Showing papers on "Zeatin published in 1998"

Uniconazole-induced alleviation of freezing injury in relation to changes in hormonal balance, enzyme activities and lipid peroxidation in winter rape

Abstract: Winter rape (Brassica napus L cv 601) seedlings were treated with 50 mgl-1 of foliar-applied uniconazole and then exposed to freezing stress with a light/dark temperature regime of 2 °C/−3 °C for 5 days at the seedling stage Stressed plants contained lower endogenous GA3 and IAA contents than the controls, while zeatin and ABA contents and ethylene levels were significantly increased Uniconazole-treated plants had lower endogenous GA3 and IAA contents, and higher zeatin and ABA contents and ethylene levels Leaf chlorophyll content and respiratory capacity of roots were reduced significantly after plants were subjected to freezing stress, and foliar sprays of uniconazole retarded the degradation of chlorophyll and increased respiratory capacity of roots Uniconazole-induced freezing tolerance was accompanied by increased activities of various antioxidant enzymes, including superoxide dismutase, catalase and peroxidase Foliar applications of uniconazole reduced electrolyte leakage and malondialdehyde accumulation caused by freezing stress, suggesting that uniconazole may have decreased freezing-induced lipid peroxidation and membrane damage

Alteration of Hormone Levels in Transgenic Tobacco Plants Overexpressing the Rice Homeobox Gene OSH1

Abstract: The rice (Oryza sativa L.) homeobox gene OSH1 causes morphological alterations when ectopically expressed in transgenic rice, Arabidopsis thaliana, and tobacco (Nicotiana tabacum L.) and is therefore believed to function as a morphological regulator gene. To determine the relationship between OSH1 expression and morphological alterations, we analyzed the changes in hormone levels in transgenic tobacco plants exhibiting abnormal morphology. Levels of the plant hormones indole-3-acetic acid, abscisic acid, gibberellin (GA), and cytokinin (zeatin and trans-zeatin [Z]) were measured in leaves of OSH1-transformed and wild-type tobacco. Altered plant morphology was found to correlate with changes in hormone levels. The more severe the alteration in phenotype of transgenic tobacco, the greater were the changes in endogenous hormone levels. Overall, GA1 and GA4 levels decreased and abscisic acid levels increased compared with wild-type plants. Moreover, in the transformants, Z (active form of cytokinin) levels were higher and the ratio of Z to Z riboside (inactive form) also increased. When GA3 was supplied to the shoot apex of transformants, internode extension was restored and normal leaf morphology was also partially restored. However, such GA3-treated plants still exhibited some morphological abnormalities compared with wild-type plants. Based on these data, we propose the hypothesis that OSH1 affects plant hormone metabolism either directly or indirectly and thereby causes changes in plant development.

cis-Isomers of Cytokinins Predominate in Chickpea Seeds throughout Their Development

Abstract: Trans -isomers of cytokinins (CK) are thought to predominate and have greater biological activity than corresponding cis -isomers in higher plants. However, this study demonstrates a system within which the predominant CK are cis -isomers. CK were measured at four developmental stages in developing chickpea ( Cicer arietinum L. cultivar Kaniva) seeds by gas chromatography-mass spectrometry. Concentrations were highest at an early endospermic fluid stage and fell considerably when the cotyledons expanded. The cis -isomers of zeatin nucleotide ([9R-MP]Z), zeatin riboside ([9R]Z), and zeatin (Z) were present in greater concentrations than those of corresponding trans -isomers: ( trans )[9R-MP]Z, ( trans )[9R]Z, ( trans )Z, or dihydrozeatin riboside. Dihydrozeatin, dihydrozeatin nucleotide, and the isopentenyl-type CK concentrations were either low or not detectable. Root xylem exudates also contained predominantly cis -isomers of [9R-MP]Z and [9R]Z. Identities of ( cis )[9R]Z and ( cis )Z were confirmed by comparison of ion ratios and retention indices, and a full spectrum was obtained for ( cis )[9R]Z. Tissues were extracted under conditions that minimized the possibility of RNase hydrolysis of tRNA following tissue disruption, being a significant source of the cis -CK. Since no isomerization of ( trans )[ 2 H]CK internal standards occurred, it is unlikely that the cis -CK resulted from enzymic or nonenzymic isomerization during extraction. Although quantities of total CK varied, similar CK profiles were found among three different chickpea cultivars and between adequately watered and water-stressed plants. Developing chickpea seeds will be a useful system for investigating the activity of cis -CK or determining the origin and metabolism of free CK.

Biological activity of cytokinins derived from Ortho- and Meta-Hydroxybenzyladenine

Abstract: To determine the structure-activity relationships of natural aromatic cytokinins, the activity of 6-benzylaminopurine (BAP) and its hydroxylated derivatives was compared in three bioassays based on stimulation of tobacco callus growth, retention of chlorophyll in excised wheat leaves, and dark induction of betacyanin synthesis in Amaranthus cotyledons. The aromatic cytokinins 6-(2-hydroxybenzylamino)purine (ortho-topolin) and 6-(3-hydroxybenzylamino)purine (meta-topolin), their 9-ribosides and 9-glucosides, were synthesized by the condensation of 6-chloropurine and its 9-glycosides with the appropriate hydroxybenzylamine. The activity of free bases, 9-ribosides and 9-glucosides was compared with that of BAP, trans-zeatin and their 9-glycosides. Hydroxylation of the benzyl ring in the meta position increased the activity of BAP and its riboside in tobacco callus and chlorophyll retention bioassays, whereas ortho-hydroxylation decreased the activity. In contrast, in the Amaranthus bioassay meta-hydroxylation of BAP substantially decreased its activity. Ribosylation at position 9 had no significant effect on the activity of zeatin, BAP and both topolins. The activity of 9-glucosides of all cytokinins tested was near zero. The biological activity of meta-topolin and its riboside is comparable to that of the most active isoprenoid cytokinin, zeatin, in tobacco callus growth and senescence bioassays. The results establish the existence of a family of endogenous aromatic cytokinins centered around the highly active compound, meta-topolin. We also report here an improved chlorophyll retention bioassay based on incubation of 2.5 cm long detached wheat leaf segments in microtiter plate wells containing 150 µl of cytokinin solution. The consumption of cytokinin to be tested is 0.1 µmol per assay only. The amount as small as 1.5 pmol of substance can be estimated using this biotest.

Differential cytokinin effects on the stimulation of in vitro shoot proliferation from meristematic explants of castor (Ricinus communis L.)

Abstract: A highly efficient and reproducible method of in vitro propagation using meristematic explants has been developed for castor. Embryo axes and shoot tips were cultured on Murashige and Skoog (MS) medium supplemented with 0.5-10.0 mg/l of adenine, N6-benzyladenine (BA), kinetin (Kn), thiadiazuron (TDZ) and zeatin. TDZ (1.0-10.0 mg/l) gave the maximum number of shoots (37.8-40.0) from embryo axes, while BA (2.0 mg/l) was found superior to other cytokinins for obtaining the highest number of shoots (46.7) from the shoot apex. Adenine and Kn at all of the tested concentrations resulted in low proliferation rates from embryo axes. The carryover effect of the cytokinins was tested by subculturing proliferating shoot cultures from various media onto the medium fortified with 0.5 mg/l BA. There was no significant influence of the cytokinins on subsequent proliferation from the two explant types except for TDZ with embryo axes. The number of shoots from TDZ-habituated embryo axes ranged between 36.0 and 81.7, while it varied from 5.7 to 22.0 and 3.7 to 28.3 in axillary buds and embryo axes, respectively, on the other media. For elongation of shoots, gibberellic acid (GA3) (0.1-1.0 mg/l) was added to the medium supplemented with 0.2-0.5 mg/l BA. Incorporation of GA3 (0.1 mg/l) significantly enhanced the frequency of elongated shoots but drastically reduced the multiplication ability. Hence, proliferating shoot clusters were periodically transferred to the medium supplemented with 0.5 and 0.2 mg/l BA for further multiplication and elongation. Well-developed shoots were rooted on half-strength MS medium supplemented with 1.0 mg/l indole-3-butyric acid. The rooted plantlets were acclimatized with more than 60% success.

Embryogenic Competence of Immature Wheat Embryos: Genotype, Donor Plant Environment, and Endogenous Hormone Levels

Abstract: The genotype and the environment in which donor plants grow influence embryogenic competence of immature wheat (Triticum aestivum L.) embryos and levels of endogenous hormones in kernels. We studied relationships between embryogenic competence and hormone levels in kernels and calli of PCYT 10 (highly competent) and Yaqui 50 (nearly incompetent) wheat grown at 15 and 25°C. Endogenous levels of abscisic acid (ABA), indole-3-acetic acid (IAA), and six cytokinins were determined for kernels at 0,4,8, and 12 d past antbesis (DPA). Immature embryos were cultured at 12 DPA and hormone content of calli was determined at 7, 14, 21, and 28 d past culture initiation (DPI). Somatic embryos were counted at 28 DPI. Embryogenic competence was associated with low IAA and ABA levels in kernels from 0 to 12 DPA, high zeatin to IAA ratios in kernels at 4 DPA, and high cytokinin to auxin ratios in calli. Incompetence in Yaqui 50 may be due to low cytokinin to auxin ratios in kernels at 4 DPA and sharp increases in kernel IAA and/or ABA levels prior to embryo excision (12 DPA). Low temperatures during donor plant growth delayed the rise in IAA and ABA in Yaqui 50 kernels and significantly increased the embryogenic response from both Yaqui 50 and PCYT 10 embryos. It may be possible to increase competence of nearly nonembryogenic wheat lines by growing donor plants in cool conditions, which appear to delay the accumulation of IAA and ABA in kernels.

Involvement of endogenous plant hormones in the effect of mixed nitrogen source on growth and tillering of wheat

Abstract: A Chinese spring wheat (Triticum aestivum L. cv. Yang Mai 158) was grown hydroponically with nitrogen (N) supplied as all ammonium (NH4 +), all nitrate (NC3 ‐), and a mixture (NH4 +‐N:NO3 ‐‐N=30:70) of each form. Wheat plants produced more tiller and more dry matter, and showed a higher shoot/root dry matter ratio when grown with mixed N than with either N form alone. In addition, all‐NH4 +‐grown plants produced more tillers and dry matter as compared to all‐NO3 ‐‐grown plants. Subsequently, endogenous levels of isopentenyladenine and isopentenyladenosine, zeatin and zeatin riboside, dihydrozeatin and dihydrozeatin riboside, indole‐3‐acetic acid (IAA), gibberellin A, and gibberellin A3 (GA1+3) and abscisic acid (ABA) in the shoot and the root was determined by enzyme‐linked immunosorbent assays. It was found that the levels of cytokinin in both the shoot and the root of mixed‐N‐grown plants were higher than those of all‐NO3 ‐‐grown and all‐NH4 +‐grown plant, whereas ABA level was similar among pl...

In vitro stem elongation of sweet pepper in media containing 24-epi-brassinolide

Abstract: In vitro regeneration of sweet pepper (Capsicum annuum L. cvs Jupiter and Pimiento Perfection) has been performed via direct organogenesis. The resulting shoot-buds were placed on media containing 24-epi-brassinolide (EBR) 0.1 μM, a plant steroid lactone, in the presence or absence of zeatin 9.1 μM plus GA3 5.2 μM for further stem elongation. Different responses to these treatments were recorded depending upon the protocols used and the genotypes tested. It appears that EBR does not always act directly on stem elongation but may be an elicitor and/or an enhancer of elongation in concert with endogenous and other exogenously added growth regulators. Elongated shoots were easily rooted with alpha-naphtalenacetic acid 0.5 μM (0.1 mgl-1) and transfered to soil, and following acclimation were taken to maturity in the greenhouse.

Bialaphos stimulates shoot regeneration from hairy roots of snapdragon (Antirrhinum majus L.) transformed by Agrobacterium rhizogenes.

Abstract: Hairy roots of snapdragon (Antirrhinum ma-jus L.: Scrophulariaceae) induced by a wild-type strain of Agrobacterium rhizogenes were cultured on media containing various concentrations of a phosphinothricin-based herbicide, bialaphos, or plant growth regulators (PGRs). Adventitious shoot regeneration from hairy roots was observed with a low frequency (10%) on half-strength Murashige and Skoog medium. Addition of α-naphthalene-acetic acid in combination with 6-benzylaminopurine, thidiazuron, or zeatin to the medium had no effect on shoot regeneration from hairy roots. Although bialaphos at 0.9 mg l–1 or more was toxic to hairy roots, it significantly increased the shoot regeneration frequency up to 56% at 0.5 mg l–1. In contrast, non-transformed roots and leaves regenerated no shoots on media with or without bialaphos. Regenerated shoots detached from host roots readily developed roots on gellan-gum-solidified medium. Regenerated plants were successfully transferred to the greenhouse, but did not produce seed.

A Nicotiana plumbaginifolia protein labeled with an azido cytokinin agonist is a glutathione S‐transferase

Abstract: The mechanisms of reception/transduction of cytokinins still remain largely unknown. We used 1-(2-azido-6-chloropyrid-4-yl)-3-(4-[ 3 H])phenylurea ([ 3 H]azido-CPPU), a new photoaffinity probe to search for cytokinin-binding proteins. A soluble protein that binds phenylurea-type cytokinins has been specifically photolabeled in Nicotiana plumbaginifolia (cv. Viviani line pbH1D) leaf extracts. The protein was purified to homogeneity by affinity chromatography. Its N-terminal amino acid sequence, as well as four internal peptidic sequences are highly homologous with the theta class of the glutathione S-transferase superfamily (GST, EC 2.5.1.18) including Hvoscvamus muticus and Arabidopsis GSTs identified as auxin-binding proteins. The purified N. plumbaginifolia protein also possesses GST enzymatic activity. To test the possible involvement of this GST in the mechanism of action of cytokinin, we studied the binding of tritiated-CPPU to the purified GST in the presence of various compounds, cytokinin agonists, cytokinin antagonists, or inactive molecules. Thidiazuron is a poor competitor, and neither zeatin nor the active optical isomer R-MeBA is able to inhibit the binding of CPPU. There is no correlation between the cytokinin activity and the binding properties of the molecules tested. Our results confirmed that plant GSTs bind different compounds, especially plant hormones but probably have no specific role in the mode of action of cytokinins.

Induced androgenesis in tomato (Lycopersicon esculentum Mill). II. Factors affecting induction of androgenesis

Abstract: The influence on androgenesis of donor plant growth conditions, anther size and developmental stage of the microspore, medium composition and different anther treatments prior to culture was investigated in L. esculentum Mill. cv Roma and its hybrids. Growth conditions of donor plants affected the induction of tomato androgenesis. Anthers isolated from plants grown in the greenhouse during winter at high humidity and in short days possessed higher androgenetic ability than those grown in the field. The physiological state and age of the donor plants also influenced the processes investigated. Regarding the developmental stage of microspores, the period from prophase to telophase II is optimal for tomato anther implantation. More then 20 culture media were tested. Two, based on Murashige and Skoog medium were selected as most favourable for callus induction, organogenesis and regeneration. The effect on callus induction of 2ip in combination with indole-3-acetic acid (IAA) was greater than that of zeatin and IAA. Zeatin promoted entire plant regeneration. A highly significant interaction between genotype and medium was observed. Temperature and gamma ray treatments of anthers enhanced callus production, shoot formation and plant regeneration. Treatments at 4 °C (48 h) and 10 °C (9 days) stimulated these processes. Combined treatment of anthers with 4 Gy and 10 °C for 9 days was the most efficient.

Plant regeneration via somatic embryogenesis, and transient gene expression in sweet potato protoplasts.

Abstract: A method for regenerating plants from petiole protoplasts of the in vitro-raised sweet potato cultivar Jewel is described. Protoplast yields of 3.0–5.0×106 were obtained following 4–6 h digestion of 1- to 2-cm petioles (1 g fresh weight) with 1% Cellulase-R10, 2% Macerozyme-R10, and 0.3% Pectolyase Y-23 in a washing solution with 9% mannitol. A plating density of 105 protoplasts/ml was optimal for subsequent division. An initial division frequency of 12–15% was obtained in liquid or agarose-solidified KP8 culture medium supplemented with 2,4-dichlorophenoxyacetic acid (2,4-D) (0.9 μm), and zeatin (2.3 μm). Colonies consisting of 100–200 cells were formed after 4 weeks in the dark at 24±2°C. The frequency of colony formation was improved by the gradual addition of fresh liquid KP8 medium of lower osmoticum. Protocalli (1–2 mm in diameter) were formed after an additional 4–6 weeks under continuous illumination and regular dilution with fresh culture medium. Morphogenic callus formed globular and heart-shaped embryos that developed into cotyledon stage embryos, following transfer of calli onto medium containing 2,4-D (11.3 μm) and benzylaminopurine (2.2 μm). Subsequently, embryo conversion to plantlets was obtained on basal medium with 2% sucrose and 3.5 μm gibberellic acid. Regenerated plantlets were successfully transplanted in soil. Mature plants appeared phenotypically normal. The same petiole protoplast populations showed transient expression of the gusA gene introduced using electroporation.

Plant-derived smoke solutions stimulate the growth of Lycopersicon esculentum roots in vitro

Abstract: Aqueous extracts of smoke, derived from Themeda triandra, a fire-climax grass, and Passerina vulgaris, a fynbos plant, stimulated the growth of primary root sections of tomato roots in suspension culture. The optimal dilution for both extracts was 1:2000. Several of the fractions obtained from TLC separation of the Themeda and the Passerina extracts significantly promoted primary root growth. The auxins naphthaleneacetic acid (NAA), indolebutyric acid (IBA) and indoleacetic acid (IAA) were found to stimulate the growth of the primary root axis, with IAA and NAA significantly promoting lateral root number. Similarly, the naturally occurring cytokinins, zeatin and its derivatives (zeatin-O-glucoside; dihydrozeatin and zeatin riboside) stimulated primary root length. Zeatin and dihydrozeatin promoted secondary root growth, but only at very low concentrations.

Postharvest changes in endogenous cytokinins and cytokinin efficacy in potato tubers in relation to bud endodormancy

Abstract: Using an indirect enzyme-linked immunosorbent assay (ELISA), the effects of postharvest storage duration and temperature on endogenous cytokinins in potato (Solanum tuberosum L. cv. Russet Burbank) tuber apical bud tissues in relation to endodormancy status were determined. Following fractionation by HPLC, a total of eight cytokinins were detected and these were: zeatin riboside-5′-monophosphate (ZRMP), zeatin-O-glucoside (ZOG), zeatin (Z), zeatin riboside (ZR), isopentenyl adenosine-5′-monophosphate (IPMP), isopentenyl adenine-9-glucoside (IP-9-G), isopentenyl adenine (IP) and isopentenyl adenosine (IPA). Regardless of postharvest storage temperature or endodormancy status, IP-9-G was the most abundant cytokinin detected while ZRMP and ZOG were the least abundant ones. In tubers preincubated at a growth-permissive temperature (20°C) prior to extraction, the loss of endodormancy was preceded by significant increases in the endogenous levels of Z, ZR, IPMP and IP-9-G. When stored continuously at a growth-inhibiting temperature (3°C), significant increases in ZR, IP-9-G and IP + IPA were observed. The total content of cytokinins increased by over 7-fold during postharvest storage and this increase was a result of de novo biosynthesis. Dose-response studies using IPA and ZR demonstrated a time-dependent increase in apparent cytokinin sensitivity during postharvest storage. With the exception of IP-9-G, injection of any of these endogenous cytokinins resulted in the rapid and complete termination of tuber endodormancy. The significance of these results with respect to endodormancy regulation and the possible mechanisms controlling cytokinin levels in potato tubers are discussed.

Changes in selected plant growth regulators during germination in sorghum

Abstract: The technique of radioimmunoassay following sample resolution by HPLC was used to assay the amounts of the cytokinins zeatin (Z), zeatin riboside (ZR) and isopentenyladenine (IPA), the combined amounts of gibberellins1+3 (GA1+3), and the amounts of indole acetic acid (IAA) and abscisic acid (ABA) during germination in grains of sorghum. Concentrations of GA1+3 were low throughout germination and did not appear to be related to the time of germination. In the mature, non-germinated grain, the concentration of each of the other plant growth regulators was much higher in the smaller component comprised of the embryonic axis and scutellum than in the much larger endosperm tissue. During the germination period studied (64 h), these concentrations declined, with a peak in the amount of the cytokinin IPA and a small peak in Z+ZR (24 h) in the embryo following the first visible signs of root protrusion and coincident with a large enhancement in amylase activity. The high concentration of ABA in the embryo tissue prior to germination was noteworthy. It is suggested that the interaction of ABA and the cytokinins IPA and Z+ZR may play a significant role in controlling sorghum germination.

Improved Callus Quality and Prolonged Regenerability in Model and Recalcitrant Barley (Hordeum vulgare L.) Cultivars

Abstract: In vitro performance of immature embryo-derived callus of two barley cultivars, the amenable cultivar, Golden Promise (GP) and the recalcitrant commercial cultivar, Galena (GL), was tested on fourteen media containing combinations of two auxins, dicamba and 2, 4-dichlorophenoxyacetic acid (2, 4-D) and two cytokinins, 6-benzylaminopurine (BAP) and zeatin. Generalizations for both cultivars include the fact that callus-induction frequencies on dicamba and 2, 4-D alone and dicamba plus zeatin were nearly 100%. Qualitative appearance for both cultivars was nearly identical on comparable media but markedly better on BAP-containing media. The addition of zeatin with either auxin supported vigorous growth due to the proliferation of nonregenerable callus; the presence of BAP produced higher quality callus although it inhibited the relative growth rate. GP calli grown on 2, 4-D plus 0.01mg/L BAP regenerated the largest number of green shoots at most time points relative to other media, while GL tissue on 2, 4-D plus 0.1mg/L BAP yielded the most green shoots at all but one time point. Over time regenerability was lost more rapidly in GL than GP except on 2, 4-D plus BAP media; GL had a higher propensity toward albinism than GP. In both cultivars, the use of 2, 4-D and BAP yielded tissue that proliferated for prolonged periods in a regenerable state.

In vitro induction of multiple shoots and plant regeneration in vigna

Abstract: Cotyledonary nodes, excised cotyledons, and hypocotyl segments of six varieties ofVigna mungo andV. radiata have been tested for their morphogenic potential on media containing a range of hormonal combinations including benzyladenine, kinetin, thidiazuron (TDZ), and zeatin. Multiple shoots developed on cotyledonary node explants in all varieties tested on basal medium containing cytokinin. Presence of both the cotyledons, either full or half, resulted in a maximum number of shoots produced. Shoot bud regeneration was achieved via meristem formation on excised cotyledons on Murashige-skoog basal medium with B5 vitamins supplemented with TDZ. Mature plants had normal phenotypes.V. mungo var. PS1 andV. radiata var. Pusa 105 were found to be the most responsive varieties for shoot regneration. The histology ofin vitro organogenesis was studied.

The effect of selected plant hormones on in vitro proliferation of hyphae of Glomus fistulosum

Abstract: Effects of N6-benzyladenine, kinetin, zeatin, N6-benzyladenosine, kinetin riboside, zeatin riboside, jasmonic acid, indole-3-acetic acid, indole-3-butyric acid, indole-3-propionic acid, abscisic acid and gibberellic acid on proliferation of hyphae of arbuscular mycorrhizal (AM) fungus Glomus fistulosum were studied under axenic conditions in vitro. The growth of intraradical hyphae of G. fistulosum was fully suppressed by 30 µM indole-3-acetic acid, but a perceptible decrease in the proliferation of the hyphae was observed already at 3 µM. Because such concentration is near the concentrations common in root tissues in vivo, the effect may be biologically significant. Similar effect was also observed for Glomus mosseae. Inhibitory effects of abscisic acid and cytokinins occurred only at very high, non-physiological concentrations. Ribosylated cytokinins showed stronger inhibition effects than their non-ribosylated counterparts. No stimulation of proliferation of hyphae by any plant hormone tested was observed.

In vitro development of maize immature embryos: a tool for embryogenesis analysis

Abstract: During monocot embryo development, the zygote goes through a proembryo stage characterized by a radial symmetry and later becomes a true embryo with a bilateral symmetry. In order to determine culture conditions for immature embryonic stages, proembryos and embryos were isolated from controlled pollinated maize plants and developed in vitro. Precise culture conditions were determined for each type of explant: a monolayer system for embryos using NBM medium enriched with maltose (0.25 M) but without hormones, and a bilayer system for proembryo stages using N6 medium supplemented with maltose (0.35 M) and zeatin (3 mM). Morphological, cytological, and in situ hybridization analysis have shown that the resulting embryos (stages 1-2), developed in vitro, were similar to those formed in vivo and subsequently gave rise to fertile plants. This work demonstrates that successful embryo differentiation is dependent on specific parameters including the genotype, the nature of the carbon source, the type and concentration of hormones used and orientation of the embryos on the medium. The potential use of these results for embryo rescue and mutant analysis are discussed.

Plant regeneration from anther culture in Canadian cultivars of flax (Linum usitatissimum L.)

Abstract: The effect of culture of anthers at 35 °C for one to four days prior to culture at 25 °C in darkness, genotype, anther orientation on callus induction and shoot regeneration in anther culture of flax was investigated The influence of type and concentrations of cytokinins in the regeneration medium on shoot regeneration was also investigated The results suggested that culture of anthers at 35 °C prior to continuous culture at 25 °C in darkness did not significantly improve the percentage of anthers producing calli However, culture of anthers at 35 °C for one day significantly increased the overall efficiency of regeneration compared to no culture temperature treatment Genotypic effects were significant for the percentage of anthers producing calli and the overall efficiency of regeneration Anther orientation showed no significant differences The regeneration medium containing 45 μM zeatin had significantly higher percentage of calli forming shoots than the same basal medium containing 001 μM TDZ The importance of these findings for flax breeding was discussed

Cytokinins in the vascular saps of Ricinus communis

Abstract: Roots are recognised as the major sites of cytokinin synthesis and shoots receive a continuous supply of cytokinins from the roots. Although reports are available on the xylem mobility of putative free bases and their ribosides, relatively few studies on the phloem mobility of cytokinins have been reported. The origin of phloem-mobile cytokinins is uncertain but there is evidence which implicates a recirculation from the root source. This study is the first report in which zeatin and zeatin riboside from the root pressure exudate and phloem sap of Ricinus have been identified by full-scan GC-MS and quantified by GC-MS selective-ion-monitoring. In this study, the concentration of cytokinins in root pressure exudate was similar, but lower, and in the phloem sap higher than that reported previously. The concentration of cytokinins quantified in the phloem sap confirms their transport in the sieve tubes. The relatively high concentration of zeatin riboside detected in the root pressure exudate and of zeatin detected in the phloem sap indicate a possible vascular recirculation of these hormones.

In Vitro Culture of Rudimentary Embryos of Ilex paraguariensis: Responses to Exogenous Cytokinins

Abstract: The effects of benzyladenine (BAP), kinetin (KIN), zeatin (ZEA), isopentenyladenine (2iP), and thidiazuron (TDZ) were studied on in vitro growth of rudimentary embryos of Ilex paraguariensis St. Hil. Heart stage zygotic embryos were removed from seeds of immature, light green fruits and cultured aseptically on quarter-strength Murashige and Skoog medium containing 3% sucrose, 0.65% agar, and supplemented with or without three concentrations of BAP, KIN, ZEA, 2iP, or TDZ. Cultures were incubated in darkness at 27 ± 2°C. Media containing 4.4 × 10−6m BAP, 4.6 × 10−6m KIN, or 4.9 × 10−6m 2iP were totally ineffective in inducing embryo growth after culture for 28 days. However, lower concentrations of these compounds (4.4 × 10−8m BAP, 4.6 × 10−8m KIN, 4.5 × 10−8m ZEA, or 4.9 × 10−8m 2iP) promoted embryo growth. TDZ at 9.9 × 10−9m, 9.9 × 10−8m, or 9.9 × 10−7m induced embryo growth at similar rates. The maximum percentage of embryos converted to seedlings was achieved when the medium was supplemented with 4.5 × 10−7m ZEA.

Adventitious shoot production from strips of stem in the Dutch elm hybrid ‘Commelin’: plantlet regeneration and neomycin sensitivity

Abstract: The regenerative ability of small strips of stem of the Dutch elm hybrid ‘Commelin’ was tested as well as its sensitivity to neomycins Cambium explants (1 mm thick), were excised from woody stems collected in the field Up to 20 buds/explant were induced within 2–3 weeks giving 2–5 rootable shoots/explant after 5–6 weeks Shoot excision every week from week three improved the yield up to 7 shoots per explant Fourteen and 29 μM GA3 promoted shoot growth Cytokinins (1 μM zeatin or 5 μM BA or 005 μM TDZ) completely inhibited shoot production and promoted callus formation Kanamycin and paromomycin at between 240 and 360 μM inhibited shoot formation as did geneticin at 80 μM The shoot-forming ability of the explants was high from leaf fall in the autumn to the spring flush, but could be maintained up to September by using cold storage (5–7 °C) Ninety-six percent of the shoots rooted with 05 μM IBA and were successfully acclimatized despite having a large basal callus

Adventitious shoot regeneration from leaf explants of an African clone of cassava (Manihot esculenta Crantz) and analysis of the conformity of regenerated plants

Abstract: A protocol for regeneration of adventitious shoots from immature leaf lobes from in vitro plants of cassava has been developed. Induction occurred in the presence of 2,4-D for ten days which was followed by transfer onto the regeneration medium containing 23 μM zeatin. Induction for more than 10 days in 2,4-D resulted in reduced regeneration and delayed shoot formation. A friable callus developed after a longer induction phase. A shorter induction resulted in the formation of foliar structures which did not develop further. Following subculture calluses produced shoots with improved frequency: 1.0 shoot/explant after 4 subcultures and 1.8 shoots/callus after 14 subcultures. When transplanted into soil, the regenerated plants were apparently normal and similar to the stock plants. A sample of 203 regenerants was examined for isozymes and DNA content using flow cytometry. Glutamate oxaloacetate transaminase (GOT) banding pattern was identical to that of the stock plants. Small changes were however detected in the phosphoglucomutase (PGM) pattern for 3.4% of regenerated plants, showing an additional band in the fast migration zone. The DNA content of the regenerated plants was homogeneous and was similar to that of the stock plants. The ploidy level was unchanged (2n = 36 chromosomes).

The response of dodder {Cuscuta spp.) seedlings to phytohormones under various light regimes

Abstract: Summary Phytohormones were screened for their effects on induction of coiling and prehaustoria in de-etiolated excised dodder seedlings under different light treatments. Zeatin stimulated coiling and the formation of prehaustoria under all light tested, even in darkness. A synergistic effect was observed with zeatin and far-red light (700–800 nm) but not with red light (600–700 nm) on the formation of prehaustoria. Application of indole-3acetic acid inhibited zeatin-induced coiling and prehaustoria development under blue (400–500 nm) and a mixture of red plus far-red light, but not in blue plus far-red light. Ethylene had no effect on coiling and prehaustoria development. Observations suggest that zeatin-induced coiling and prehaustoria development may be mediated by phytochrome.