Showing papers on "Zeatin published in 1997"
TL;DR: The role of cytokinins as a long-range root-to-shoot signal in correlative control of apical dominance and sequential leaf senescence of tobacco is questioned, and the assumption that this hormone is relevant to paracrine signaling is supported.
Abstract: This study investigated whether an increased production of the plant hormone cytokinin in roots, the main site of its synthesis and putative signaling organ, can influence developmental events, such as growth of axillary shoot meristems or leaf senescence, in the plant shoot. To this end, transgenic tobacco plants (Nicotiana tabacum L.) were generated that conditionally overproduce cytokinins. These plants harbour the ipt gene under the transcriptional control of a modified 35S promoter that is repressed in plants with high titers of tetracycline repressor protein. De-repression of transcription led to a rapid more than 50-fold increase of hormone concentration. The time course of changes in the steady-state levels of 16 different cytokinin metabolites, as a consequence of IPT enzyme activity, was monitored in different plant tissues. Zeatin riboside was the first and most dramatically increased product; zeatin, dihydrozeatin and glucosides accumulated later. The consequences of enhanced cytokinin synthesis remained mainly restricted to the site of hormone production. For example, de-repression of ipt gene transcription in lateral buds caused the growth of single buds only at the site of tetracycline application. In reciprocal grafts of transgenic plants with wild-type plants, no biological cytokinin effects, i.e. growth of lateral shoot meristems or sequential leaf senescence, were observed in the non-transgenic plant part. Also, the increase in steady-state levels of cytokinins remained restricted mainly to the transgenic part, despite a specific increase of the zeatin riboside concentration in the transpiration stream. These results question the role of cytokinins as a long-range root-to-shoot signal in correlative control of apical dominance and sequential leaf senescence of tobacco, and support the assumption that this hormone is relevant to paracrine signaling.
322 citations
TL;DR: This review attempts to put into context what is known about 9-alkyl-BAs and compares their metabolism in regard to the practical use of cytokinins in agriculture and biotechnology.
Abstract: After the discovery of kinetin (Miller et al. 1956, J. Am. Chem. Soc. 78: 1345–1350) there was a flurry of syntheses that led to the finding of 6-benzylaminopurine (BA), an active and easily obtainable cytokinin. Much research into cytokinin physiology was subsequently done with this substance. Further, the isolation and unequivocal identification of natural BA and the high biological activity of its meta-hydroxylated analogues stimulated the search for other natural aromatic cytokinins. Screening was accomplished by ELISA of HPLC fractions using antisera against ortho- and meta-hydroxybenzyladenosine. Subsequent isolation and decisive identification by mass spectrometry led to discovery of a broad spectrum of endogenous plant growth substances structurally similar to a highly active compound, meta-topolin (6-[3-hydroxybenzyl-amino]purine), and to its less active analogue, ortho-topolin (6-[2-hydroxybenzyl-amino]purine). The structures of such aromatic cytokinins suggest considerably different biosynthetic pathways from that of zeatin and related isoprenoid cytokinins. From a physiological viewpoint, aromatic cytokinin metabolism can be classified under four main headings analogous to isoprenoid cytokinins: interconversion, hydroxylation, conjugation, and oxidative degradation. This review attempts to put into context what is known about 9-alkyl-BAs and compares their metabolism in regard to the practical use of cytokinins in agriculture and biotechnology. The recently discovered unusual specificity of additionally C2,N9-disubstituted aromatic cytokinins toward cell cycle kinases, suggests that these cytokinin-derived growth regulators may selectively inhibit certain steps of the cell cycle. The functional overlap of the aromatic cytokinins with those of their isoprenoid counterparts and cytokinin inhibitors, in relation to growth and developmental processes in plants, has yet to be determined.
225 citations
TL;DR: This is the first detailed report of CK levels in buds themselves during release of apical dominance, and it is suggested that CKs may be part of an endogenous signal involved in lateral bud growth stimulation following shoot decapitation.
Abstract: We examined the role of cytokinins (CKs) in release of apical dominance in lateral buds of chickpea (Cicer arietinum L.). Shoot decapitation or application of CKs (benzyladenine, zeatin or dihydrozeatin) stimulated rapid bud growth. Time-lapse video recording revealed growth initiation within 2 h of application of 200 pmol benzyladenine or within 3 h of decapitation. Endogenous CK content in buds changed little in the first 2 h after shoot decapitation, but significantly increased by 6 h, somewhat later than the initiation of bud growth. The main elevated CK was zeatin riboside, whose content per bud increased 7-fold by 6 h and 25-fold by 24 h. Lesser changes were found in amounts of zeatin and isopentenyl adenine CKs. We have yet to distinguish whether these CKs are imported from the roots via the xylem stream or are synthesised in situ in the buds, but CKs may be part of an endogenous signal involved in lateral bud growth stimulation following shoot decapitation. To our knowledge, this is the first detailed report of CK levels in buds themselves during release of apical dominance.
116 citations
TL;DR: A natural free radical scavenger, ascorbic acid (AsA) shows both counteractive and enhancing effects on JA‐inducible phytoalexin production, depending on its concentration, which suggests that active oxygen species (AOS) may play important roles in phy toalex in production by JA in rice leaves.
94 citations
TL;DR: Plant regeneration by somatic embryogenesis was attempted with diploid and triploid bananas and showed that the embryogenic process involves a sequence of similar events for both species.
Abstract: Plant regeneration by somatic embryogenesis was attempted with diploid (Musa acuminata ssp. malaccensis) and triploid ('Grand Nain') bananas. Explants inoculated in vitro were, respectively, immature zygotic embryos and male flower bud primordia. An histological study showed that the embryogenic process involves a sequence of similar events for both species. A yellow-green compact callus was initiated, which consisted of an actively dividing meristematic zone surrounded by several layers of starchy cells. A white and friable callus, characterized by the presence of proembryonic cells, bicellular proembryos and proembryonal masses in its periphery gradually appeared, which finally gave rise to somatic embryos from which plants were recovered. Induction media contained 2,4-D (and also NAA and IAA for the triploid); zeatin and kinetin were necessary for embryo maturation and 6-BA and IAA were used for germination.
84 citations
TL;DR: It is suggested that urea may be an important source of nitrogen often found inside the tank of V. philippocoburgii, while urea and NH 4 + shifted this ratio in favour of cytokinins, thus apparently inhibiting root development in both species.
Abstract: The long-term effects of different nitrogen sources on the endogenous IAA and cytokinin levels in two bromeliad species were investigated. In nature, Vriesea philippocoburgii is a tank-forming epiphytic bromeliad which uses the tank water reservoir as a substitute for soil, whereas Tillandsia pohliana is a tankless atmospheric epiphytic species. A culture was established from seeds germinated in aseptic condictions, and the plantlets were grown for 6 months in a modified Knudson medium to which was added 8 mol m -3 of nitrogen in the form of NO 3 - NH4 + or urea. The hormonal contents of the bromeliad shoots were determined by means of high-performance liquid chromatography (HPLC), coupled to an enzyme-linked immunosorbent assay (ELISA) for indole-3-acetic acid (IAA), isopentenyladenine (iP), isopentenyladenosine ([9R]iP), zeatin (Z) and zeatin riboside ([9R]Z). Nitrogen supplied in the form of urea gave the highest values of fresh and dry weights for both species, and this was positively correlated to IAA levels. The cytokinin patterns showed that isopentenyladenosine was the predominant form for both species in all samples. However, urea induced the highest level of this riboside form and also the highest level of total cytokinins for V. philippocoburgii, while NH 4 + had the same effect on the atmospheric species. These results are discussed in terms of the different growth habits of these two species in nature. It is suggested that urea may be an important source of nitrogen often found inside the tank of V. philippocoburgii. NO 3 - treatment increased the IAA/Cks balance, mainly for V. philippocoburgii, while urea and NH 4 + shifted this ratio in favour of cytokinins, thus apparently inhibiting root development in both species.
58 citations
TL;DR: Stem cuttings were the most suitable explants for multiple-shoot proliferation, and when cultured on a woody plant medium containing 2.5 μM BA produced axillary shoots which branched repeatedly, yielding an average of 27 shoots per explant after 6 weeks in culture.
Abstract: Various factors that affect culture establishment, shoot growth, proliferation and rooting ofIxora coccinea L., a woody shrub, were studied. Stem cuttings (decapitated shoot, three nodes) were the most suitable explants for multiple-shoot proliferation, and when cultured on a woody plant medium (WPM) containing 2.5 μM BA produced axillary shoots which branched repeatedly, yielding an average of 27 shoots per explant after 6 weeks in culture. Kinetin, 2-iP, zeatin and thidiazuron all induced multiple-shoot formation, but were less effective than BA. While the presence of IAA in the multiplication medium was detrimental to shoot proliferation, shoot growth was not affected by IAA. The production of large amounts of basal callus and vitrification of shoots were the major problems to be avoided in proliferating shoot cultures. Addition of TIBA to the multiplication medium markedly reduced basal callusing, while sealing the culture vessels with a fluorocarbon polymer (tetrafluoroethyleneperfluoroalkyl vinyl ether) film (Neoflon PFA film) almost completely eliminated vitrification. A reduction in the number of vitrified shoots was also achieved with AVG treatment. Following this protocol of using BA-supplemented WPM and Neoflon film, it would be possible to produce more than 100,000 plants from a single stem cutting in 1 year.
51 citations
TL;DR: Preliminary evaluation in field conditions in Gabon revealed that plants regenerated from cultured protoplasts exhibited a great genetic variability in their growth and tuber formation in particular.
Abstract: The application of new techniques for improvement of sweet potato crops, particularly including the exploitation of somaclonal variation, gene transfer by genetic transformation and somatic hybridization, requires the control of plant regeneration from tissue cultures. Shoots can easily be regenerated from explants of stems, petioles, leaves and roots, while callus cultures do not produce any shoots. The potential of somatic embryogenesis and plant regeneration via embryogenesis was evaluated for 10 cultivars of sweet potato. Protocols for plant regeneration from cultured protoplasts have also been developed. Since mesophyll was resistant to enzyme digestion, fragments of stems and petioles, callus and cell suspensions were used as source of protoplasts of sweet potato. Series of transfers of protoplast-derived calluses, particularly those which had been obtained from in vitro plants, to media containing a high level of zeatin resulted in successful formation of shoots in only two sweet potato cultivars. In addition, the embryogenic potential was irreversibly lost through protoplast culture, since protoplasts isolated from embryogenic cell suspensions developed into non-embryogenic callus. Consequently, an alternative protocol is being successfully developed to improve plant regeneration from cultured protoplasts of sweet potato, involving first root formation from which shoots can then be regenerated. Preliminary evaluation in field conditions in Gabon revealed that plants regenerated from cultured protoplasts exhibited a great genetic variability in their growth and tuber formation in particular.
49 citations
TL;DR: Of the four cytokinins tested (6-benzylaminopurine (BAP), thidiazuron (TDZ), zeatin, and kinetin), BAP induced shoot development most efficiently and was observed after preculture on medium with 5 mg/l BAP followed by transfer to 10 mg/L BAP.
Abstract: Nodes from 3- to 5-week-old in vitro plants of different cassava cultivars were cultured for 2-3 days on solid Murashige and Skoog basal medium supplemented with cytokinin to induce the enlargement of axillary buds. Subculture of these buds on the same medium resulted in multiple shoot formation within 4-6 weeks. Of the four cytokinins tested (6-benzylaminopurine (BAP), thidiazuron (TDZ), zeatin, and kinetin), BAP induced shoot development most efficiently. The best results were obtained with cultivar TMS 30555, in which 63% of the explants each produced at least 25 shoots on medium with 10 mg/l BAP. In cultivars that did not produce shoots, the addition of the surfactant Pluronic F-68 (2% wt/vol) raised the percentage of explants forming at least 5 shoots from 0 to 20-60%. Axillary buds were also used to dissect meristems and test their ability to regenerate into shoots. Shoot formation from meristems of six different cultivars was observed after preculture on medium with 5 mg/l BAP followed by transfer to 10 mg/l BAP.
48 citations
TL;DR: The IAA/ABA and, mainly, the iP-type/Z-type cytokinin ratios were found to be two good indexes of the embryogenic competence of explants, suggesting that the endogenous hormonal balance is a very important factor defining the in vitro potential of hazelnut cotyledons.
Abstract: Endogenous indole-3-acetic acid (IAA), abscisic acid (ABA) and cytokinins [zeatin (Z) zeatin riboside, dihydrozeatin, dihydrozeatin riboside, N6-isopentenyl adenine (iP) and N6-isopentenyladenine riboside] were evaluated in hazelnut (Corylus avellana L.) cotyledons of different developmental stage and genetic source for their somatic embryogenic capacity. There was an inverse correlation between the embryogenic potential of cotyledons and the degree of maturity of zygotic embryos, the first characteristic being associated with iP-type cytokinins and the second with Z-type cytokinins. Although the differences in total cytokinin, ABA and IAA contents between the cotyledons were small, the IAA/ABA and, mainly, the iP-type/Z-type cytokinin ratios were found to be two good indexes of the embryogenic competence of explants, suggesting that the endogenous hormonal balance is a very important factor defining the in vitro potential of hazelnut cotyledons.
47 citations
TL;DR: A system for producing haploid plants from anther cultures was developed for the Asiatic hybrid lily ‘Connecticut King’ and Chromosome counts of root-tip cells of 11 plantlets revealed that five were haploids, two diploids, and four mixoploid, suggesting that at least some plantlets were of gametophytic origin.
Abstract: A system for producing haploid plants from anther cultures was developed for the Asiatic hybrid lily ‘Connecticut King’. Anthers containing microspores at the mid- to late-uninucleate stages were cultured on MS media supplemented with various plant growth regulators. Microspores containing 3 or 4 vegetative-like nuclei were observed 2 to 3 weeks later, and yellowish nodular calluses appeared within dehisced anthers 2 to 3 months after culture. Picloram was superior to 2,4-d for inducing nodular calluses. Anthers from greenhouse-grown plants required higher concentrations of both picloram and cytokinins than those from field-grown plants and most frequently produced nodular calluses (17.6%) on MS medium containing 2 mg 1−1 picloram and 2 mg 1−1 zeatin. The nodular calluses regenerated many bulblets following transfer to MS medium supplemented with 0.1 or 0.5 mg 1−1 picloram and 0.01 mg 1−1 BA, and the bulblets developed into plantlets (bulblets with scaly leaves and roots) after transfer to MS medium containing 0.1 mg 1−1 NAA. Chromosome counts of root-tip cells of 11 plantlets revealed that five were haploids (2n = 12), two diploids (2n = 24), and four mixoploid. This result suggests that at least some plantlets were of gametophytic origin.
01 Jan 1997
TL;DR: The cytokinin peak is followed by a peak in free indole-3-acetic acid (approximately 10 to 15 days after pollination) and is associated with the endosperm cell enlargement and endoreduplication phase.
Abstract: Shortly after pollination, developing cereal grains exhibit significant transient increases in two of the major plant hormones, auxins and cytokinins. A peak in active cytokinins occurs between three to eight days after pollination in all species examined so far. Both zeatin and zeatin riboside concentrations increase by as much as one hundred fold for a period of three days and then decrease equally rapidly. The peak always coincides in time with the peak in endosperm cell division rate, although no causal relationship has been demonstrated between the two events. The enzyme cytokinin oxidase increases shortly after the increase in active cytokinins and is responsible for reducing cytokinins back to basal levels. The cytokinin peak is followed by a peak in free indole-3-acetic acid (approximately 10 to 15 days after pollination) and is associated with the endosperm cell enlargement and endoreduplication phase. The high levels of free IAA are not destroyed but are converted to various conjugates which probably supply the developing seedling with a source of free IAA.
TL;DR: The enhancement of cytokinin oxidase activity after BA treatment in both tissue lines was correlated with the content of preferred substrate of the enzyme, N6-(Δ2-isopentenyl)adenosine.
Abstract: There are indications that the cytokinin content in transgenic tissues expressing the cytokinin biosynthetic ipt gene is under metabolic control, which prevents the accumulation of cytokinins to lethal levels. The objective of this study was to investigate the relationships between the content of endogenous cytokinins and the activity of cytokinin oxidase (which is believed to be a copper-containing amine oxidase, EC 1.4.3.6.) in ipt transgenic tobacco callus. In addition, the effect of exogenously applied N-benzyladenine (BA) on this relationship was examined. Endogenous cytokinin concentrations were measured in callus of Nicotiana tabacum L. cv. Petit Havana SRI transformed with the ipt of Agrobacterium tumefaciens under the control of a light-inducible promoter and in non-transformed tissue using LC-tandem mass spectrometry. The activity of cytokinin oxidase was estimated by measuring the conversion of [2,8-3H]N6-(Δ2-isopentenyl)adenine to [3H]adenine by enzyme preparations in vitro.
The 14-day-old ipt-transformed callus contained a 25-fold higher amount of cytokinins as compared to the non-transformed tissue. Mainly zeatin- and dihydrozeatin-types of cytokinins (free bases, ribosides, nucleotides and O-glucosides) accumulated in the ipt transgenic tissue. The cytokinin pool of both ipt-transformed and non-transformed tissues consisted predominantly of cytokinins that are either resistant to cytokinin oxidase attack (nucleotides and O-glucosides of cytokinins and cytokinins bearing N6-saturated side chain) or have a low affinity for the enzyme (zeatin and its riboside). The former represented 71.6 and 74.8% and the latter 27.7 and 24.4% of the pool of endogenous cytokinins in ipt-transformed and non-transformed tissues, respectively. Enzyme preparations from ipt-transformed tissue exhibited 1.5-fold higher cytokinin oxidase activity compared with that observed in control tissues.
Application of exogenous BA affected the total levels of cytokinins of the two tissue lines in different ways. The cytokinin content increased by 1.7- and 1.5-fold in ipt-transformed tissues 6 and 12 h after BA application, respectively, while it declined in the non-transformed control by 1.6- to 2.0-fold between 3 and 12 h after BA application. The increase in cytokinin content in the ipt callus is due to an increase of zeatin- and dihydrozeatin-type cytokinins (nucleotides, ribosides and free bases) leading to an enhanced accumulation of O-glucosides after 12 h. Following BA treatment, the cytokinin oxidase activity increased up to 1.8-fold in ipt-transformed and 1.6-fold in non-transformed tissues. The levels of isopentenyl-type cytokinins were near the detection limit; however, the enhancement of cytokinin oxidase activity after BA treatment in both tissue lines was correlated with the content of preferred substrate of the enzyme, N6-(Δ2-isopentenyl)adenosine.
TL;DR: In this paper, the in vitro propagation of wild pear (Pyrus syrica) was studied and the root height decreased to 1.8-1.6 cm and 1.3 cm with benzyl adenine.
TL;DR: The influence of different auxins and cytokinins on somatic embryogenesis was investigated and 2,4-dichlorophenoxy acetic acid was the most effective and resulted in the highest frequency of responding cultures and highest average number of somatic embryo per responding cultures.
Abstract: Somatic embryos were induced from hypocotyl-derived callus of sesame (Sesamum indicum Var TMV 6) The influence of different auxins and cytokinins on somatic embryogenesis was investigated Among the different auxins tested, 2,4-dichlorophenoxy acetic acid was the most effective and resulted in the highest frequency of responding cultures and highest average number of somatic embryo per responding cultures napthaleneacetic acid, indoleacetic acid, indolebutyric acid and 2,4,5-trichlorophenoxypropionic acid were also effective for embryogenesis, but 2,4,5-trichorophenoxyacetic acid and napthoxyacetic acid were not beneficial The combined effect of cytokinins with 2,4-d was also studied Among the four cytokinins tested, 22 chμM benzyladenine with 136 chμM 2,4-d slightly enhanced embryogenic efficiency; while kinetin, zeatin, 6-γ-γ-dimethylallylaminopurine enhanced the frequency of responding cultures There was a decrease in the number of somatic embryos per culture in the presence of all cytokinins
TL;DR: High-frequency somatic embryogenesis was achieved from an embryogenic cell suspension culture of Acanthopanax koreanum Nakai and Cytokinin treatment suppressed the normal growth of embryos, but stimulated secondary somatic embryos from the surfaces of primary embryos.
Abstract: High-frequency somatic embryogenesis was achieved from an embryogenic cell suspension culture of Acanthopanax koreanum Nakai. Stem segments were cultured on Murashige and Skoog (MS) medium containing auxins and cytokinins. Opaque and friable embryogenic callus formed on MS medium with 4.5 µm 2,4-dichlorophenoxyacetic acid (2,4-D) and 2.0 µm kinetin or zeatin, but was highest on medium containing 4.5 µm 2,4-D alone. Embryogenic calli were transferred to MS liquid medium containing 4.5 µm 2,4-D and maintained by subculture at 2-week intervals. Initiation of somatic embryogenesis and development up to the globular stage from embryogenic cell clumps occurred in medium containing 0.45 µm 2,4-D, whereas maturation and germination of somatic embryos occurred in MS medium lacking 2,4-D. Cytokinin treatment suppressed the normal growth of embryos, but stimulated secondary somatic embryogenesis from the surfaces of primary embryos. Plants from somatic embryos were acclimatized in a greenhouse.
TL;DR: The adventitious origin of shoots regenerated from stem explants was confirmed by scanning electron microscopy, and the regeneration procedure was found to be applicable to five other gypsophila cultivars (Perfecta, Golan, Gilboa, Flamingo and Tavor).
Abstract: An efficient adventitious shoot regeneration procedure was developed for Gypsophila paniculata L. Using cultivar Arbel, shoot regeneration from the three upper internodes of the stem was monitored on MS media supplemented with different cytokinins (thidiazuron, benzyladenine, kinetin or zeatin) and an auxin (naphthaleneacetic acid). Thidiazuron was found to be the most efficient cytokinin, with up to 100% of the explants forming shoots, at an average of up to 19 shoots per explant being regenerated. The highest percentage of shoot formation was observed in the stem explants originating from the first internode, with all cytokinins tested. The adventitious origin of shoots regenerated from stem explants was confirmed by scanning electron microscopy. The regeneration procedure was found to be applicable to five other gypsophila cultivars (Perfecta, Golan, Gilboa, Flamingo and Tavor). Regenerating plants were successfully transferred to soil, and did not differ in flower color, size or shape from standard vegetatively propagated plants derived from cuttings.
TL;DR: A modified culture protocol has been developed for the induction of somatic embryogenesis in Azadirachta indica (neem) and the embryo production was found to improve more than 2 fold by adding 0.2 mg l−1 zeatin to the medium.
Abstract: A modified culture protocol has been developed for the induction of somatic embryogenesis in Azadirachta indica (neem). Embryogenic calluses were initiated from cotyledons or hypocotyls using a Murashige and Skoog (MS) agar medium supplemented with 0.5 mg l−1 α-napthaleneacetic acid (NAA), 1 mg l−1 6-benzylaminopurine (BA), 1 g l−1 casein hydrolysate, and 50 g l−1 sucrose. The calluses, when transferred to a liquid medium similar to the agar medium but with NAA replaced by 0.5 mg l−1 indole-3-acetic acid (IAA), formed globular structures which further developed a rudimentary root, after 4 to 5 weeks incubation. Subsequently, these highly differentiated tissues when transferred into a hormone-free MS medium containing 1 g l−1 casein hydrolysate and 50 g l−1 sucrose, active embryo masses started to appear after 1 to 2 weeks. The embryo production was found to improve more than 2 fold by adding 0.2 mg l−1 zeatin to the medium.
TL;DR: Begoniaxelatiorplantlets which regenerated from leaf disk callus showed variations in plant morphology, number of flowers per plant, and flower size, and micropropagation of selected somaclones having the desirable trait of high number of Flowers per plant was stable in the MV2 and MV3 generations.
Abstract: Begonia x
elatior
plantlets which regenerated from leaf disk callus showed variations in plant morphology, number of flowers per plant, and flower size. Variations in flowering period, number of flowers per plant, and flower morphology were observed in
Saintpaulia ionantha
L. plants directly regenerated from leaf disk explants. The cytokinins, benzylaminopurine and zeatin, tested in the culture medium did not affect the basic plant characteristics including flower colour which remained stable in both species. Micropropagation of selected somaclones having the desirable trait of high number of flowers per plant was stable in the MV2 and MV3 generations.
TL;DR: It is concluded that the endogenous zeatin-like cytokinin level (free and ribosylated forms) can be considered as a reliable marker for the recovery of in vitro shoot and root organogenesis after rejuvenating treatments in rubber-tree clones.
Abstract: The endogenous levels of isopentenyladenine, isopentenyladenosine, zeatin and zeatin riboside and the ability forin vitro axillary shoot organogenesis and rhizogenesis were compared between mature and rejuvenated clones ofHevea brasiliensis (Mull. Arg.). Enhancement of thein vitro organogenesis ability of rubber-tree clones following somatic embryogenesis or repeated grafting onto juvenile rootstocks was accompanied by an increase of zeatin riboside levels in shoots used as starting material forin vitro micropropagation. Furthermore, the zeatin level, inin vitro shoots of clones treated byin vitro micrografting, and consequently capable of axillary shoot and root organogenesis, was higher than inin vitro shoots of non treated mature material incapable of in vitro organogenesis. We conclude that the endogenous zeatin-like cytokinin level (free and ribosylated forms) can be considered as a reliable marker for the recovery ofin vitro shoot and root organogenesis after rejuvenating treatments in rubber-tree clones.
TL;DR: It was found that explants grown on a half-strength Anderson's medium with 87.6 mM sucrose generally had better shoot proliferation rate and shoot quality than at higher ionic strength.
Abstract: Shoot-tip explants of evergreen azalea cv Fuchsia grown on Anderson's medium and containing different cytokinins produced the highest proliferation rate on a medium containing thidiazuron (TDZ) TDZ concentrations ranging from 023 to 23 μM resulted in both good bud-break rate (4 to 5) and shoot quality (> 05 cm in length) Adding 23 μM zeatin to Anderson's medium containing 023 or 23 μM TDZ increased the number of axillary shoots/explant However, increasing the zeatin concentration to 46 μM resulted in a reduced shoot proliferation rate A medium containing 115 μM TDZ and 23 μM zeatin resulted in an 18-fold increase for 'Fuchsia' and a 9-fold increase for 'Hino Crimson' after 6 weeks of culture It was found that explants grown on a half-strength Anderson's medium with 876 mM sucrose generally had better shoot proliferation rate and shoot quality than at higher ionic strength
TL;DR: Findings indicate that both IAA and cytokinins are involved in tuber initiation regardless of light quality, while cytokin ins appear to stimulate the assimilate flow to developing storage tissue.
TL;DR: The incidence of hyperhydration and chlorotic foliage was severe, especially for ohelo, in all treatments with supplemental FeEDTA, and exogenous zeatin riboside accumulated in foliage by the end of a grow...
Abstract: Two Vaccinium genotypes growing in vitro (V. pahalae, ohelo, and V. myrtillus, bilberry) were examined under variable iron (Fe) and growth regulator regimes in order to elucidate the cause(s) of abnormal tissue formation. Two Fe sources (200, 300, and 400 μM Fe from FeEDTA and 150, 200 and 250 μM Fe from a combination of 100 μM FeEDTA supplemented with FeEDDHA) were used in combination with 12.3 μM 2iP (N‐[3‐methyl‐2‐butenyl]‐1‐H‐purine‐6‐amine), 18.2 μM zeatin, or 11.4 μM zeatin riboside. No hyperhydration and only trace chlorosis occurred in 2iP treatments, but growth was substandard, as reflected by significantly lower fresh and dry mass yields from shoots harvested after eight weeks. Although zeatin or zeatin riboside treatments induced greater shoot proliferation, the incidence of hyperhydration and chlorotic foliage was severe, especially for ohelo, in all treatments with supplemental FeEDTA. In FeEDTA‐supplemented media, exogenous zeatin riboside accumulated in foliage by the end of a grow...
TL;DR: Concomitant changes in the accumulation pattern of ajmalicine and the 28 kD polypeptide suggest that the latter can play a (direct or indirect) regulatory role in the indole alkaloid pathway of periwinkle cells.
TL;DR: Zeatin added, to B5 basal medium, supplemented with 1.5 % sucrose and 0.2 µmol indole-3-acetic acid, was the most effective cytokinin on somatic embryogenesis from chickpea immature cotyledons.
Abstract: Studies were conduced to test the effects of various cytokinins on somatic embryogenesis from chickpea (Cicer arietinum L.) immature cotyledons. Zeatin (13.7 µmol) added, to B5 basal medium, supplemented with 1.5 % sucrose and 0.2 µmol indole-3-acetic acid, was the most effective cytokinin. Lobular structures obtained from cotyledons cultures were transferred to B5 basal medium supplemented with gibberellic acid and indole-3-butyric acid at different concentrations. The most effective treatment was B5 medium containing 14.4 µmol gibberellic acid plus 1.0 µmol indole-3-butyric acid in which 42.8 % of lobular structures cultured formed normal somatic embryos. High conversion of embryos into plantlets (61.0–65.2 % embryos regenerated plants) was observed when germinated embryos were placed on plant development medium.
TL;DR: Among the plant growth factors used, cytokinins, zeatin, 6-benzylaminopurine and kinetin were the most effective in promoting embryo maturation and development.
Abstract: Factors responsible for successful rescue of immature embryos of cowpea [Vigna unguiculata (L.) Walp.] and V. vexillata (L.) and for in vitro embryo development were studied. A new basal medium for embryo development in vitro was formulated on the basis of the mineral composition of embryos. Sucrose, fructose and glucose were compared as carbohydrate sources. The highest frequency of embryos developing into plants was obtained with sucrose. Adding casein hydrolysate to the medium increased plant recovery by 30%. Among the plant growth factors used, cytokinins, zeatin, 6-benzylaminopurine and kinetin were the most effective in promoting embryo maturation and development. A method that can routinely ensure high plant recovery from cultured immature cowpea embryos is proposed.
TL;DR: It is concluded that leaf expiants cultured on ZIG medium at all stages of culture were the most effective at shoot production.
Abstract: A previously published medium has been found to be effective for plant regeneration from leaf expiants ofSolanum tuberosum cv. Katahdin. A number of combinations of thidiazuron and naphthaleneacetic acid, along with a medium previously published for shoot regeneration from protoplast-derived calli ofSolanum phureja, which contained zeatin, indoleacetic acid and gibberellic acid (ZIG), were tested for callus induction, and all calli were transferred to ZIG for shoot induction. We conclude that leaf expiants cultured on ZIG medium at all stages of culture were the most effective at shoot production. A mean of over six shoots were produced per expiant after four months in culture.
TL;DR: It is suggested that in longan, the cytokinins that are translocated to the shoots are accumulated in the buds at the dormant stage, and that later there is a considerable increase in free cytokinin during flower bud initiation, leading to the promotion of flower bud development.
Abstract: The presence of endogenous cytokinins were detected in the terminal buds of longan (Euphoria longana Lam.) after purification by ion exchange and Sephadex LH-20 chromatography, and bioassay, enzymic degradation, high-performance liquid chromatography and gas chromatography-mass spectrometry. Permethylated derivatives of two highly active cytokinin glucoside compounds from dormant buds were: 6-(4-O-β-D-glucosyl-3-methyl-but-2-enylamino) purine (zeatin-O-glucoside) and 9-β-D-ribofuranosyl-6-(4-hydroxy-3-methyl-but-2-enylamino) purine (zeatin riboside-O-glucoside). Simultaneously, four active cytokinins from buds at the stages of leaf flush and flower bud initiation were identified as 6-(4-hydroxy-3-methyl-but-trans-2-enylamino) purine (zeatin), zeatin-9-β-D-ribofuranosylpurine (zeatin riboside), 6-(3-methyl-2-butenyl) aminopurine (isopentenyladenosine, 2iPA) and N-(3-methyl-2-butenyl) adenine (isopentenyladenine, 2iP). The total cytokinin levels were low at leaf flush, with the zeatin and zeatin riboside in the buds about 70% of the total. In the transition of the terminal bud from leaf flush to dormancy, the principal cytokinins were zeatin-O-glucoside and zeatin riboside-O-glucoside. However, significant decreases in the levels of zeatin-O-glucoside and zeatin riboside-O-glucoside and increases in those of zeatin, zeatin riboside, 2iPA and 2iP were observed at flower bud initiation. It is suggested that in longan, the cytokinins that are translocated to the shoots are accumulated in the buds at the dormant stage, and that later there is a considerable increase in free cytokinins during flower bud initiation, leading to the promotion of flower bud development.
TL;DR: Relationships could not be observed between H and N explants grown under non-ventilated conditions probably due to the difficulty in discerning the plant status (N or H) and therefore, an underestimation of H microplants, supported by the low ability for acclimatization to ex vitro of N plants grown without ventilation.
Abstract: Endogenous indole-3-acetic acid (IAA), abscisic acid (ABA) and cytokinins (zeatin, zeatin riboside, dihydrozeatin, (diH)Z, dihydrozeatin riboside, (diH)[9R]Z, N6-isopentenyl adenine and N6-isopentenil adenine riboside) levels were evaluated in normal (N) and hyperhydric (H) microplants of Dianthus caryophyllus cultured under different aeration conditions in hormone-free liquid medium. The morphological differences between N and H explants grown under ventilated conditions were correlated with differences in their endogenous hormonal levels: after 15 and 30 days of culture, H explants showed lower IAA and ABA contents than N explants, as well as higher cytokinin levels, mainly of (diH)Z and (diH)[9R]Z. This was associated with less tissue differentiation and with an inability of H microplants to survive under ex vitro conditions. However, these relationships could not be observed between H and N explants grown under non-ventilated conditions probably due to the difficulty in discerning the plant status (N or H) and therefore, an underestimation of H microplants. This assumption is supported by the low ability for acclimatization to ex vitro of N plants grown without ventilation.
TL;DR: Endogenous levels of indole-3-acetic acid (IAA), cytokinins, gibberellins (GAs) and abscisic acid (ABA) in ‘Siji’ azalea, which had been sprayed once with 6-benzyl amino purine (6-BA) or decapitated, were determined by enzyme-linked immunosorbent assays.