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Jacques J. Crabbe

The flushing behavior of shoot growth and its consequences on shoot differentiation are important features in fruit tree development, with regard to flowering ability. In this respect, two different approaches were applied to young `M26' apple trees. First, poorly branched 2-year-old trees were headed back, either in the second-year or in the first-year wood, at different times from right before to 6 weeks after budbreak. Early pruning resulted in rapid and prolonged regrowth, with a final very similar shaping of the tree to that of the intact controls. Late pruning, in contrast, leads to a two-step reaction (late spring and summer flushes), sometimes stronger on 2-year-old than on 1-year-old wood. In a second experiment, buds and young shoots were sampled on pruned trees in locations where they could be supposed to remain short shoots or grow long, with one or two flushes. They were weighed, their leaves and internodes measured, and the plastochron evaluated. During budbreak and the first month afterwards, shoot differentiation appears achieved. The primary difference between long and short shoot types does not consist in faster internode elongation but, rather, in faster production (reduced plastochron) of larger leaves.

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Qudsia Hussaini, Chiwon W. Lee, and Shanqiang Ke

Leaf sections of Echinacea purpurea obtained from greenhouse-grown plants were cultured on Murashige and Skoog (MS) medium supplemented with 0.5 to 4.0 μM benzyladenine (BA) and 0.1 to 10.0 μM naphthaleneacetic acid (NAA). The efficiency of adventitious shoot formation from leaf explants varied depending on growth regulator concentrations. About 90% of leaf tissues cultured with 20 μM BA and 0.1 μM NAA produced shoot differentiation. Initially, the adventitious shoot buds were purplish-red in color; they turned to green shoots as young leaves began to unfold. The individual shoots, when excised and subcultured on the MS basal medium containing 10 μM gibberellic acid (GA3), produced 15 to 20 new shoots per culture within 4 weeks.

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Jodie L. Ramsay, Donald S. Galitz, and Chiwon W. Lee

Influences of culture media and sucrose concentrations on plant regeneration from Easter lily (Lilium longiflorum L. cv. Ace) ovary tissues were investigated. Pistils excised from unopened flower buds (3-5 cm long) were sectioned and cultured on either B-5 medium or Murashige and Skoog (MS) medium containing 2%, 5%, or 10% sucrose, with 1 mg·L-1 2,4-D and 2 mg·L-1 BA. Callus formation was most prolific on MS medium containing 5% sucrose. Shoot differentiation was higher on MS medium than on B-5 medium. Rooted plants were transferred into soil medium and grown in a greenhouse. Root tip smears showed that 35% of the regenerated plants showed a variation in chromosome numbers from 10 to 25 per cell, while the rest of the regenerants showed the normal 2n = 2x = 24 chromosomes per cell. The mixoploid condition also existed in different root cells of the same regenerated plant. Chemical names used: 2,4-dichlorophenoxyacetic acid (2,4-D); 6-benzylaminopurine (BA).

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Chiwon W. Lee, Joel T. Nichols, Lijuan Wang, and Shanqiang Ke

Excised leaf sections of lance coreopsis cultured on Murashige Skoog (MS) medium produced adventitious shoots in response to BA. When the combinations of 0, 0.5, 1, or 2 μm NAA with 0, 5, 10, 20, or 40 μm BA were tested, shoots were induced by any of the four BA concentrations used in the medium, regardless of the presence of NAA. The average number of shoots formed per leaf section ranged from 1.4 to 4.3 seven weeks after culture initiation. Roots were induced at the base of individual shoots on the same regeneration medium when cultures were kept longer than 7 weeks. The rooted plants were transferred successfully into soil. The regenerated plants had the same growth and flowering characteristics as the seed-grown plants. Chemical names used: benzyladenine (BA); naphthaleneacetic acid (NAA).

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Boling Liu, Hongzhou Fang, Chaorong Meng, Ming Chen, Qingdong Chai, Kai Zhang, and Shijuan Liu

-naphthaleneacetic acid on the growth rate of callus of H. turgida . Data recorded after 30 d. Adventitious shoot differentiation. Each callus was cut into small pieces of around 2 cm 2 and transferred to the MS medium containing 0, 1.0, 2.0, or 3.0 mg·L −1 BA in

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Jodie L. Ramsay, Donald S. Galitz, and Chiwon W. Lee

Influences of culture media, sucrose, and growth regulator concentrations on plant regeneration from Easter lily (Lilium longiflorum L.) were investigated. Ovary tissues excised from unopened flower buds (3-10 cm long) were cultured on either B-5 medium or MS medium containing 2, 5, or 10% sucrose, 0.8% agar or Phytagel, and varying concentrations of 2,4-D, kinetin, naphthaleneacetic acid (NAA) and benzyladenine (BA). Callus formation from explants was more prolific on MS medium than on B-5 medium and when cultures were initially placed in the dark for 20 days. Cultures grew best when the medium contained 5% sucrose. Shoot differentiation from callus was maximum when MS medium contained 1 mg/liter 2,4-D and 2 mg/liter BA. Roots developed when shoots were placed on the same medium with 1 mg/liter 2,4-D, 0.1 mg/liter NAA and 0.1 mg/liter kinetin. Rooted plants were successfully transferred into soil medium in a greenhouse.

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Rajendra Maurya*, Nathu Ram Godara*, and Ram C. Yadav*

Influence of culture media and hormone concentrations on plant regeneration from rose (Rosa hybrida L. cv. Raktagandha) leaf segments were investigated. Leaves were excised from healthy, well-grown and mature plants. Leaf segments (4-5 mm long) were sectioned and cultured on Murashige and Skoog (1962) medium containing different concentration of growth hormones. Callus formation was most prolific (97.09%) on MS medium containing MS basal salts + 0.5 mg·L-1 BAP + 2.0 mg·L-1 2,4-D. maximum (56.67%) organogenesis or shoot differentiation was achieved on MS modified medium supplemented with 1.0 mg L-1 BAP + 0.1 mg·L-1 NAA + 10.0 mg·L-1 Adenine Sulphate. The highest percentage (93.73%) of in-vitro rooting was observed in half-strength MS basal medium containing 0.5 mg·L-1 IBA. Rooted plants were transferred in to sterilized potting mixture and grown in a greenhouse.

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Jocelyne Kervella, Loïc Pagès, and Michel Génard

Leaf emergence was studied on main and first-order shoots of peach and nectarine [Prunus persica (L.) Batsch.] trees belonging to nine standard cultivars, during their first growing season. The number of emerged leaves was recorded on main shoots (originating from the grafted buds) and on first-order shoots (inserted directly on main shoots). Similarly shaped leaf emergence curves were observed on main and first-order shoots for all the cultivars. Leaf emergence rate decreased gradually as the number of leaves increased. The number of emerged leaves could be modeled as a monomolecular function of accumulated thermal units. Significant differences were found between cultivars in a multiple analysis of variance of the model parameters, for main and first-order shoots. The ranking of the cultivars was similar for both types of shoots. Leaf emergence rate was lower on first-order shoots than on main shoots. Differentiating between shoot types is necessary for a reliable comparison of genotypes.

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Chang-Yeon Yu and John Masiunas

Repeated callus sub-culture reduce the regeneration capacity in many species. Our studies determined the effect of genotype and medium on regeneration of several Solanum and Lycopersicon genotypes from long-term callus cultures. In the first study, 13 genotypes were transferred to regeneration medium, including: Murashige and Skoog plus Gamborg Vitamins (MG); Murashige and Skoog (MS); Gamborg (GM); and white (WM). The greatest shoot regeneration was on the MG medium, containing the highest levels of thiamine. Shoot differentiation was greatest with 0.2 mg/l IAA and 2 mg/l BA. No plants were regenerated on GM or WM medium. In a second study, the effect of thiamine (0 to 200 mg/l) on shoot regeneration of the L. peruvianum genotypes PI199380, PI126945, PI251301, and PI128652, along with Solanum ptycanthum, Solanum nigrum, and L. esculentum `Diego' was evaluated. Shoot regeneration of Solanum ptycanthum, Solanum nigrum, L. peruvianum PI 199380 and PI25301 was best with 20 mg/l of thiamine.

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L. Xu, G.F. Liu, and M.Z. Bao

produced at 1.14 μ m TDZ. Results were generally similar to those in L. styraciflua with 0.45–2.27 μ m TDZ ( Kim et al., 1997 ). In L. styraciflua , most buds and shoots differentiated without any intervening callus formation, and even at 22.7 and 45