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Fang Geng, Renae Moran, Michael Day, William Halteman, and Donglin Zhang

sour cherry, 6 to 8 weeks was optimum for promoting shoot growth, but longer than 8 weeks was detrimental ( Borkowska, 1986 ). Cytokinin in the media is necessary for proliferation, but can inhibit shoot elongation at concentrations that promote rapid

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Servet Kefi, Paul E. Read, Alexander D. Pavlista, and Stephen D. Kachman

The role of sucrose alone and in combination with different cytokinin-like compounds on the microtuberization of potato, Solanum tuberosum `Atlantic', was investigated. Single nodal segments were placed in Magenta boxes containing Murashige & Skoog medium supplemented with one of 15 treatments in a 3 × 5 factorial. Treatment factors were sucrose at 3%, 6%, or 9%, and cytokinin-like compounds at five levels [cytokinin-free; 2 mg kinetin/L; 0.1 mg thidiazuron (TDZ)/L; 1.0 mg AC 243,654/L; 0.1 mg AC 239,604/L]. Except in a few cases in kinetin and TDZ treatments, nearly all cytokinin treatments failed to induce tuberization at the 3% sucrose, noninductive level. However, all cytokinin treatments induced tuberization in the presence of 6% sucrose. By raising the sucrose level from 6% to 9%, more and larger microtubers were obtained in the cytokinin-free medium. At the 9% sucrose level, even though more tubers per box were produced by TDZ and AC 243,654 treatments, less total fresh weight of tubers per box resulted from kinetin, TDZ and AC 243,654 treatments because tubers formed were smaller. Higher sucrose concentrations (9%) favored tuberization in the cytokinin-free medium, whereas 6% sucrose was optimum for the medium containing cytokinins. Sucrose might produce a strong tuberization signal that might either change endogenous hormone levels affecting tuberization or activate a number of genes coding tuber proteins and enzymes related to starch synthesis.

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David G. Clark, John W. Kelly, and H. Brent Pemberton

Six cultivars of potted rose (Rosa ×hybrida L.) plants were evaluated for shipping stress-induced leaf chlorosis during holding at 8, 16, or 28C for 2, 4, or 6 days. `Meijikatar' showed more leaf chlorosis than the similar `Meirutral' at the higher simulated shipping temperatures and longer durations. Plants of `Meijikatar' were treated before simulated shipping with BA, TZ, or Promalin at 0, 25, 50, or 100 mg cytokinin/liter each, then paper-sleeved and stored in the dark in fiberboard boxes at 16C for 5 days. Plant quality 5 days after removal from storage was better with BA at 50 or 100 than at 0 mg·liter–1. All cytokinin-treated plants showed less leaf chlorosis than controls. Benzyladenine at 50 or 100 mg·liter–1 reduced leaf chlorosis when compared to all TZ treatments. There were no differences among treatments in the number of etiolated shoots per plant. Chemical names used: N-(phenylmethyl)-1H-purin-6-amine (benzyladenine, BA); trans-zeatin (TZ); gibberellic acid (GA4+7) + BA (Promalin).

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Saila T. Karhu

Microshoots of `McIntosh' apple (Malus domestica Borkh.) were grown on Murashige-Skoog (MS) nutrient medium supplemented with either sucrose or sorbitol or with sucrose and an elevated level of cytokinin. Shoot growth was recorded and concentrations of fructose, glucose, sorbitol, and sucrose were analyzed in nutrient media and shoots during a 6-week subculture period. Axillary branching was stimulated by high cytokinin and sorbitol media, with increased biomass production and carbohydrate use on the high-BA medium only. The sucrose in the nutrient medium was hydrolyzed to fructose and glucose, which were equally taken up by shoots. Sorbitol was taken up somewhat less effectively. The elevated level of BA decreased sucrose hydrolysis in the nutrient medium. There were high concentrations of sorbitol in shoots grown on the sorbitol medium, and sorbitol also accumulated at the end of the culture period in shoots grown on sucrose. The amount of sucrose was low, and glucose was more abundant than fructose in microshoots. The starch content of leaves was not affected by treatments or sampling time. Chemical names used: N6-benzyladenine (BA).

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M.H. Aboul-Nasr, S.Z. Elagamy, and A.M. Kassim

Three strawberry cultivars were used in this study. Runners from the three cultivars were grown on Murashige and Skoog medium supplemented with benzylaminpurine or kinetin at four concentrations (2, 1, 0.5, and 0.25 mg·L-1 in addition to the control treatment). The use of cytokinin, regardless of type and concentration, promoted the explant proliferation, shoot height, number of leaves, and plantlet fresh weight. Callus formation was enhanced by BA application, especially with `Pajaro'. However, `Chandler' did not form at all using cytokinin. Produced plantlets had lower nutrient constituents (N, P, K, Ca, and Na) when grown on media containing cytokinin compared to the control. Based on these results, cytokinin is recommended to get more shoots per explant. Furthermore, using the lowest concentration (0.25 mg·L-1) will produce height proliferation, greater shoot length, and more leaves.

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Mark H. Brand, Yiqin Ruan, and Richard Kiyomoto

To characterize the in vitro behavior of Rhododendron `Montego' with tissue proliferation (TP) to cytokinin and auxin, comparisons were made of normal [TP(–)], dwarf TP [TP(+) dwarf], and long TP [TP(+) long] shoot cultures. On basal medium TP(–) and TP(+), long shoots failed to multiply and had a low relative growth rate (RGR) of 0.1, whereas TP(+) dwarf shoots produced 31.8 shoots per tip, with most shoots being <5 mm long, and RGR was 0.3. Addition of 15 μm 2iP to basal medium induced the production of more than six shoots per TP(–) tip and doubled their RGR; TP(+) long shoots produced 16.8 shoots, most <5 mm long, and had an RGR of 0.3; TP(+) dwarf shoots produced only 16% as many shoots as on basal medium, but still exhibited an increase in RGR. Leaves from TP(–) and TP(+) sources failed to produce shoots on basal medium, but 74% of TP(–) leaves formed shoots when cultured on 1 μm IBA and 30 μm 2iP. TP(+) leaves were able to form shoot meristems on media containing only 5 μm 2iP (26% of explants), but these meristems failed to elongate into shoots. Calli from TP(–) leaves, TP(+) leaves, and TP(+) tumors grown on medium containing 10 μm NAA and 15 μm 2iP had higher RGRs than the same calli on basal medium during the first 8 weeks of culture. Over time, RGR decreased in both TP(–) and TP(+) leaf calli, but increased in TP(+) tumor callus. The increased RGR resulted from differentiation of shoot meristems on 85% of the calli between week 4 and week 8. Our results suggest that TP(+) tissues have altered hormone metabolism or sensitivity that leads to dramatic differences in in vitro behavior and probably contributes to tissue proliferation observed in whole plants. Chemical names used: 6-(γ,γ-dimethylallylamino) purine (2iP); indole-3-butyric acid (IBA); α-naphthaleneacetic acid (NAA).

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Yong-Ping Gao, Hino Motosugi, and Akira Sugiura

Ungrafted trees of seven apple rootstock cultivars, M.4, M.7, M.11, M.26, M.27, MM.106, and Maru. bakaidou (Malus prunifolia Borkh. var. ringo Asami; weeping type), and `Fuji' (Malus domestics Borkh.) trees grafted on these seven plus M.9 and M. 16 rootstock were grown in sand. They were regularly supplied with nutrient solutions of N as ammonium alone (A), nitrate alone (T), and both (AT). With both ungrafted and grafted trees, the shoot growth of six rootstock (M.11, M.4, M.7, MM.106, M.26, and M.27) was significantly less with A than with T. With `Fuji' trees grafted on the above six rootstock, the number of flowering buds and the ratios of flowering buds to total emerged buds were significantly enhanced by treatments A and AT, especially in the formation of axillary flowering buds. Flowering and shoot growth of `Fuji' trees grafted on M. prunifolia and M.16 were slightly affected by the form of supplied N. In the xylem sap, cytokinin-like activity was detected in a single zone in paper chromatography in all rootstock and `Fuji' trees. The activity in six ungrafted rootstock (M.4, M.7, M.11, M.26, M.27, and MM.106) and `Fuji' trees grafted on these plus M.9 rootstock were higher with A than with T. Gibberellin-like activity in the same sap was detected in two zones, Rfs 0.3 to 0.4 and Rfs 0.7 to 0.8 in paper chromatography. In the six ungrafted rootstock and in `Fuji' trees grafted on these plus M.9, A led to higher activity at Rfs 0.7 to 0.S, but T led to higher activity at Rfs 0.3 to 0.4. Cytokinin-like and gibberellin-like activities in ungrafted M. prunfolia and `Fuji' trees grafted on M. prunifolia or M.16 were not affected by the form of N.

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Ann C. Smigocki and Iris J. Honeczy

Lycopersicon esculentum cv. UC82b cotyledons were co-cultivated with A. tumefaciens carrying vectors with modified isopentenyl transferase (ipt) genes. The ipt gene was placed under the control of the RUBISCO promoter in both the sense and antisense orientation. Over 50 transformants were recovered on kanamycin-containing media. Seeds from RO plants were germinated on selective media and R1 plants transformed with the ipt gene identified by PCR and Southern blot hybridization. Phenotypes of the R1 plants, whether transformed with the ipt gene in the sense or antisense orientation, were comparable to the control plants transformed with an inactive cytokinin gene. Fruit weights from both were similar to those from control plants, however, yields were reduced and ripening delayed. Most fruit had no seeds or very few small seeds. Cytokinin levels are being determined in order to correlate them to the observed phenotypes.

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F. A. Hammerschlag and A. C. Smigocki

Transgenic plants containing introduced phytohorm one genes have been shown to display altered growth and morphogenetic potential. Peach plants transformed with the ipt gene from Agrobacterium tumefaciens strain tms 328::T n5 and containing elevated levels of cytokinins were screened in vitro for compact growth habit on four different levels of 6-benzyladenine (BA). After nine weeks in vitro, the average number of axillary shoots per plant foe two of the transformants, 99-1 and 40-1, ranged from 1.5 to 6.6 times that for the controls on 0-30 uM of BA, whereas average fresh weight ranged from 1.1 to 3.6 times that for the controls. One of the transformants, 94-1, produced a greater number of axillary shoots only on 30 μM BA. Rooted plants derived through micropropagation from the original transformants were monitored for 30 months under greenhouse conditions. The average height of transformants 94-1 and 99-1 after six months in the greenhouee was 88 and 77% of controls, respectively and after 30 months was 90 and 75% of controls, respectively. In comparison to controls, transformants exhibited a greater number of branches per meter per plant after six weeks, but a lesser number after 30 months. These results suggest that the introduction of a cytokinin gene may be a useful approach to obtaining peach trees with a compact growth habit.

Open access

Rongpei Yu, Ying Cheng, Yanfei Pu, Fan Li, and Shugang Lu

-sterilized frond tips were inoculated on 1/2 MS media ( Murashige and Skoog, 1962 ) that contained cytokinin, 3% (w/v) sucrose, and 0.7% (w/v) plant agar and adjusted to pH 5.8 before being autoclaved. Using plant growth regulator (PGR)-free 1/2 MS medium as a