested NaCl levels by increasing zeatin concentrations after short-term NaCl treatment.

Micropropagation of a local olive cultivar for germplasm preservation

Abstract: In vitro shoot culture was applied to an Italian local cultivar Nebbiara of olive (Olea europaea L.) to preserve its endangered germplasm. This cultivar showed a notable difficulty for the in vitro establishment due to heavy pathogen contamination. Mercury chloride and sodium hypochloride in the sterilisation step and antibiotics in culture media allowed to overcome the problem. Proliferation of shoot apical bud on olive culture medium with 36 g dm−3 mannitol and 4.56 μM zeatin appeared very satisfactory. All the explants tested rooted during a subculture (1 month) preceeded by a 5-d long dark pre-treatment.

Effects of auxins and cytokinins on embryo formation from root-derived callus of Oncidium 'Gower Ramsey'

Abstract: In an attempt to optimize somatic embryo formation in Oncidium ‘Gower Ramsey’, the effects of five auxins (2,4-D, IAA, IBA, NAA and picloram) and five cytokinins (2iP, BA, kinetin, TDZ and zeatin), used alone, was tested in vitro using root-derived callus. In general, kinetin (0.5 and 2 mg l−1) and zeatin (0.5 mg l−1) were found to be more effective than other auxin and cytokinin treatments to induce somatic embryogenesis from root-derived callus.

Clonal Propagation of Dwarf Raspberry (Rubus pubescens Raf.) through in vitro Axillary Shoot Proliferation

Abstract: A protocol for the micropropagation of dwarf raspberry (Rubus pubescens) was developed by the establishment of axenic shoot cultures from greenhouse-grown plants, induction of shoot proliferation, and rooting in vitro. Cultures were initiated from shoot tip and nodal explants on 1/2 strength MS (Murashige T. and Skoog F. 1962. Physiol. Plant. 15:473) macro-salts and MS micro-salts and vitamins containing 8.9 μM N6-benzyladenine (BA) and 0.98 μM indole-3-butyric acid (IBA). Zeatin was more effective than BA, and induced proliferation of about 1.5–2 times as many shoots as BA in combination with 0.54–1.1 μM α-naphthaleneacetic acid (NAA) or 0.49–0.98 μM IBA. With higher zeatin, shoots did not expand and had a high mortality rate. Shoots growing for more than 10 weeks on medium that contained 9.1 μM zeatin occasionally produced adventitious shoot masses, which appeared to arise from dense calluses growing at the base of the shoots in the medium. Shoots were rooted in vitro in the same medium used for shoot proliferation, but without any growth regulators. Almost all (85–90%)in vitro plantlets survived when transferred to potting medium.

Eect of growth regulators on shoot induction and plant regeneration in tomato (Lycopersicon esculentum Mill.)

Abstract: GUBI' ,J ., LAJCHOV` ,Z ., F ARAG” ,J . J ISSN 0006-3088. (Biologia). ISSN 1335-6399 (Biologia. Section Cellular and Molecular Biology). The eect of dierent growth regulators on in vitro growth and plant regeneration of tomato (Lycopersicon esculentum Mill.) explants, derived from hypocotyls and cotyledons of aseptically grown seedlings, was studied. With regard to the regeneration frequency, number of shoot primordia and shoots per explant, the best regeneration medium was the Murashige-Skoog (MS) medium supplemented with 1 mg L 1 of zeatin and 0.1 mg L 1 of indole3-acetic acid. In all genotypes studied, 100% frequency of regeneration was observed when hypocotyl explants were used.

Methyl jasmonate down-regulates endogenous cytokinin levels in cotyledons of Cucurbita pepo (zucchini) seedlings

Abstract: Endogenous cytokinins (CK) were measured in Cucurbita pepo L. (zucchini) cotyledons after spraying 7-day-old seedlings with methyl jasmonate (MeJA) to examine whether the senescence-promoting action of MeJA is associated with changes in metabolic regulation of CK levels. MeJA promoted senescence as estimated by the loss of chlorophyll and injury to chloroplast ultrastructure. This was already detected one day after treatment. The contents of physiologically active CKs determined by high-performance liquid chromatography-mass spectrometry (CK bases: trans-zeatin, dihydrozeatin and isopentenyladenine and their ribosides), especially trans-zeatin and its riboside declined considerably. CK nucleotides and physiologically inactive CK 7- and 9-glucosides were also markedly decreased whereas the content of storage CK O-glucosides as well as cis-isomers of zeatin declined only slightly. Chlorophyll content and the normal chloroplast structure recovered 5 days after the MeJa treatment. The process of photosynthetic apparatus recovery correlated with an increased concentration of physiologically active CKs, especially Z. In contrast, the content of CK nucleotides and storage CK O-glucosides decreased further. We suggest that the ability of MeJA to promote some aspects of senescence in intact zucchini cotyledons is at least partially due to down-regulation of endogenous CK levels and their interconversion between active and inactive forms.

In Vitro Culture of Lowbush Blueberry (Vaccinium angustifolium Ait.)

Abstract: SUMMARY Cultures of three lowbush blueberry (Vaccinium angustifolium Ait.) clones collected from natural stands in Newfoundland were established in vitro on a modified cranberry (V. macrocarpon Ait.) tissue culture medium containing zeatin (5 μM) or N6-[2-isopentenyl]adenine (2iP) (10 μM). Shoot proliferation with respect to shoot number per explant differed among clones at various concentrations of zeatin over two culture periods. Best total shoot proliferation was obtained when basal nodal segments were cultured in the medium supplemented with 2-4 μM zeatin. In another experiment, nodal explants were more productive than shoot tips. Shoots growing for more than 12 weeks on media that contained more than 4 μM zeatin occasionally produced adventitious shoot masses, which appeared to arise from dense calli growing at the base of the shoots in the medium. The lower concentration of sucrose and lower irradiance improved shoot proliferation with respect to vigor compared to the control treatments (30 g L_1 an...

Growth and Endogenous Cytokinins of Juniper Shoots as Affected by High Metal Concentrations

Abstract: The growth and the content of endogenous cytokinins (CKs) of current-year-old shoots from juniper plants (Juniperus communis L.) growing over and off ore site were compared. The juniper shoots from ore site (M plants) had higher metal content and exhibited delayed growth. Less bases and nucleosides of Z- and iP- type CK and more iP-conjugates were present in the M shoots. These changes were probably due to inhibited CK export from the roots and/or altered CK metabolism forming less biologically active CKs.

The role of cytokinins and thidiazuron in the stimulation of somatic embryogenesis in key members of the Restionaceae

Abstract: Rushes are important understorey species and comprise a significant component of pre-mined ecosystems. Re-establishment of rushes into disturbed sites has often been problematic. Several cytokinins and thidiazuron were investigated for the stimulation of somatic embryogenesis in key members of the Restionaceae. Somatic embryogenesis was observed for Desmocladus flexuosus (R.Br.) B.G.Briggs & L.A.S.Johnson with benzyladenine (BA) at 1, 5 or 15 μM alone and 1 μM 2,4-dichlorophenoxyacetic acid (2,4-D). The response to zeatin (Z) and 2iP-6-γ-γ-dimethyl-allyamino-purine (2iP) was negligible. For Baloskion tetraphyllum (J.J.H. de Labillardiere) B.G.Briggs & L.A.S.Johnson and Lyginia imberbis R.Br., BA, Z and 2iP were ineffective in stimulating any response. Somatic embryogenesis was achieved for B. tetraphyllum on 1/2-strength Murashige Skoog (1/2 MS) + 1 μM 2,4-D, with an estimated 14 000 somatic embryos produced from 1 g of plant material. All somatic embryos converted into plantlets and were successfully transferred to soil. Investigation of thidiazuron (TDZ) at 5 and 10 μM and 1 μM 2,4-D demonstrated that young coleoptiles (5–7 days) of B. tetraphyllum produced significantly more somatic embryos (168-fold more) than did older coleoptiles (>14 days). For D. flexuosus, leaf basal portions produced somatic embryos on 5 and 10 μM TDZ, and 5 μM TDZ + 1 μM 2,4-D. Proliferation of 'secondary somatic embryos' was also successful when somatic embryos were initiated on 10 μM TDZ and transferred to 1/2 MS (~9-fold increase). This study demonstrated variation in response among species of the same family, with D. flexuosus responding to BA and TDZ and B. tetraphyllum responding only to 2,4-D. The protocol investigated has the potential to be commercially viable with over 14 000 somatic embryos produced in 6 weeks for B. tetraphyllum.

The Role of Cytokinins and Ethylene in Bean Cotyledon Senescence. The Effect of Free Radicals

Abstract: During ageing of bean (Phaseolus vulgaris L.) cotyledons in plants with modified life span the time-course of four cytokinins, ethylene, and the end products of free radical attack, lipofuscin-like pigments (LFP), were studied. UV irradiation shortened cotyledon life span, while epicotyl decapitation prolonged it. In controls, LFP increased at the senescence onset but at the end of life span it returned to the initial level. Ethylene increased more than 3-fold at the time of abscission. The content of individual cytokinins (zeatin, zeatin riboside, isopentenyl adenine, isopentenyl adenine riboside) varied differently during ageing but they did not decreased in any case under level observed in young cotyledons at the time of abscission. UV irradiation resulted in 14-fold increase in LFP concentration at the end. Ethylene increased 8-fold 2 h after irradiation. Individual cytokinins increased after UV irradiation to a different extent and time-course, nevertheless cotyledon life span was shortened. Decapitation induced LFP decrease. On day 13, LFP abruptly increased and than decreased and stayed lowered until abscission. Ethylene was maximum on day 24, at the time of abscission, it was above 200 % of control. Decapitation produced transient decrease in some cytokinins namely zeatin and isopentenyl adenine riboside.

Flax anther culture: effect of genotype, cold treatment and media

Abstract: We report on screening of wide range of flax cultivars for androgenic response and on testing of induction conditions for flax (Linum usitatissimum L.) anther culture and plant regeneration. Anthers were cultured on four different media: Mo, N6, MS and N&N supplemented with various combinations of growth regulators. The induction of callus formation from cultured anthers was the highest on N6 (with cultivar PR FGL 77 – 12 %) and N&N media (with cultivar Carolin – 2.8 %), preferentially after cold pretreatment (7days at 8 °C). Shoots were formed on calli derived from the microspores inside the cultured anthers on media N&N and N6 supplemented with 1 mg l−1 zeatin or 1 mg l−1BAP + 1 mg l−1NAA, respectively and elongated on MS medium supplemented with 2 mg l−1 zeatin. The highest number of shoots (120) was observed with cultivar Red Wing. Shoots were rooted on MS medium supplemented with 2 mg l−1IAA. Our experiments resulted in total in 62 % anther response and 155 plants regenerated and transferred into soil.

Somatic embryogenesis, organogenesis, and regeneration from leaf callus culture of Decalepis hamiltonii Wight & Arn., an endangered shrub

Abstract: A novel protocol has been developed for inducing somatic embryogenesis from leaf cultures of Decalepis hamiltonii. Callus was obtained from leaf sections in Murashige and Skoog (MS) medium supplemented with α-naphthaleneacetic acid (NAA)+N6-benzyladenine (BA) or 2,4-dichlorophenoxyacetic acid (2,4-D)+BA. Nodular embryogenic callus developed from the cut end of explants on media containing 2,4-D and BA, whereas compact callus developed on media containing NAA and BA. Upon subsequent transfer of explants with primary callus onto MS media containing zeatin and/or gibberellic acid (GA3) and BA, treatment with zeatin (13.68μM) and BA (10.65 μM) resulted in the induction of the highest number of somatic embryos directly from nodular tissue. The maturation of embryos took place along with the induction on the same medium. Embryogenic calluses with somatic embryos were subcultured onto MS basal medium supplemented with 4.56μM zeatin+10.65 μM BA. After 4wk, more extensive differentiation of somatic embryos was observed. The mature embryos developed into complete plantlets on growth regulator-free MS medium. A distinct feature of this study is the induction of somatic embryogenesis from leaf explants of Decalepis hamiltonii, which has not been reported previously. By using this protocol, complete plantlets could be regenerated through indirect somatic embryogenesis or organogenesis from leaf explants in 12–16 wk.

Efficient micropropagation of Vanilla planifolia Andr. under influence of thiadiazuron, zeatin and coconut milk.

Abstract: Vanilla planifolia multiplication through tissue culture was worked out with new leads in elucidation of synergistic activity of zeatin, synthetic cytokinin thidiazuron (TDZ) and coconut milk (CM) as well as N 6 -benzyladenine(BA) . Multiple shoots were developed from axillary bud explants using Murashige and Skoog (MS) medium supplemented with zeatin, BA+zeatin , TDZ and TDZ+ coconut milk (CM). The nature of explant and the method of explant inoculation onto the medium influence not only multiple shoot production, but also bulbous shoot buds (BS) formation. Zeatin supported the growth of mostly single shoots, whereas formation of BS was induced in zeatin and BA combination and also in media supplemented with TDZ+10% CM. Subsequent transfer of these BS onto shoot proliferation medium supplemented with BA (8.87 μM) or α-naphthalene acetic acid (NAA) (2.69 μM) resulted in multiple shoot proliferation 17 ± 2.5 shoots and 30 ± 2.1 shoots respectively per explant. The multiple shoots so obtained were transferred to Nitsch medium (N69) containing BA (2.22 μM) and gibberellic acid (GA3 ) (0.029 μM) and also onto simultaneous shoot multiplication and root forming medium for further growth. For the first time the influence of zeatin, TDZ and coconut milk on shoot multiplication was studied. This protocol is effective in producing micropropagated vanilla plants with successful hardening and field transfer.

Effect of growth regulators on asiaticoside production in whole plant cultures ofCentella asiatica (L) urban

Abstract: We investigated the effects of growth regulators on whole-plant cultures derived from nodes ofCentella asiatica. A B5 liquid medium including 0.01 mg L-1 2,4-D resulted in decreased growth and asiaticoside production. Among the cytokinins tested (TDZ, BA, zeatin, and kinetin), TDZ was the best supplement for the promotion of asiaticoside biosynthesis. To directly estimate this effect, we measured asiaticoside content in the leaf, the main organ for synthesis. The addition of TDZ did not affect asiaticoside accumulation. Nevertheless, our results suggest that treatment with exogenous TDZ may enhance the production of asiaticoside in cultures simply through an increase in biomass.

Micropropagation of Japanese Chestnut (Castanea crenata Sieb. et Zucc.) Seedlings

Abstract: Japanese chestnut (Castanea crenata Sieb. et zucc.) was micropropagated from nodal explants of 2-month-old seedlings, and the regenerated plantlets were acclimatized after potting. For in vitro establishment, 5 μM zeatin was more effective than 5 μM BA or TDZ, and Sato's (BW) medium was as effective as MS(1/2NO 3 ) medium. Driver-Kuniyuki walnut medium produced more shoots showing hyperhydricity symptoms. In the multiplication culture, the higher the concentration of zeatin added to BW medium, the greater the number of shoots showing hyperhydricity, although the longest shoot was obtained when 6.9 μM zeatin was added. After planting in 1/2BW medium with 15 μM IBA for 5 d to induce rooting, shoots planted in 1/2BW medium plus vermiculite gelled with Gellan Gum (SV substrate) rooted better than those in either the gelled medium without vermiculite (S substrate) or vermiculite plus liquid medium (V substrate). One third of the shoots planted in the V substrate died, although 62% of the surviving shoots rooted well. Of the shoots planted in the S substrate, 83% survived, but only 35% of these survived rooting. Shoots rooted in the SV and V substrates survived well after the completion of acclimatization, and shoots rooted in the SV substrate grew more vigorously after potting. Chemical names used: 6-benzyladenine (BA); 6-(4-hydroxy-3-methyl-but-2-enylamino)purine (zeatin); indole-3-butyric acid (IBA); 1-phenyl-3-(1,2,3-thiadiazol-5-yl)urea (thidiazuron, TDZ).

In vitro Plantlets Regeneration of Rose

Abstract: Nodal segments and shoot tips were cultured on MS supplemented with different concentrations and combinations of BAP, NAA and zeatin for multiplying axillary shoots. Among two types of explants, the nodal explants produced the highest number of shoots when they were cultured on MS + 1.5 mg/l BAP + 0.25 mg/l zeatin + l00 mg/l CH. The number of shoots per explant in initial cultures varied from five to seven. But after three weeks when they were subcultured in the same medium, the number of shoots increased with an average of 15 per culture. Shoot tip explants also produced multiple shoots, but their performance was not as good as nodal explants. For best rooting, 34 cm long shoots were excised and implanted individually onto the rooting medium containing half strength MS fortified with 1.0 mg/l IBA and 0.5 mg/l IAA. Within four weeks of transfer to the rooting medium, 85% of the microcuttings produced seven - ten roots. The regenerated plantlets were successfully transferred to soil and the percentage of survivability under ex vitro condition was 80.

Somatic Embryogenesis and Plant Regeneration from in-vitro-grown Leaf Explants of Rose

Abstract: Somatic embryogenesis was initiated from in vitro-grown leaf explants of rose using an induction period of 4 weeks on MS basal medium supplemented with auxin fol- lowed by several subcultures on MS basal medium with cytokinin. '4 th of July' showed the highest regeneration frequency (24.4%) on 5.3 µM NAA followed by culture on medium containing 18.2 µM zeatin. 'Tournament of Roses' produced somatic embryos when cul- tured for 4 weeks on medium containing dicamba, 2.3 µM followed by three subcultures on medium containing 18.2 µM zeatin. Embryogenic callus matured on MS media con- taining 0.5 µM NAA, 6.8 µM zeatin, and 2.9 µM GA 3 . Long-term cultures were established for both cultivars. Somatic embryos germinated on MS medium containing IBA and BA. Silver nitrate (58.8 µM) enhanced shoot formation and germination of somatic embryos. Plants derived from somatic embryos were acclimatized and successfully established in the greenhouse.

Plant regeneration in Actinidia polygama Miq. by leaf, stem, and petiole culture with zeatin, and from stem-derived calli on low-sucrose medium

Abstract: We examined the effect of zeatin on the formation of shoot buds from explants and callus tissues derived from stem segments of Actinidia polygama Miq. (matatabi or silver vine). Stem and petiole segments cultured on combined broad-leaved tree medium and woody plant medium (BW medium) supplemented with zeatin for 40 days formed many shoot buds. Callus tissues derived from the stem segments and subcultured on BW medium supplemented with 6-benzyladenine and 1-naphthaleneacetic acid formed shoot buds when the medium contained 13.7μM zeatin. BW medium containing low concentrations of sucrose strongly induced the formation of shoot buds from the callus.

Changes in Phytohormone Status in Stems and Roots after Decapitation of Pea Seedlings

Abstract: Experiments were performed on the first and second internodes and 4-cm-long apical segments of main roots of pea (Pisum sativum L) seedlings, grown in the light and decapitated above the second node on the seventh day after seed germination Endogenous phytohormones were measured by the enzyme-linked immunosorbent assay during three days after decapitation of seedlings The IAA level in the internodes decreased 2–3 times on the second day after decapitation of seedlings while the cytokinin level increased 5–6 times for zeatin and zeatin riboside (Z and ZR) and 15–2 times for isopentenyl adenine and isopentenyl adenosine (IP and IPA) In contrast to internodes, the IP and IPA contents in the roots of decapitated seedlings did not change, but the levels of Z and ZR increased 15–2 times compared to intact plant roots The IAA level in the apical region of root remained almost unchanged after the removal of shoot apex It was concluded that the apical meristem of the main root is not the site of the cytokinin response to the auxin signal coming from the stem apex and that a slight accumulation of Z and ZR after decapitation is due to upper zones of the root There was no difference in the content of gibberellin-like substances between the internodes of intact and decapitated seedlings However, the content of gibberellins (GA) in the root tip decreased after decapitation of seedling, which suggests an essential role of apical bud in supplying the root with GA and/or intermediates for their biosynthesis

The Rg‐1 encoded regeneration capacity of tomato is not related to an altered cytokinin homeostasis

Abstract: Summary • Cytokinin (CK) metabolism was analyzed in tomato (Lycopersicon esculentum) Rg-1 hybrids during in vitro shoot organogenesis from root explants. • Data were obtained by combining physicochemical analysis with quantification and in situ detection methods. • Although exogenous zeatin is added in all classical regeneration protocols, we show here that regenerating (Rg+) tomato explants did not require an exogenous CK source for regeneration. Irrespective of the presence or absence of exogenous zeatin, the endogenous CK levels were not affected by Rg-1 in the initial explants or in the early callus phase. In a later stage, and related to the presence of numerous shoots, the Rg+ explants showed much lower endogenous CK concentrations than the nonregenerating (rg−) explants. Cells of rg− explants were not able to differentiate, despite their high endogenous CK content, and did not respond to exogenously applied CKs. • We show that the insensitivity of rg− explants to a hormonal signal, normally initiating regeneration, is not related to an altered endogenous CK metabolism. We therefore postulate that Rg-1 action involves a regeneration-specific CK receptor or a regeneration-specific CK signal transduction pathway.

Effects of different cytokinins on the shoot regeneration from apple leaves of 'Royal Gala' and 'M.26'

Abstract: The effects of different types of cytokinins on the shoot regeneration from leaf explants of apple scion 'Royal Gala' and apple rootstock 'M.26' were evaluated. Regeneration media contained either thidiazuron, or 6-benzylaminopurine, or meta-topolin, or zeatin, or kinetin, or their N9-ribosides, respectively, in the concentration range 0.5 to 8.0 mg 1-1. Effects of 'these cytokinins were evaluated on the percentage of regeneration (R%) and that of vitrification (V%) and on the number of regenerated shoots per explant (SN). Organogenetic index (0I) calculated from these data was used for the evaluation of efficacy of cytokinins. The course of shoot organogenesis also was followed using stereomicroscope. Types and concentrations of cytokinins applied in the regeneration media influenced each parameter significantly and the regeneration answer was strongly genotype-dependent. The best regeneration (SN: 11.08, 01: 7.5) was achieved in `Royal Gala' by using TDZ in concentration of 0.5 mg 1-1 (2.271,1M). There was a clear relationship between the effect on the regeneration efficacy and the chemical structure of cytokinins considering classical cytokinins, namely N9-ribosides applied in less concentration than non­ribosides have the same or best regeneration effects except for 6-benzylaminopurine riboside. However, similar relationship could not be detected in the case of 'M.26'. SN was the highest (3.22) using 6.5 mg 1-1 (18.2011M) 6-benzylaminopurine riboside or 8.0 mg 1-1 (21.44 µM) meta-topolin riboside (3.18). SN was not significantly lower (3.12) by using 2.0 mg 1-1 (9.08 1M) TDZ, however, OI was about half as big (0.63 compared to 1.29 or 1.74 with 6-benzylaminopurine riboside or meta-topolin riboside, respectively). 'Royal Gala' had higher organogenetic ability, than `M.26': 3.5-fold higher shoot number per explant and more than 4-fold higher organogenetic index was reached with this cultivar than with 'M.26'. Moreover, the similar developmental stage of shoots could be observed 3-5 days earlier than in 'M.26' and if explants of 'Royal Gala' were further cultured with 3 weeks, SN increased from 11.08 to 24.42 on TDZ-containing regeneration medium, which might suggest higher organogenetic ability, too.