Showing papers on "Zeatin published in 2006"

Auxin, gibberellin, cytokinin and abscisic acid production in some bacteria

Abstract: In this study, auxin (indole-3-acetic acid), gibberellin, cytokinin (zeatin) and abscisic acid production were investigated in the culture medium of the bacteria Proteus mirabilis, P. vulgaris, Klebsiella pneumoniae, Bacillus megaterium, B. cereus, Escherichia coli. To determine the levels of these plant growth regulators, high performance liquid chromatography (HPLC) technique was used. Our findings show that the bacteria used in this study synthesized the plant growth regulators, auxin, gibberellin, cytokinin and abscisic acid.

Effect of partial rootzone drying on the concentration of zeatin-type cytokinins in tomato (Solanum lycopersicum L.) xylem sap and leaves

Abstract: Decreased cytokinin (CK) export from roots in drying soil might provide a root-to-shoot signal impacting on shoot physiology. Although several studies show that soil drying decreases the CK concentration of xylem sap collected from the roots, it is not known whether this alters xylem CK concentration ([CK xyl ]) in the leaves and bulk leaf CK concentration. Tomato (Solanum lycopersicum L.) plants were grown with roots split between two soil columns. During experiments, water was applied to both columns (well-watered; WW) or one (partial rootzone drying; PRD) column. Irrigation of WW plants aimed to replace transpirational losses every day, while PRD plants received half this amount. Xylem sap was collected by pressurizing detached leaves using a Scholander pressure chamber, and zeatin-type CKs were immunoassayed using specific antibodies raised against zeatin riboside after separating their different forms (free zeatin, its riboside, and nucleotide) by thin-layer chromatography. PRD decreased the whole plant transpiration rate by 22% and leaf water potential by 0.08 MPa, and increased xylem abscisic acid (ABA) concentration 2.5-fold. Although PRD caused no detectable change in [CK xyl ], it decreased the CK concentration of fully expanded leaves by 46%. That [CKxyi] was maintained and not increased while transpiration decreased suggests that loading of CK into the xylem was also decreased as the soil dried. That leaf CK concentration did not decline proportionally with CK delivery suggests that other mechanisms such as CK metabolism influence leaf CK status of PRD plants. The causes and consequences of decreased shoot CK status are discussed.

Crystal Structure of Vigna radiata Cytokinin-Specific Binding Protein in Complex with Zeatin

Abstract: The cytosolic fraction of Vigna radiata contains a 17-kD protein that binds plant hormones from the cytokinin group, such as zeatin. Using recombinant protein and isothermal titration calorimetry as well as fluorescence measurements coupled with ligand displacement, we have reexamined the K d values and show them to range from ∼10 −6 M (for 4PU30) to 10 −4 M (for zeatin) for 1:1 stoichiometry complexes. In addition, we have crystallized this cytokinin-specific binding protein (Vr CSBP) in complex with zeatin and refined the structure to 1.2 A resolution. Structurally, Vr CSBP is similar to plant pathogenesis-related class 10 (PR-10) proteins, despite low sequence identity (

Effects of Cytokinins on In Vitro Seed Germination and Early Seedling Morphogenesis in Lotus corniculatus L.

Abstract: We determined the effects of zeatin (ZEA), isopentenyl adenine (2iP), kinetin (KIN), benzyladenine (BA), and thidiazuron (TDZ) on seed germination, elongation of seedling shoots and roots, frequency of regeneration, and the number of regenerants per seedling in Lotus corniculatus L. Sterilized seeds were cultured in vitro on Murashige and Skoog (1962) medium containing 3% sucrose, 0.7% agar, and various cytokinins (0, 0.08, 0.22, 0.35, 0.80, 2.20, and 3.50 μM). After 30 days, seedlings were transferred to cytokinin-free medium for another 60 days. All cytokinins stimulated the rate and percentage of seed germination at least twofold in optimum concentrations; TDZ and ZEA were the most active, followed closely by BA, whereas KIN and 2iP stimulated germination in higher concentrations only. Elongation of shoots and roots was strongly inhibited at the lowest TDZ and BA concentrations, whereas ZEA, KIN, and 2iP exerted moderate, dose-dependent inhibition. The frequency of regenerant-producing seeds was highest on ZEA and BA, whereas the greatest number of regenerants per seedling was found on TDZ. It is concluded that the culture of seeds on cytokinin-containing media, followed by transfer to cytokinin-free medium, is a suitable procedure for rapid production of a large number of uniform regenerants. The presumed role of particular cytokinins is discussed.

Cytokinin-induced activity of antioxidant enzymes in transgenic Pssu-ipt tobacco during plant ontogeny

Abstract: Cytokinin (CK) content and activities of several antioxidant enzymes were examined during plant ontogeny with the aim to elucidate their role in delayed senescence of transgenic Pssu-ipt tobacco Control Nicotiana tabacum L (cv Petit Havana SR1) and transgenic tobacco with the ipt gene under the control of the promoter of small subunit of Rubisco (Pssu-ipt) were both grown either as grafts on control rootstocks or as rooted plants Both control plant types showed a decline in total content of CKs with proceeding plant senescence Contrary to this both transgenic plant types exhibited at least ten times higher content of CKs than controls and a significant increase of CK contents throughout the ontogeny with maximal values in the later stages of plant development Significantly higher portion of O-glucosides was found in both transgenic plant types compared to control ones In transgenic plants, zeatin and zeatin riboside were predominant type of CKs Generally, Pssu-ipt tobacco exhibited elevated activities of antioxidant enzymes compared to control tobacco particularly in the later stages of plant development While in control tobacco activity of glutathione reductase (GR) and superoxide dismutase (SOD) showed increasing activity up to the onset of flowering and then gradually decreased, in both transgenic types GR increased and SOD activity showed only small change throughout the plant ontogeny Ascorbate peroxidase (APOD) was stimulated in both transgenic types The manifold enhancement of syringaldazine and guaiacol peroxidase activities was observed in transgenic grafts throughout plant ontogeny in contrast to control and transgenic rooted plants, where the increase was found only in the late stages Electron microscopic examination showed higher number of crystallic cores in peroxisomes and abnormal interactions among organelles in transgenic tobacco in comparison with control plant The overproduction of cytokinins resulted in the stimulation of activities of AOE throughout the plant ontogeny of transgenic Pssu-ipt tobacco

The role of sucrose and different cytokinins in the in vitro floral morphogenesis of rose (hybrid tea) cv. “First Prize”

Abstract: Shoots of rose (hybrid tea) cv. “First Prize” were induced to flower in vitro on Murashige and Skoog (MS) medium containing various sucrose concentrations (15, 30 or 45 g l−1) and different phytohormone combinations of different cytokinins [N6-benzyladenine (BA); thidiazuron (TDZ) and zeatin] with α-naphthaleneacetic acid (NAA). Results indicate that sucrose is the key factor in floral morphogenesis while cytokinin increases the flowering percentage and helps the normal development of floral buds. From the three cytokinins that were used, BA and zeatin were considered to be more suitable as inductive flowering agents than TDZ. Reduced inorganic and organic salt concentration in MS media had a positive effect on in vitro flowering. The morphology of shoots bearing floral buds varied with different cytokinin treatments. The highest percentage (45%) of flowering was obtained on MS medium supplemented with 3.0 mg l−1 BA, 0.1 mg l−1 NAA and 30 g l−1 sucrose.

Research article Transgenic ipt tobacco overproducing cytokinins overaccumulates phenolic compounds during in vitro growth

Abstract: We present evidence that overproduction of endogenous cytokinins (CK) caused stress response in non-rooting Pssu-ipt transgenic tobacco (Nicotiana tabacum L.) grown in vitro. It was demonstrated by overaccumulation of phenolic compounds, synthesis of pathogenesis related proteins (PR proteins), and increase in peroxidase (POD) activities. Immunolocalization of zeatin and also PR-1b protein on leaf cryo-sections proved their accumulation in all mesophyll cells of transgenic tobacco contrary to control non-transgenic plants. Intensive blue autofluorescence of phenolic compounds induced by UV in cross-sections of leaf midrib showed enhanced contents of phenolics in transgenic tobacco compared with controls, nevertheless, no significant difference between both plant types was found in leaf total lignin content. Transgenic plantlets exhibited higher peroxidase activities of both soluble and ionically bound fractions compared with controls. HPLC analysis of phenolic acids confirmed the increase in all phenolic acids in transgenic tobacco except for salicylic acid (SA). The effect of high phenolic content on rooting of transgenic tobacco is discussed.

In vitro organogenesis and plant formation in cucumber

Abstract: In vitro organogenesis was achieved from callus derived from hypocotyl explants of Cucumis sativus L. cv. Poinsett 76. Calli were induced from hypocotyl explants excised from 7-d-old seedlings grown on Murashige and Skoog (MS) medium containing 87.64 µM sucrose, 0.8 % agar, 3.62 µM 2,4-dichlorophenoxy acetic acid and 2.22 µM 6-benzyladenine (BA). Regeneration of adventitious buds from callus (25 shoots explant−1) was achieved on MS medium supplemented with 8.88 µM BA, 2.5 µM zeatin and 10 % coconut water after two subcultures in the same medium at 30-d interval. Gibberellic acid (1.75 µM) favoured shoot elongation and indole 3-butyric acid (7.36 µM) induced rooting. Rooted plants were hardened and successfully established in soil.

Microclonal propagation of Vaccinium sp. and Rubus sp. and detection of genetic variability in culture in vitro

Abstract: Five high-bush blueberry, two lingonberry, and six raspberry cultivars were evaluated in terms of their regeneration capacity when propagated in vitro by axillary and adventitious organogenesis. In the high-bush blueberry and the lingonberry, shoots were regenerated from isolated meristems and dormant buds and cultivated on modified Anderson's rhododendron (AN) medium. Shoot formation was induced on medium containing 0.5 mg 1 -1 zeatin. In the high-bush blueberry, the cultivar with the highest shoot proliferation intensity was 'Brigitta', with 14.2 shoots per primary explant. The cultivars with the highest adventitious shoot multiplication were 'Brigitta', with 39.1 shoots/explant, and 'Berkeley', with 18.0 shoots/explant. In the lingonberry, the cultivar with the highest shoot proliferation intensity was 'Red Pearl', with 5.2 shoots per primary explant. The cultivar with the highest adventitious shoot multiplication was 'Red Pearl' with about 44 shoots/explant. In the raspberry, shoots were regenerated from isolated meristems and dormant buds and cultivated on modified MS medium containing 1.0 mg I -1 BAP and 0.1 mg I -1 IBA. The cultivar with the best meristem formation and shoot proliferation was 'Bulharsky Rubin', with 56.6% of the explants producing shoots. Adventitious shoot regeneration was also highest in 'Bulharsky Rubin', with 25.75 of leaf explants producing adventitious shoots on MS medium containing 0.5 mg 1 -1 TDZ and 0.2 mg 1 -1 2,4-D. RAPD proved to be a simple and efficient technique for identifying high-bush blueberry and lingonberry clones, which could easily be distinguished by their characteristic polymorphic banding patterns. However, there were no differences in the DNA profiles of the mother cultivars and any of the clones derived from them. Therefore, either no somaclonal variation occurred during the micropropagation process, or more sensitive techniques are needed to detect it. Flow-cytometry did not detect any changes in ploidy level, which confirms that no relative changes in DNA content took place during the micro-propagation process.

Endogenous cytokinins in shoots of Aloe polyphylla cultured in vitro in relation to hyperhydricity, exogenous cytokinins and gelling agents

Abstract: The process of hyperhydricity in tissue cultured plants of Aloe polyphylla is affected by both applied cytokinins (CKs) and the type of gelling agent used to solidify the medium. Shoots were grown on media with agar or gelrite and supplemented with different concentrations of N6-benzyladenine (BA) or zeatin (0, 5 and 15 μM). Endogenous CKs were measured in in vitro regenerants after an 8-weeks cycle to examine whether the hyperhydricity-inducing effect of exogenous CKs and gelling agents is associated with changes in the endogenous CK content. On media with agar a reduction in hyperhydricity occurred, while the gelrite treatment produced both normal and hyperhydric shoots (HS). The content of endogenous CKs, determined by HPLC-mass spectrometry, in the shoots grown on CK-free media comprised isopentenyladenine-, trans-zeatin- and cis-zeatin-type CKs. The application of exogenous CKs resulted in an increase in the CK content of the shoots. Following application of zeatin, dihydrozeatin-type CKs were also detected in the newly-formed shoots. Application of BA to the media led to a transition from isoprenoid CKs to aromatic CKs in the shoots. Shoots grown on gelrite media contained higher levels of endogenous CKs compared to those on agar media. Total CK content of HS was higher than that of normal shoots grown on the same medium. We suggest that the ability of exogenous CKs and gelrite to induce hyperhydricity in shoots of Aloe polyphylla is at least partially due to up-regulation of endogenous CK levels. However, hyperhydricity is a multifactor process in which different factors intervene.

Zeatin overcomes thidiazuron-induced inhibition of shoot elongation and promotes rooting in strawberry culture in vitro

Abstract: The effects of 0, 2, 4 or 8 µM thidiazuron (TDZ) and explant type on adventitious shoots regenerated on excised leaf disks, sepals (calyx) and petiole halves of greenhouse-grown ‘Bounty’ strawberry...

Zeatin accumulation and misexpression of a class I knox gene are intimately linked in the epiphyllous response of the interspecific hybrid EMB-2 ( Helianthus annuus × H. tuberosus )

Abstract: Epiphylly, occurring in a somaclonal variant (EMB-2) of the interspecific hybrid Helianthus annuus × H. tuberosus, was used to investigate molecular and cyto-physiological mechanisms that underlie cellular fate change. EMB-2 plants are characterized by profuse proliferation of shoot- and embryo-like structures on some leaves. We addressed the putative relationship between cytokinins and knox genes in EMB-2 plants. A class I knox gene, HtKNOT1, was isolated from H. tuberosus. A high level of HtKNOT1 transcripts was detected in EMB-2 epiphyllous leaves compared to non-epiphyllous (NEP) ones. In addition, epiphylly was related to a localized increases in zeatin and N-glycosylated cytokinins. As ectopic morphogenesis proceeded, HtKNOT1 transcripts and zeatin co-localized and showed different patterns in ectopic shoot compared with embryo-like structures, consistent with the differential role of both cytokinin and knox genes in the two morphogenetic events. Notably, a massive shoot/embryo regeneration was induced in EMB-2 NEP leaves by in vitro zeatin treatment. These results clearly indicate that localized cytokinin accumulation and ectopic expression of HtKNOT1 are closely linked in the epiphylly of EMB-2 plants.

Arabidopsis cytokinin-resistant mutant, cnr1 , displays altered auxin responses and sugar sensitivity

Abstract: Based upon the phenotype of young, dark-grown seedlings, a cytokinin-resistant mutant, cnr1, has been isolated, which displays altered cytokinin- and auxin-induced responses. The mutant seedlings possess short hypocotyls and open apical hooks (in dark), and display agravitropism, hyponastic cotyledons, reduced shoot growth, compact rosettes and short roots with increased adventitious branching and reduced number of root hairs. A number of these features invariably depend upon auxin/cytokinin ratio but the cnr1 mutant retains normal sensitivity towards auxin as well as auxin polar transport inhibitor, TIBA, although upregulation of primary auxin-responsive Aux/IAA genes is reduced. The mutant shows resistance towards cytokinin in hypocotyl/root growth inhibition assays, displays reduced regeneration in tissue cultures (cytokinin response) and decreased sensitivity to cytokinin for anthocyanin accumulation. It is thus conceivable that due to reduced sensitivity to cytokinin, the cnr1 mutant also shows altered auxin response. Surprisingly, the mutant retains normal sensitivity to cytokinin for induction of primary response genes, the type-A Arabidopsis response regulators, although the basal level of their expression was considerably reduced as compared to the wild-type. The zeatin and zeatin riboside levels, as estimated by HPLC, and the cytokinin oxidase activity were comparable in the cnr1 mutant and the wild-type. The hypersensitivity to red light (in hypocotyl growth inhibition assay), partial photomorphogenesis in dark, and hypersensitivity to sugars, are some other features displayed by the cnr1 mutant. The lesion in the cnr1 mutant has been mapped to the top of chromosome 1 where no other previously known cytokinin-resistant mutant has been mapped, indicating that the cnr1 mutant defines a novel locus involved in hormone, light and sugar signalling.

Somatic embryogenesis and plantlet regeneration in Sorghum bicolor (L.) Moench, from leaf segments

Abstract: Efficient plant regeneration system from leaf disc segments of S o rghum (Sorghum bicolor (L.) Moench) was developed. The factors affecting the somatic embryo formation and regeneration capacity of leaf segments of six genotypes; IS 3566, SPV 475, CSV 13, CSV 15, CAV 112 and IS 348, were investigated. The highest number of somatic embryos was obtained on MS medium supplemented with 2 mgl -1 2,4,5-T + 1 mgl -1 Zeatin in dark conditions. Highest frequency of embryogenic callus and somatic embryo formation were observed in IS 3566. The highest plantlet regeneration was obtained after transfer of embryogenic calli to regeneration medium supplemented with 2.5 mgl -1 TDZ (14 plantlets per segment). Rooting of shoots was noticed on the NAAmedium. A mean of 30 ‐ 1.05 root intact plantlets was recovered per explant. The rooted plantlets were well accomplished with a survival frequency of 96%. Moreover, there were no phenotypic differences observed between the in vitro regenerated and i n v i v o plantlets.

Role of phytohormones in organogenic ability of elm multiplicated shoots

Abstract: The study presents the comparative analyses of endogenous contents of auxin (IAA), cytokinins (CKs), polyamines (PAs), and phenolic acids (PhAs) in apical and basal parts of elm multiplicated shoots with regard to the organogenic potential. The shoot-forming capacity was higher in the apical part than in the basal part. However, the timing of root formation was in the apical type of explant significantly delayed (compared with the organogenic potential of basal part). Significantly higher contents of free bases, ribosides and ribotides of isopentenyl adenine, zeatin and dihydrozeatin that were found in the apical segments, might be considered as the most important factor affecting in vitro shoot formation. The content of endogenous free IAA was approximately three times higher in the basal shoot parts than in the apical parts. The amounts of putrescine and spermidine were higher in the apical part which generally contains less differentiated tissues than the basal part of shoot. The predominant PhA in both types of explants was caffeic acid, and concentrations of other PhAs decreased in the following order: p-coumaric, ferulic, sinapic, vanillic, chlorogenic, p-hydroxybenzoic and gallic acids. The contents of all determined PhAs in their free forms and higher contents of glycoside-bound p-coumaric, ferulic and sinapic acids, precursors for lignin biosynthesis, were found in the basal parts.

[Sugar beet (Beta vulgaris L.) morphogenesis in vitro: effects of phytohormone type and concentration in the culture medium, type of explants, and plant genotype on shoot regeneration frequency].

Abstract: In vitro regeneration techniques have been optimized for seven strains and cultivars of sugar beet (Beta vulgaris L.) bred in Russia. The frequency of shoot regeneration from somatic cells and tissues of sugar beet varies from 10 to 97% depending on the explant type, culture-medium composition, and genotype. The in vitro regeneration potential has been estimated in plants with different genotypes. The effect of medium composition (phytohormones and carbohydrates) on the frequency of the formation of a morphogenic callus competent for plant regeneration has been determined. The effect of the types and concentrations of various cytokines (zeatin, kinetin, and 6-benzylaminopurine) on direct shoot regeneration from cotyledon nodes has been estimated. The culture-medium composition has been optimized for direct shoot regeneration from petioles. The effects of different concentrations of abscisic acid on the frequency of shoot regeneration from a morphogenic callus has been studied. Micropropagation has been used to obtain petiole explants and reproduce the shoots obtained by direct regeneration from cotyledonnodes, petioles, and calluses. Improved shoot-regeneration methods can be used for both agrobacterial and bioballistic genetic transformation of the sugar beet genotypes studied.

Efficient and repetitive production of leaf-derived somatic embryos of Oncidium

Abstract: Oncidium cultivars gave different embryogenic responses of leaf explants when affected by auxins (2,4-D, IAA, IBA and NAA), cytokinins (2iP, BA, kinetin, TDZ and zeatin), sucrose, NaH2PO4, casein hydrolysate, peptone, and glutamine. The best embryogenic responses of cv. Sweet Sugar were at 20 g dm−3 sucrose, 85 mg dm−3 NaH2PO4 and 3 mg dm−3 kinetin, respectively. The development of somatic embryos on leaf explants of cv. Sweet Sugar was delayed for about 10 – 20 d in comparison with cv. Gower Ramsey. On growth regulator-free medium, about 40 % of leaf derived embryos of cv. Gower Ramsey were fused together in their basal parts and so called multiple-state embryos. However, under the same condition, the embryos of cv. Sweet Sugar were all in multiple-state form.

Hormone-regulated inflorescence induction and TFL1 expression in Arabidopsis callus in vitro.

Abstract: To study hormone-regulated inflorescence development, we established the in vitro regeneration system of Arabidopsis inflorescences in the presence of cytokinin and auxin. Media containing a combination of thidiazuron (TDZ) and 2,4-dichlorophenoxyacetic acid (2,4-D) were used to induce callus formation. Higher frequencies of calli were obtained by using the inflorescence stems as explants. After transferring the calli to media containing a combination of zeatin and indole-3-acetic acid (IAA), the inflorescences were induced from the calli. The morphology of regenerated inflorescences was similar to that of inflorescences in plants; however, flowers of regenerated inflorescences often lacked a few floral organs. Furthermore, TFL1, a gene involved in floral transition in Arabidopsis, was activated during the inflorescence induction. Our results suggest that the TFL1 gene plays an important role in hormone-regulated inflorescence formation.

Cytokinins inhibit epiphyllous plantlet development on leaves of Bryophyllum (Kalanchoë) marnierianum

Abstract: When leaves of Bryophyllum marnierianum are detached from the plant, plantlets develop from primordia located at their margins. Leaves excised with a piece of stem attached do not produce plantlets. Severing the major leaf veins overcomes the inhibitory effect of the attached stem, indicating that the control agent is transmitted through the vascular system. A possible mechanism is that an inhibitory substance, possibly a known plant hormone, transported from the stem to the leaf, suppresses plantlet development. A number of hormones were tested for their ability to inhibit plantlet primordium development in whole isolated leaves. Auxins had no effect, indicating that apical dominance is not involved. The cytokinins zeatin, kinetin, and benzylaminopurine (BAP) strongly inhibited plantlet development, suggesting that they may be the or a factor involved in maintenance of plantlet primordium dormancy when the leaf is attached to the plant. This hypothesis was strongly supported by the finding that treatment of leaves attached to stems with a cytokinin antagonist (purine riboside) released the primordia from inhibition. In contrast to whole leaves, plantlet primordium development on leaf explants incubated on Murashige Skoog medium containing 3% sucrose was strongly stimulated by cytokinins. A possible explanation of these observations is that in whole leaves the cytokinin signal is transduced into an inhibitory signal whereas in the isolated primordium cytokinin has a direct stimulatory effect. The inhibitory cytokinin pathway must be dominant as long as the leaf is attached to the plant. A model is proposed which could explain these findings. This study points to a novel role of cytokinins in the maintenance of foliar plantlet primordium dormancy.

Facile plant regeneration from tomato leaves induced with spectinomycin

Abstract: Several studies have been conducted to find a combination of hormones conducive to improve regeneration from different explant tissues, particularly from leaves of tomato, and various responses were recorded to use in experiments. Major focus was to regenerate maximum number of shoots from tomato leaves Cv. Moneymaker, Packet, Nagina and Aroma. Depending on the cultivar used, shoot regeneration varied (Moneymaker ≥ Packet ≥ Nagina ≥ Aroma) on RMOT medium (MS salts supplemented with 1mg/L Zeatin and 1mg/L IAA). In addition, several other media were used to compare regeneration efficiencies including RMOP medium containing MS salts supplemented with 0.1mg/L NAA, 1mg/L BAP, 1mg/L thiamine and 100mg/L Myo-inositol. In cultures where negative factors were eliminated, shoot regeneration reached to an average of 9 plants on RMOT medium from each leaf section of 3x3 mm size of cultivar Moneymaker.

Factors affecting seed germination and seedling growth of terrestrial orchids cultured in vitro

Abstract: The effect of two sterilization substances (calcium hypochlorite and sodium hypochlorite) on the germination rate, and the effect of nitrogen and growth regulators on seedling growth and development, was studied in three critically endangered species of terrestrial orchids (Dactylorhiza incarnata subsp. serotina, Dactylorhiza maculata subsp. maculata, Liparis loeselii). Surface sterilization of mature seeds using 7.2% calcium hypochlorite (until decolorization from brown to ivory) stimulated the germination rate. Addition of peptone at 1 g l -1 concentration or auxin 3-indoleacetic acid (IAA; 1.43 μM) with cytokinin zeatin (0.72 μM) and 1-naphthylacetic acid (NAA; 1.34 μM) to the culture medium significantly increased the growth parameters of seedlings after 12

How can different cytokinins influence the process of shoot regeneration from apple leaves in '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 (TDZ), or benzyladenine (BA), or meta-topolin (TOP), or zeatin (ZEA), or kinetin (KIN), or their N 9 -ribosides, respecttively, in the concentration range 0.5 to 8.0 mg L -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) and organogenetic index (OI) calculated from these data. 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, OI: 7.5) was achieved in 'Royal Gala' by using 0.5 mg L -1 TDZ. There was a clear relationship between the effect on the regeneration efficacy and the chemical structure of cytokinins considering classical cytokinins. In 'M.26' SN was the highest (3.22) using 6.5 mg L -1 BAR or 8.0 mg L -1 TOPR (3.18). SN was not significantly lower (3.12) by using 2.0 mg L -1 TDZ; however, OI was about half as big (0.63 compared to 1.29 or 1.74 with BAR or TOPR, respectively). 'Royal Gala' had higher organogenetic ability, than 'M.26': 3.5-fold higher SN and more than 4-fold higher OI 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'.

Comparison of effects of bacterial strains differing in their ability to synthesize cytokinins on growth and cytokinin content in wheat plants

Abstract: The content of cytokinins and pigments together with the morphological parameters and fresh weight were estimated in durum wheat (Triticum durum Desf.) plants 2–4 days after introduction into their rhizosphere of an aliquot of Bacillus suspension using the strains that differed in their ability of producing cytokinins. The experiments were performed under laboratory conditions at the optimum light intensity and mineral nutrition. Inoculation with microorganisms incapable to synthesize cytokinins did not affect the total cytokinin content in the wheat plants, whereas the presence of cytokinin-producing microorganisms in the rhizosphere was accompanied by a considerable increase in the total cytokinin content and the accumulation of individual hormones. On the second day after inoculation, a dramatic increase in zeatin riboside and zeatin O-glucoside contents was observed in the roots, and at the next day the accumulation of zeatin riboside and zeatin was registered in the shoots of treated plants. The increase in cytokinin content promoted plant growth (the increased leaf length and width and a faster accumulation of plant fresh and dry weight). Plant treatment with a substance obtained from microorganisms incapable to synthesize hormones resulted in the insignificant growth stimulation. Plant treatment with a substance obtained from cytokinin-producing microorganisms increased leaf chlorophyll content; in this case, the level of chlorophylls was comparable to that observed in the plants treated with a synthetic cytokinin benzyladenine. The role of cytokinins of microbial origin as a factor providing for growth-stimulating effect of bacteria on plants is discussed.

Efficient somatic embryogenesis and plant regeneration from long-term cell suspension cultures of medicago truncatula cv. jemalong

Abstract: Plants were suecessfully regenerated via somatic embryos from 3-yr-old cell suspension cultures of Medicago truncatula Gaertin. cv. Jemalong line M9-10a. The cultures were originally initiated from callus induced in well-expanded leaflets of 30 d in vitro-grown plants, Suspension cultures were established in stirred-liquid Murashige and Skoog (MS) basal salts and vitamins supplemented with 2.3 μM 2.4-dichlorophenoxyacetic acid (2,4-D) and 2.3 μM kinetin (Kin) and subeultured weekly. Somatic embryogenesis induction step was conducted in liquid MS medium containing 0.45 μM 2,4-D and 0.91 μM zeatin (Zea), during 1,2, and 3wk after subculture. Induced and non-induced cultures were transferred to solid embryo proliferation medium [EPM-MS basal salts and vitamins solidified with 0.2% (w/v) gelrite]. Somatic embryos developed until the late torpedo/dicotyledonary stages. We found that the best condition for the development of somatic embryos was achieved when suspension cultures were not subjected to the induction step. Induction of 1 and 2 wk led to a decrease in the recovery of somatic embryos and the 3-wk treatment resulted in no differentiation of somatic embryos. Plant regeneration was obtained in all conditions (except for 3wk induction) when embryos were transferred to an embryo conversion medium [ECM, similar to EPM but solidified with 0.7% (w/v) agar]. Embryo conversion rates were 54.5±1.6, 52.5±18.5, and 41.6±8.4% for 0, 1, and 2 wk induction treatments, respectively. These plants were successfully transferred to the greenhouse where they matured and produced seeds.