Regeneration of <Emphasis Type="Italic">Aloe arborescens</Emphasis> via somatic organogenesis from young inflorescences

A system for in vitro regeneration of Aloe arborescens was developed using young inflorescences as explants. Different phytohormone combinations of N-phenyl-N′-1,2,3-thiadiazol-5-yl urea (TDZ), benzyladenine (BA), 6-(γ,γ-dimethylallyl-amino)purine riboside (2iPR), zeatin ribozide (ZR), N-(2-chloro-4-pyridyl)-N′-phenylurea (CPPU) and kinetin (K), with or without ancymidol, were examined in order to induce plant regeneration. Efficient shoot regeneration was initiated on Murashige and Skoog (MS) medium supplemented with BA or TDZ. MS medium enriched with 19.6, 22.2 μM BA and 3.92 μM ancymidol (MSBA5/1 medium), promoted organogenesis enabling 87.3% of the explants to regenerate 6.04 ± 1.79 shoots/explant. Subsequent shoot elongation and plant regeneration were strongly affected by the medium composition used for shoot induction. Optimal elongation (three to four shoots per explant) was obtained when shoots, initiated on MSBA5/1 medium, were subsequently transferred onto MS containing only 4.4 μM BA. Rooting was performed on MS media lacking growth regulators. Histological analysis revealed that the initiated shoots originated from the receptacle tissue surrounding the residual vascular tissue of the flower buds.     

Germplasm Preservation of Wild Arachis Species through Culture of Shoot Apices and Axillary Buds from In Vitro Plants

A study was conducted to evaluate in vitro techniques for germplasm preservation of wild species of Arachis. Nodal segments excised from in vitro-grown plants of A. retusa, A. macedoi and A. burchellii were used to examine the effects of explant position and age of the donor plant. Explants were excised from plants maintained in culture for 30, 60, 90 or 180 d, numbered I – V from top to bottom and cultured on MS medium supplemented with 2.7 µM NAA or different BAP concentrations (0, 4.4, 13.2 and 22 µM). The age of the donor plant has not influenced the responses of the four genotypes studied. In contrast, shoot regeneration ability was significantly affected by the original explant position, decreasing from top to bottom. In media supplemented with different BAP concentrations, multishoot formation was induced from apical segments at low frequencies (10 – 20%) and segments of all positions originated calluses at the explant basis after 30 d of culture. The culture of nodal segments in the presence of 2.7 µM NAA as the sole growth regulator is recommended for the multiplication of in vitro collections of wild groundnut species in order to avoid callusing and adventitious shoot formation.     

Effect of Combined Changes in Culture Medium and Incubation Conditions on the Regeneration from Immature Embryos of Elite Varieties of Winter Wheat

In this study, tissue culture method for plant regeneration from immature embryos of elite Hungarian winter wheat varieties was established. The influence of the growth regulators and the concentration of macroelements in the regeneration medium and of the incubation temperature and light intensity on regeneration frequency were investigated. The most noticeable effect on regeneration frequency was achieved by simultaneously reducing both the incubation temperature to 23 °C and the concentration of macroelements in the regeneration medium to half-strength. This modification increased the average regeneration frequency from about 10–78%. Changes in the light intensity and temperature gave an average plant regeneration frequency of 83%.     

Factors Affecting Plant Regeneration from Tissue Cultures of Chinese Leymus (Leymus chinensis)

Chinese leymus (Leymus chinensis Trin.) is a perennial grass of the Gramineae, which is widely distributed in China, Mongolia and in Russian-Siberian. In order to explore the potential of biotechnology for genetic improvement of this forage grass, an efficient tissue culture system was established and the factors affecting plant regeneration were evaluated. Immature inflorescence segments 3–5 mm in length from eight accessions were cultured on N6 medium supplemented with 2.26–22.60 µM 2,4-D. The callus induction frequency ranged from 72.11 to 82.19%. Shoots were differentiated from the calli on N6 medium containing 4.65 µM kinetin and 4.44 µM BA. Viable regenerants were developed on hormone-free medium. Normal plants were obtained after natural vernalization in the field. The plant regeneration frequency in Chinese leymus was associated with different genotypes and different combinations of growth regulators in medium. The concentration of 2,4-D in the callus induction medium had a strong effect on successive plant regeneration. Relatively higher concentrations of 2,4-D (i.e., 9.04 and 22.60 µM) were more favorable to the plant regeneration than lower ones (i.e., 2.26 and 4.52 µM). This is the first report on plant regeneration in vitro in L. chinensis.     

An improved and reliable chili pepper (Capsicum annuum L.) plant regeneration method

In this work we report a new method forin vitro chili pepper (Capsicum annuum L.) plant regeneration based on shoot formation from wounded hypocotyls. Chili pepper seeds were surface sterilized and germinated on agar (0.8%) at 25 ± 2°C in the dark. Five factors that may influence shoot regeneration were studied: age of seedlings, hypocotyl wounding site, time elapsed between wounding the hypocotyls and decapitation of seedlings, culture media and cultivars. In order to study the influence of the first three factors on shoot regeneration, the apical, middle or basal hypocotyl regions of seedlings of cv. Mulato Bajio at different stages of development (9, 15, 16, 21 and 28 d old) were wounded with a syringe needle, and the seedlings were cultured on MS semisolid medium without growth regulators at 25 ± 2°C under a 16/8 h light/dark photoperiod (daylight fluorescent lamps; 35 mol m-² s-^-1) until decapitation. The seedlings were decapitated (3 mm below the cotyledons) at different times after wounding (0, 2, 4, 10, 12 and 14 d), and each explant was evaluated for bud and shoot formation ( 5 mm in length) at the wounded site after 30 d of incubation. In general, seedlings at the stage of curved hypocotyl (9 d old) wounded in the apical region of hypocotyl were the best explants for shoot regeneration when inoculated on culture medium without growth regulators. Decapitation after wounding also influenced the shoot regeneration efficiency, with 10–14 d being the best period. Up to 90% shoot regeneration in cv. Mulato Bajio was obtained under these conditions. Statistically significant differences were observed for shoot formation among 21 cultivars tested. Regeneration of whole plants was achieved by rooting the shoots with indole-3-butyric acid pulses of 60 mg L^–1 for 3 h and then subculturing on MS medium without growth regulators.     

Factors affecting Agrobacterium-mediated transformation and regeneration of sweet orange and citrange

Epicotyl explants of sweet orange and citrange were infected with Agrobacterium strain EHA101 harboring binary vector pGA482GG, and factors affecting the plant regeneration and transformation efficiency were evaluated. Increasing the wounded area of explants by cutting longitudinally into two halves, and optimization of inoculation density, dramatically enhanced both regeneration and transformation frequency. Inclusion of 2,4-dichlorophenoxyacetic acid (2,4-D) in the explant pretreatment medium and the co-culture medium improved the transformation efficiency by decreasing the escape frequency. More than 90% rooting frequency of transformed citrange shoots was achieved by two-step culture: first on media supplemented with auxins, and then on media without hormones. Inclusion of 20 mg l^–1 kanamycin in rooting medium efficiently discriminated transformed shoots from non-transgenic escaped shoots. Shoot grafting in vitro was used to regenerate transformed plants, due to the slow growth of most sweet orange shoots.     

Factors affecting in vitro microrhizome production in turmeric

In vitro microrhizome production was obtained in turmeric (Curcuma longa Linn.). Freshly sprouted buds with small rhizome portions excised from stored mature rhizomes were cultured on semi-solid culture initiation medium –- MS basal medium + 0.88 M BAP (6-benzylaminopurine) + 0.92 M kinetin + 5% coconut water + 2% sucrose + 0.5% agar –- resulting in bud elongation. Multiple shoots were produced from these elongated buds by culturing in liquid shoot multiplication medium –- MS basal medium + 2.2 M BAP + 0.92 M kinetin + 5% coconut water + 2% sucrose –- at 25±1°C and 16-h light (at 11.7 mol m^–2 s^–1)/8-h dark cycles. Clumps of four to five multiple shoots/single shoots were used in various experiments. Cultures were incubated in the dark at 25±1°C. Half strength MS basal medium supplemented with 80 g l^–1 sucrose was found to be optimal for microrhizome production. Cytokinin BAP had an inhibitory effect on microrhizome production. At the highest concentration of BAP tried (35.2 M) microrhizome production was totally inhibited. Microrhizome production depended on the size of the multiple shoots used. Microrhizomes produced were of a wide range in size (0.1–2.0 g) and, readily regenerated when isolated and cultured in vitro on culture initiation medium or shoot multiplication medium. Under in vivo conditions, small (0.1–0.4 g), medium (0.41–0.8 g) and big (>0.81 g) microrhizomes regenerated. Plantlets developed from big microrhizomes grew faster.     

Age and Physiological Condition of Donor Plants Affect in vitro Morphogenesis in Leaf Explants of Passiflora edulis f. flavicarpa

The regeneration potential of D.alata L. germplasm preserved in vitro was compared with the micropropagation of fresh material. Nodal cuttings were conserved for 9 months in different treatments based on D-571 culture medium modified, using several variable components (mannitol, benzylaminopurine and activated charcoal). Regeneration at 8 weeks, assessed by means of percentage of explant regenerating and the multiplication at 5 weeks through the shoot length and de novo bud count formation per explant were determined. The results showed high rates (100 and 98%) of explant regeneration and micropropagation from in vitro material maintained in D-571 medium with 1.5% of mannitol + 0.1 or 1 mg l^–1 of benzylaminopurine + 2 g l^–1 of activated charcoal, respectively.     

Cryopreservation of in vitro-cultured multiple bud clusters of asparagus (Asparagus officinalis L. cv Hiroshimagreen (2n=30) by the techniques of vitrification

Summary A culture line of asparagus forming green bulbous structures consisting of numerous multiple bud clusters designated bud clusters was induced from a meristem culture of asparagus (Asparagus officinalis L.cv. Hiroshimagreen, 2n=30). Small cubic segments (2 mm3) cut from bud clusters were cryopreserved using three different cryogenic protocols. Only vitrification produced very high levels of shoot formation after cooling to –196°C. Segments were treated with a vitrification solution (PVS2) at 25°C for 45 min or at 0°C for 120 min prior to a direct plunge into liquid nitrogen. After rapid warming, the segments were expelled into Murashige and Skoog medium containing 1.2 M sucrose for 10 min and then plated on agar shoot outgrowth medium. The average rate of shoot formation of vitrified segments producing normal shoots was near 90% without any preculture and/or cold-acclimation treatment. Revived segments resumed growth within 3 days and developed about three shoots per segment. In vitro-cultured bud clusters appear promising as material for cryopreserving asparagus germplasm.Abbreviations DMSO dimethyl sulfoxide - PVS 2-vitrification solution - LN liquid nitrogen - IBA 3-indolbutyric acid - BA 6-benzylaminopurine - FDA fluorescein diacetate - DSC differential scanning calorimeter     

In vitro propagation of an endangered medicinal plant Saussurea involucrata Kar. et Kir.

An efficient micropropagation system for Saussurea involucrata Kar. et Kir., an endangered Chinese medicinal plant, has been developed. Shoot organogenesis occurred from S. involucrata leaf explants inoculated on medium with appropriate supplements of plant growth regulators. 66.0% of shoot regeneration frequency and 5.2 shoots per leaf explant were achieved when cultured on a medium containing 10 μM 6-benzylaminopurine (BAP) and 2.5 μM 1-naphthaleneacetic acid (NAA). Shoot organogenesis was improved further when the leaf explants were pre-incubated at low temperature, and 80.6% of shoot regeneration frequency was recorded with 9.3 shoots per leaf explant at 4°C by 5-day pretreatment period. Up to 87.0% of the regenerated shoots formed complete plantlets on a medium containing 2.5 μM indole-3-acetic acid (IAA) within 28 days, and 85.2% of the regenerated plantlets survived and grew vigorously in greenhouse condition. The phytochemical profile of the micropropagated plants was similar to that of wild plants. The regeneration protocol developed in this study provides a basis for germplasm conservation and for further investigation of medicinally active constituents of the elite medicinal plant.     

Plant regeneration from protoplasts isolated from embryogenic suspension cultured cells of Cinnamomum camphora L.

An efficient and reproducible protocol is described for the regeneration of Cinnamomum camphora protoplasts isolated from cultured embryogenic suspension cells. Maximum protoplast yield (13.1±2.1×10⁶/g FW) and viability (91.8±3.8%) were achieved using a mixture of 3% (w/v) cellulase Onozuka R10 and 3% (w/v) macerozyme Onozuka R10 in 12.7% (w/v) mannitol solution containing 0.12% (w/v) MES, 0.36% (w/v) CaCl₂·2H₂O, and 0.011% (w/v) NaH₂PO₄·2H₂O. First divisions occurred 7–10 days following culture initiation. The highest division frequency (24.6±2.9%) and plating efficiency (6.88±0.8%) were obtained in liquid medium (MS) supplemented with 30 g l^–1 sucrose, 0.7M glucose, 0.1 mg l^–1 NAA, 1.0 mg l^–1 BA, and 1.0 mg l^–1 GA₃. After somatic embryo induction and then shoot induction, the protoplast-derived embryos produced plantlets at an efficiency of 17.5%. Somatic embryos developed into well-rooted plants on MS medium supplemented with 1.0 mg l^–1 3-indole butyric acid (IBA). Regenerated plants that transferred to soil have normal morphology.     

An efficient protocol for plant regeneration from protoplasts of the moss <Emphasis Type="Italic">Atrichum undulatum P. Beauv in vitro</Emphasis>

A system for plant regeneration from protoplasts of the moss, Atrichum undulatum (Hedw.) P. Beauv. in vitro, is first reported. Viable protoplasts were isolated at about 9 × 10⁵ protoplasts g⁻¹ fresh weight from 10 to 18 days protonemata. For regeneration of protoplasts, viable protoplasts were cultured in liquid–solid medium containing surface liquid medium MS (0.4 M mannitol) and subnatant solid medium Benecke (0.3 M mannitol) at 20 °C under a 16-h photoperiod white light after 12 h preculture in darkness at 20 °C. The great majority of protoplasts follow a regenerative sequence: formation of asymmetric cells in 2–3 days; division of the asymmetric cells to 2–3 cells in 4–5 days, and further develop to produce a new chloronemal filament in 15 days. Juvenile gametophyte can be visible in 20 days. The plating ratio of cell cluster regenerated from protoplasts reaches up to 45%. Transient expression experiments indicate the electroporation uptake of DNA is possible.     

Plant regeneration from a cryopreserved embryogenic cell suspension of a commercial sugarcane hybrid (Saccharum sp.)

Efficient plant regeneration was obtained from a cryopreserved embryogenic cell suspension of sugarcane established from leaf derived callus. Pregrowing the cells for three days in MS basal medium supplemented with 0.33 M sorbitol was essential to the process. The cells were cooled at a rate of 0.5°C/min to –40°C and then stored in liquid nitrogen. Thawing was carried out rapidly in water at +40°C, and the cells were then plated without washing onto filter paper discs placed on a semi-solid regeneration medium (MS basal + 3% sucrose + 0.13 mg/1 2,4-D +0.25 mg/1 BAP + 0.25 mg/1 kinetin + 0.25 mg/1 zeatin). The filter paper discs, along with the cells, were transferred to the same, fresh medium after five hours. After 24 hours the cells were scraped off, placed on fresh semi-solid medium and incubated at 28°C in the dark for two weeks before transfer to light. A regeneration efficiency of 92% was obtained (regenerated plants, expressed as a percent of unfrozen control). Plants regenerated from cryopreserved cells, and grown to maturity in the greenhouse, were morphologically identical to regenerated control plants.Abbreviations DMSO dimethyl sulfoxide - PEG polyethylene glycol - 2,4-D 2,4-dichlorophenoxyacetic acid - BAP benzyl aminopurine - TTC 2,3,5-triphenyl tetrazolium chloride     

Efficient production of doubled haploid plants by immediate colchicine treatment of isolated microspores in winter Brassica napus

The effect of colchicine on embryogenesis induction and chromosomedoubling during microspore culture was evaluated in two F₁ hybridsofwinter oilseed rape (Brassica napus L.). Colchicinetreatment (50 and 500 mg/L) of isolated microspores during thefirst 15 h in culture stimulated embryogenesis and produced large amounts ofhealthy-looking embryos. These normal embryos germinated well at 24°C after being transferred to solid regeneration medium and aninitial period of low temperature (2 °C) for 10 days, andcoulddirectly and rapidly regenerate vigorous plants. A high doubling efficiency of84–88% was obtained from 500 mg/L colchicine treatment for15h with low frequency of polyploid and chimeric plants. Acolchicinetreatment duration of 6 h was less effective on embryogenesis anddoubling efficiency. The present experiment also showed that changing of induction medium 15h after microspore isolation produced higher spontaneous doublingefficiency, as compared with medium change 6 h after isolation.     

Direct plant regeneration from leaf explants of Plumbago species

Direct plant regeneration was achieved from leaf explants of Plumbago rosea and Plumbago zeylanica on Murashige and Skoog (MS) medium supplemented with 6.7 M 6-benzylaminopurine (BA), 1.4 M indole-3-acetic acid (IAA), 370 M adenine sulfate (Ads) and 3% (w/v) sucrose. The shoot initials developed within 2–3 weeks on the leaf margin as well as from the cut surface of the leaf. High frequency shoot-bud regeneration was achieved on similar medium in subsequent subcultures. The semi-mature leaves produced more shoot-buds as compared to the younger leaves. Mature leaves did not show any response for shoot bud initiation. More than 85% of the semi-mature explants produced shoot-buds per leaf explant within 4 weeks of culture. Shoots rooted on half-strength basal MS medium supplemented with 1.2 M indole-3-butyric acid (IBA) and 2% (w/v) sucrose; approximately 90% of the in vitro raised plantlets survived in the greenhouse. The regenerated plantlets looked morphologically similar to the mother plants. This protocol might be useful for genetic improvement programs.     

Liquid culture for efficient micropropagation of Wasabia Japonica (MIQ.) matsumura

Summary An efficient protocol for in vitro propagation of the valuable medicinal plant, Wasabia japonica (Miq.) Matsumura is described through shoot tip proliferation and direct regeneration. Multiple shoots were induced from shoort tips cultured on Murashige and Skoog (MS) semi-solid medium containing various concentrations (0.5–50 μM) of N⁶-benzyladenine (BA), thidiazuron, kinetin, and zeatin. A comparison was made on shoot multiplication between semi-solid and liquid culture media. Well-developed shoots were obtained using full-strength MS semi-solid medium containing 5.0 μM BA. However, the greatest shoot proliferation was achieved on either full- or half-strength MS liquid media supplemented with 5.0 μM BA for 4 wk (15.3±0.9 and 15.0±0.7 shoots per explant, respectively), and on half-strength MS liquid medium for 6 wk (25.8±1.3 shoots per explant) in culture. In contrast, the maximum number of shoots per explant on full-strength MS semi-solid medium was achieved with either 5.0 μM BA (10.4±0.6 shoots per explant) or 10.0 μM kinetin (10.9±0.8 shoots per explant). Fresh weight of explants and length of shoots derived from full-strength MS liquid medium (1055±77 mg and 34.2±1.0 mm, respectively) were significantly higher than those derived from full-strength MS semisolid medium (437.6±17.3 mg and 15.4±0.7 mm, respectively). Quarter-strength MS liquid medium had no significant difference in shoot proliferation when compared to quarter-strength MS semi-solid medium. Elongated shoots were separated and rooted on half-strength MS semi-solid media fortified with 1-naphthaleneacetic acid (NAA), indole-3-butyric acid (IBA), or indole-3-acetic acid (IAA) ranging from 0.1 to 10.0 μM. Root formation was greatest with IBA when compared with IAA and NAA. One hundred percent of shoots were rooted on half-strength MS medium with 5.0 μM IBA, while vigorous roots were obtained with 10.0 μM IBA. Micropropagated plantlets were successfully established in soil with 95% survival rate after heardening.     

Rapid plant regeneration and analysis of genetic fidelity of in vitro derived plants of Chlorophytum arundinaceum Baker—an endangered medicinal herb

An efficient in vitro multiplication system via multiple shoot bud induction and regeneration has been developed in Chlorophytum arundinaceum using shoot crown explants. Optimum regeneration frequency (87%) and desirable organogenetic response in the form of de novo organized multiple shoot buds without an intervening callus phase was obtained on Murashige and Skoog's (MS) minimal organics medium containing 3% sucrose (w/v) supplemented with 4×10⁻⁶ M Kn and 2×10⁻⁶ MIBA. Axenic secondary explants with multiple shoot buds on subculturing elicited best response with 1×10⁻⁵ M Kinetin (Kn) and 5×10⁻⁶ M indole-3-butyric acid (IBA) giving rise to an average of 18.74 shoots per culture with mean shoot length of 7.6 cm ± 1.73. Varying molar ratios of either Kn/IBA or Kn/NAA revealed statistically significant differences in the regeneration frequencies among the phytohormone treatments. It was observed that the shoot bud differentiation and regeneration was influenced by the molar ratios of cytokinins/auxin rather than their relative concentrations. Healthy regenerated shoots were rooted in half strength MS basal medium containing 3% sucrose (w/v) supplemented with 5×10⁻⁶ M IBA. Following simple hardening procedures, rooted plantlets, were transferred to soil-sand (1:1; v/v) with more than 90% success. Genetic fidelity was assessed using random amplified polymorphic DNA (RAPD), karyotype analysis and meiotic behaviour of in vitro and in vivo plants. Five arbitrary decamers displayed same banding profile within all the micropropagated plants and in vivo explant donor. The cytological and molecular analysis complemented and compared well and showed no genomic alterations in the plants regenerated through shoot bud differentiation. High multiplication frequency, molecular, cytological and phenotypic stability ensures the efficacy of the protocol developed for the production and conservation of this important endangered medicinal herb.     

Production of doubled haploid rice plants (Oryza sativa L.) by anther culture

The results of anther culture of F₂ pollen issued from 23 single crosses are presented. A relation between the morphology of the panicle and the microspore stage was established. After cold-pretreatment (8 days at 4°C), the anthers were cultured on the callus-induction medium N6 supplemented with 1 mg l^–1 naphthaleneacetic acid. The calli were transferred to MS plant regeneration medium supplemented with 3 mg l^–1 kinetin + 0.5 mg l^–1 naphthaleneacetic acid. The induction frequency varied from 0.22% to 29% and the regeneration frequency from 0% to 144.4%, dependent upon the crosses used. On average, 27% of the plants obtained were albinos and 59% of the green plants underwent spontaneous chromosome doubling. Thirtynine doubled haploid lines were evaluated and multiplied in the field. Lines with an excellent behaviour in upland culture conditions were selected from two crosses.     

In vitro propagation of Albizia odoratissima L.F. (Benth.) from cotyledonary node and leaf nodal explants

Summary Cotyledonary node and leaf nodal explants excised from 14-d-old in vitro-grown seedlings of Albizia odoratissima were cultured on a Murashige and Skoog (MS) medium with different concentrations of 6-benzylaminopurine (BAP), N ⁶-(2-isopentenyl) adenine (2-iP) and kinetin, used either solely or in combinations. The highest frequency for shoot regeneration (82.5%), the maximum number of shoots per explant (6.9), and the maximum shoot length (2.55 cm) were obtained from cotyledonary node explants cultured on a MS medium containing 10 &#x03BC;M BAP and 10 &#x03BC;M 2-iP with 30 gl^&#x2212;1 sucrose. Successful rooting was achieved by placing the microshoots on MS medium with 25 &#x03BC;M indole-3-butyric acid (IBA) for 24h first, then transferring to the same medium without IBA. Of the various substrates tested, vermiculite was best for plant acclimatization, in which 75% of plants survived.     

Adventitious shoot regeneration from leaf, stem and root explants of commercial cultivars of Gentiana

Several culture conditions were examined for promoting efficient plant regeneration from explants of Gentiana. Adventitious shoot regeneration from leaf explants of cv. WSP-3 was very superior on MS medium, compared to B5 medium, supplemented with four cytokinins (TDZ, 4PU-30, BA and zeatin). An auxin / cytokinin combination was required for regeneration. TDZ was the most effective cytokinin, while NAA was more effective than IAA or 2,4-D. Optimum conditions for regeneration from explants (leaf, stem and root) of cv. WSP-3, evaluated in terms of regeneration frequency and number of regenerated shoots per explant, were TDZ and NAA in combination, 5–10 mg/l and 0.1 mg/l for leaf and stem explants, and 10 mg/l and 1 mg/l for root explants, respectively. Application of these conditions to eight other commercial cultivars resulted in 30–100% regeneration from leaf explants. The number of chromosomes in each of ten regenerated plants of each cultivar was diploid, 2n=26. Shoots regenerated in vitro were rooted in phytohormone-free medium and transferred to soil.Abbreviations MS medium Murashige and Skoog's medium (Murashige and Skoog 1962) - B5 medium Gamborg B5 medium (Gamborg et al. 1968) - BA 6-benzylaminopurine - TDZ N-phenyl-N'-1,2,3-thiadiazol-5-yl urea - 4PU-30 N-(2-chloro-4-pyridyl)-N'-phenylurea - 2,4-D 2,4-dichlorophenoxyacetic acid - IAA indole-3-acetic acid - NAA 1-naphthaleneacetic acid