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Yung-I Lee

m above sea level) and were used as plant materials. The axillary buds of terminal shoot buds of rhizomes were used as the explant sources ( Fig. 1A ). Shoot buds were first washed with detergent and rinsed under running tap water for 1 min and then

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Yeun Joo Huh, Seoung Youl Choi, Hak Ki Shin, and Chun Ho Pak

Nonbranching chrysanthemums [Dendranthema × grandiflorum (Ramat.) Kitamura] are preferred because they require less labor in disbudding. High temperature is responsible for this phenotype of not having axillary buds or poor lateral shoot development. This study attempted to find out the effect of temperature and identify the involvement of endogenous polyamine contents in axillary bud formation of nonbranching chrysanthemum cv. Iwanohakusen. Plants were treated at 22, 26, 30, 34, and 38 °C for 9 hours midday for 2 months. Polyamine content [putrescine (Put), spermidine (Spd), spermine (Spm)] was analyzed 1 month after treatment and axillary buds were counted when the flowers opened. Results revealed that viable axillary buds decreased remarkably at 30 and 34°C. It was also found out that not only low temperature, but also the excessively high temperature of 38 °C induced axillary bud formation. Exposure to 38 °C increased the Put contents and resulted in high Put/(Spd + Spm) ratio as 22 °C, 26 °C. Temperature of 30, 34 °C lowered Put/(Spd + Spm) ratio. Results further showed that not polyamine contents, but polyamine ratio (Put/Spd + Spm) or transformation of Put to Spd and Spm may be involved in the axillary bud formation in nonbranching chrysanthemum.

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Unaroj Boonprakob, David H. Byrne, and Dale M.J. Mueller

Actively growing shoots of peach [Prunus persica (L.) Batsch] were collected every 2 weeks throughout the 1989 growing season. The samples were sectioned longitudinally and transversely to observe axillary bud initiation, which occurred in all samples collected. Differentiation of axillary bud meristems from early season samples (mostly normal nodes) included apical and prophyll formation, with procambium connected to the stem procambium. Little to no differentiation of such structures occurred in the late-season samples (mostly blind nodes). Other results suggest that blind node formation is a consequence of a lack of bud differentiation rather than a failure of bud initiation.

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Azza Tawfik, P. E. Read, and S. S. Salac

A method is described for obtaining explants free of bacterial contamination and for clonal propagation by in vitro culture of liatris axillary buds. Axillary bud growth was stimulated by removal of the shoot tips of greenhouse grown stock plants. Prior to using this approach, extreme bacterial contamination occured when explants were taken from stock plants that had not been decapitated. However, these axillary buds (0.3-0.5 cm long) were successfully established free of bacterial contamination when excised, surface disinfested and cultured on Murashige & Skoog (MS) medium supplemented with various levels of benzyladenine (BA) or kinetin and gibberellic acid (GA3). The highest number of leaves and greatest shoot length were produced by buds cultured on a medium supplemented with 1.0 mg/l BA plus 1.5 mg/l GA3. Shoot number was increased on medium containing 1.0 or 2.0 mg/l BA plus 0.5 mg/l GA3. Kinetin significantly increased the leaf number of the buds but there was no effect of kinetin on the shoot length or number. Shoots formed roots in a medium supplemented with 3 mg/l indole-3-butyric acid (IBA) plus 9 mg/l GA3. The plantlets were transferred to vermiculite and acclimatized successfully under intermittent mist in a greenhouse.

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S. Guzman, H. Alejandro, J. Farias, A. Michel, and G. Lopez

Watermelon (Citrullus vulgaris Schrad.) is a widely grown crop throughout the tropics and subtropics. In Mexico, it is an economically important crop. In vitro adventitious shoot regeneration of watermelon has been reported from shoot tip culture, leaf, hypocotyl, and cotyledons. Hence, the objective of this study was to evaluate in vitro plant regeneration from axillary buds of triploid watermelon. Axillary buds explants were prepared from shoot of commercial cultivar in field of 60 old day plants. Explants of 2 to 3 mm were incubated 2 weeks on Murashige and Skoog (MS) shoot regeneration medium containing 2.5 mg/L kinetin (KT) or indole-3-butyric acid (IBA), or gibberellic acid (GA3), followed by 3 weeks on shoot elongation medium supplemented with different combinations of the same phytohormones. The percentage of explants (83% to 90%) that produced shoots, expansion in size of explant (0.81–1 cm) and shoot length (6 mm) were highest in MS medium containing KT or IBA. In the shoot elongation step, shoot length (0.9–1 cm) and leaves number (6–7) were highest in MS medium supplemented with 2.5 mg/L of KT or GA3 and 0.2 mg/L IBA, but the better induction of roots in elongated shoot occurred on MS medium with 2.5 mg/L KT and 0.2 mg/L IBA. The results show that axillary buds from watermelon is an alternative for the micropropagation of this crop.

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Maritza I. Tapia, P.E. Read, H.F. Kaeppler, and P.L. Herman

Direct DNA delivery via microprojectile bombardment has been successfully used to transform a wide range of species. Transformation using this system is dependent on the optimization of several parameters. These parameters involve the explant, the gene construct, and parameters in the bombardment system. DNA was delivered into bisected axillary buds of grape hybrids `Chancellor' and `Valiant'. Target tissues were bombarded with gold microprojectiles coated with GUS::NPTII fusion gene construct(pBI426). Several experiments with varying parameters were conducted in order to increase the frequency of DNA delivery. Data were analyzed as a completely random design with 6 single petri dish as a replication and 50-60 bisected axillary buds per replication in each treatment. The treatment design was the single-factor method. Higher frequencies of transient transformation were obtained using microprojectiles of 1.6 μm diameter, adding 0.15 m mannitol and 0.15 m sorbitol, under a pressure of 68.6 cm Hg and a target distance of 6 cm. After 40 days on the selection medium containing 50 mg kanamycin/L regenerated plantlets were obtained and 40% of them expressed the GUS gene. The biolistic approach using bisected axillary buds as target tissue could be a method to achieve stable transformation and transgenic grape plants.

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Sudarsono and Ronald G. Goldy

Four muscadine grape (Vitis rotundifolia Michx.) cultivars (Carlos, Noble, Regale, and Tarheel) were evaluated for their ability to be cultured in vitro. Axillary buds were placed on Murashige and Skoog medium as modified by Chee. Different levels of benzylaminopurine [(BA) 0.5 to 10.0 μm], kinetin [(KIN) 0.5 to 5.0 μm], and thidiazuron [(TDZ) 0.5 to 11.3 μm], and different explant positions were evaluated for their effect on in vitro explant establishment and shoot production. Thidiazuron (2.3 to 4.5 μm) alone or in combination with BA (1.0 to 5.0 μm) or KIN (1.0 or 5.0 μm) was effective for establishing axillary buds. Similar levels were also effective for promoting shoot proliferation. Explants originating from the 10 basal nodes of a shoot with at least 25 nodes gave better shoot proliferation than explants originating from the 10 distal nodes. Chemical names used: 6-benzylaminopurine, 6-furfurylaminopu. rine (kinetin):N -phenyl-N'-l,2,3 -thiadiazol-5-y lurea (thidiazuron).

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James E. Faust and Royal D. Heins

Poor lateral branching sometimes occurs when certain poinsettia (Euphorbia pulcherrima) cultivars are pinched. Two experiments were conducted to determine the effect of high temperatures on axillary bud development. In Expt. 1, `Red Sails' plants were grown in a high-temperature environment (HTE) of 27°C at night (8 hr) and 30°C (3 hr), 33°C (10 hr), and 30°C (3 hr) in the day for two months, then transferred to a 20°C environment. In Expt. 2, plants grown at 20°C were transferred into the same HTE described above for 0, 2, 4, 8, 16, or 32 days and were then moved back into the 20°C environment. Axillary buds were examined for viability at the end of each experiment. In Expt. 1, only 8% of the lateral buds forming in the HTE were viable, while 80% of the buds forming in leaf axils of leaves unfolding after the plants were transferred to the 20°C environment were viable. In Expt. 2, 80% of buds produced in axils of the first four leaves to unfold after the start of the experiment were viable in all the treatments. However, the percentage of viable buds in the axils of leaf numbers 5 to 8 was 100, 100, 100, 96, 56, and 0 for the plants placed in the HTE for 0, 2, 4, 8, 16, and 32 days, respectively. These data indicate day temperatures of 30 to 33°C adversely affect lateral shoot development of `Red Sails' poinsettia.

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James E. Faust and Royal D. Heins

The effect of temperature on axillary bud and lateral shoot development of poinsettia (Euphorbia pulcherrima Willd.) `Eckespoint Lilo' and `Eckespoint Red Sails' was examined. Rooted `Eckespoint Lilo' cuttings were transplanted and placed into growth chambers maintained at 21, 24, 27, or 30 °C for 2 weeks before apex removal. The percentage of nodes developing lateral shoots after apex removal was 68%, 69%, 73%, or 76% at 21, 24, 27, or 30 °C, respectively. Cuttings were removed from the lateral shoots, rooted, and placed into a 21 °C greenhouse, and the apices were removed. The percentage of nodes developing into lateral shoots on cuttings taken from plants held at 21, 24, 27, and 30 °C were 74%, 65%, 66%, and 21%, respectively. Of the cuttings in the 30 °C treatment, 83% of the nodes not producing a lateral shoot had poorly developed axillary buds or no visible axillary bud development. Visual rating of axillary bud viability decreased from 100% to 0% when `Eckespoint Red Sails' plants were transferred from a 21 °C greenhouse to a greenhouse maintained at 27 °C night temperature and 30 °C for 3 hours followed by 33 °C for 10 hours and 30 °C for 3 hours during the 16-hour day. Transfer from the high-temperature greenhouse to a 21 °C greenhouse increased axillary bud viability from 0% to 95%. Axillary buds of leaves not yet unfolded were sensitive to high temperatures, whereas those of unfolded leaves (i.e., fully developed correlatively inhibited buds) were not. Sixteen consecutive days in the high-temperature treatment were required for axillary bud development of `Eckespoint Red Sails' to be inhibited.

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Mark A. Ritenour, Ellen G. Sutter, David M. Williams, and Mikal E. Saltveit

This study was undertaken to determine if endogenous IAA content and axillary bud development correlate with phenylalanine ammonia-lyase (PAL) induction and russet spotting (RS) susceptibility among RS susceptible and resistant cultivars of Iceberg lettuce (Lactuca sativa L.). Final levels of ethylene-induced PAL activity and RS development were highly correlated among cultivars, field conditions, and harvest dates. Harvested Iceberg lettuce midribs contained relatively low amounts of free IAA (maximum of 5.2 ng·g-1 fresh weight). There was poor correlation between free IAA content in lettuce leaf midribs and final RS development among all cultivars, growing conditions, and harvest dates. Axillary bud development, as measured by the number of visible buds per head, bud weight, or bud length, were not significantly correlated with final RS development or midrib IAA content. Cultivars with higher initial free IAA content lost much of their IAA after 8 days storage at 5C in air ± ethylene.