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Jeff S. Kuehny, William B. Miller, and Dennis R. Decoteau

Rooted cuttings of Ligustrum japonicum Thunb., an episodically growing species, were grown hydroponically in a controlled-environment growth chamber to determine allocation of glucose, mannitol, total soluble sugars, and total protein in mature leaves, flush leaves, stems, and roots. During the 65 days of episodic growth, 43% of the total soluble sugars was glucose and 33% mannitol. Glucose concentrations of mature leaves decreased during the first root growth episode, increased in almost all plant tissue during a shoot growth episode and decreased in all plant tissue at initiation of a second root growth episode. Mannitol concentrations in the roots and stems decreased during episodes of root growth and increased during a shoot growth episode when leaf flush mannitol concentrations increased. Radiolabeled C applied to leaves before the initiation of the first period of shoot elongation was translocated to the roots. After shoot elongation, just before a root growth episode, most labeled C was translocated to new shoots and roots. Autoradiographs indicated that subsequent episodes of shoot growth were supported by photosynthate from the previous shoot flush. Protein concentrations decreased in all plant tissues during shoot growth but increased in roots and mature leaves during root growth. Concentrations of 15N in leaf and stem tissue indicated retranslocated N supported each episode of shoot growth. Changes in endogenous C and N concentrations and allocation patterns in ligustrum were linked to the control of episodic shoot and root growth.

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Y. Mohamed-Yasseen, T. L. Davenport, W. E. Splittstoesser, and R. M. Skirvin

Bulb formation in vitro is considered to be advantageous over shoot formation. Bulbs were farmed in vitro from onion inflorescence explants cultured in bulb induction medium composed of Murashige and Skoog (MS) medium supplemented with 120 g/l sucrose and 5 g/l activated charcoal under long day photoperiod. Bulbs were also induced in the same medium from shoots which were first regenerated from onion inflorescences in MS alone or MS containing either 4.4 uM benzyladenine or 0.005, 0.01, 0.05, 01 0.1 uM of thidiazurone. This system of in vitro bulb formation obviates shoot elongation, rooting, and acclimatization steps normally required when shoots are regenerated.

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Jyothi Prakash Bolar, John L. Norelli, Herb S. Aldwinckle, and Viola Hanke

To root tissue-cultured apple cultivars, shoots from proliferating cultures were first transferred to root induction medium with IBA for 1 week in the dark. Shoots were later transferred to the same medium without IBA and incubated under light for elongation of the roots. Rooted shoots were then transferred to Jiffy-7s supplemented with biological plant protectant and fertilizer, and incubated in plastic humidity trays. After 2 to 3 weeks, plants were transferred to pots and covered with plastic bags to facilitate acclimation. This technique has resulted in 70% to 100% of shoots selected in vitro producing vigorously growing, healthy plants in the greenhouse. Chemical name used: indolebutyric acid (IBA).

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I-lun Lu, David W. Burger, and Ellen G. Sutter

Long term exposure to high benzyladenine (BA) concentrations inhibited shoot elongation and root growth of Cymbidium cv. Yuh Hwa rhizome explants. Through transfer experiments, it was determined that the commitment to shoot induction occurred between 10 and 14 days of exposure to at least 2.5 μM BA. BA when supplied at 20 μM during the fit 14 days of culture was found to be sufficient to induce shoot formation. Both shoot elongation and root formation were greatly improved by decreasing the BA concentration. By using radiolabelled BA, adenine was found to be a major metabolite in the rhizome tissue. Free IAA levels, quantitated by GC-MS, did not correlate well with the organogenesis of rhizomes, nor did the levels of free IAA correlate well with the activities of peroxidase and IAA oxidase, indicating a complex relationship between hormone concentration and differentiation.

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Xiaoling Yu and Barbara M. Reed

Multiplication and elongation of shoot cultures established from mature trees of hazelnut cvs. Nonpareil and Tonda Gentile Romana were affected by changes in basal medium, carbon source and concentration, cytokinin and agar concentration. Explants on DKW medium produced significantly more shoots than those on Anderson medium or modified woody plant medium for chestnut. Explants on DKW medium with 3% glucose or fructose gave more and longer shoots than those with the other carbon sources. Cytokinins 6 benzylaminopurine (BA) and zeatin were more effective in producing shoots than kinetin and 2iP. On BA supplemented medium, the best multiplication rate was obtained with 1.5 - 2.0 mg/l. Explants grown on 0.4% agar produced more shoots than those on 0.6%, however, prolonged culture on 0.4% agar caused vitrification of lower parts of the plants. Shoot multiplication rates of these two cultivars were similar, but `Nonpareil' produced longer shoots than `Tonda Gentile Romana'.

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Meriam G. Karlsson and Royal D. Heins

The relative progression of lateral shoot elongation from pinch to flower of chrysanthemum [Dendranthema grandiflora (Ramat.) Kitamura `Bright Golden Anne'] plants grown under 2 to 22 mol·day-1·m-2 photosynthetic photon flux and 10 to 20C was modeled using Richards function. Parameters for the function were determined by first transforming data of shoot length and time from pinch (start of short photoperiods) to flower to a relative scale of 0.0 to 1.0 by dividing all intermediate shoot lengths and measurement dates by final shoot length and number of days to flower, respectively. Data used for parameter estimation originated with plants grown at a daily average of ≤20C, since those grown at a daily average above 20C exhibited delayed morphological flower induction and reached 50% of the final shoot length earlier in development. Relative shoot elongation was described by Richards function in the following form: Relative shoot length = SF × {1 + [(SF/SO)N-1] e-SF Kt}-1/N where t (relative time) = 0.0 to 1.0, SF (maximum relative shoot length) = 1.018, SO (relative shoot length at t = o) = 0.0131, N (model parameter related to the shape of the curve) =0.3923, and K (model parameter related to mean relative growth rate) = 5.8138.

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Michael A. Arnold and Eric Young

After receiving 0, 600, 1200, or 1800 hr. of chilling at 5C, one-year-old Malus domestica Borkh. seedlings were given 10 sec. root dips either 10,000 ppm K-IBA solution or water control. Following chilling and IBA treatments, 20 seedlings of each combination were placed in forcing conditions of 20 ± 2C root temperatures and either 20 or 5 ± 1C shoot temperatures. Five seedlings of each treatment were harvested after 0, 7, 14, and 21 days of forcing. Five C prohibited budbreak and bark slipage for up to 21 days. Under 20C, budbreak, shoot elongation and root growth all occurred earlier, faster, and reached a higher level with increased chilling. Twenty C root and 5C shoot temperatures during forcing resulted in large increases in the growth of adventitious shoots on lateral roots, but had little effect on the formation of adventitious shoots on the tap root. K-IBA prohibited development of adventitious shoots on roots, reduced shoot elongation more so than budbreak, and increased root regeneration across chilling hours. K-IBA inhibition of adventitious shoots did not alter the overall pattern of root regeneration enhancement by chilling.

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Michael A. Arnold and Eric Young

After receiving 0, 600, 1200, or 1800 hr. of chilling at 5C, one-year-old Malus domestica Borkh. seedlings were given 10 sec. root dips either 10,000 ppm K-IBA solution or water control. Following chilling and IBA treatments, 20 seedlings of each combination were placed in forcing conditions of 20 ± 2C root temperatures and either 20 or 5 ± 1C shoot temperatures. Five seedlings of each treatment were harvested after 0, 7, 14, and 21 days of forcing. Five C prohibited budbreak and bark slipage for up to 21 days. Under 20C, budbreak, shoot elongation and root growth all occurred earlier, faster, and reached a higher level with increased chilling. Twenty C root and 5C shoot temperatures during forcing resulted in large increases in the growth of adventitious shoots on lateral roots, but had little effect on the formation of adventitious shoots on the tap root. K-IBA prohibited development of adventitious shoots on roots, reduced shoot elongation more so than budbreak, and increased root regeneration across chilling hours. K-IBA inhibition of adventitious shoots did not alter the overall pattern of root regeneration enhancement by chilling.

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N. Bernstein, A. Meiri, and M. Zilberstaine

In most crop species, growth of the shoot is more sensitive to salt stress than root growth. Avocado [Persea americana Mill.] is very sensitive to NaCl stress. Even low concentrations of salt (15 mm) inhibit tree growth and decrease productivity. Observations in experimental orchards have suggested that root growth in avocado might be more restricted by salinity than shoot growth. In the present study, we evaluated quantitatively the inhibitory effects of salt stress on growth of the avocado root in comparison to the shoot. Seedling plants of the West-Indian rootstock `Degania 117' were grown in complete nutrient solution containing 1, 5, 15, or 25 mm NaCl. The threshold NaCl concentration causing root and shoot growth reduction occurred between 5 and 15 mm. At all concentrations, root growth was much more sensitive to salinity than shoot growth. A concentration of 15 mm NaCl, which did not affect the rate of leaf emergence on the plant and decreased leaf biomass production only 10%, induced a 43% reduction in the rate of root elongation and decreased root volumetric growth rate by 33%. Under 25 mm NaCl, leaf biomass production, leaf initiation rate and leaf elongation rate were reduced 19.5%, 12%, and 5%, respectively, while root volumetric growth and root elongation rate were reduced 65% and 75%, respectively. This strong root growth inhibition is expected to influence the whole plant and therefore root growth under salinity should be considered as an important criterion for rootstocks' tolerance to NaCl.

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Yrina P. Ferreras and Harry Jan Swartz

Shoot proliferation of Acer ginnala Maxim. (Amur maple) from nodal-segments was obtained on Murashige and Skoog salts and vitamins supplemented with 25 nM thidiazuron and 3% sucrose. Higher concentrations of cytokinin resulted in callus formation at the base of explants. Explant orientation had a significant effect on shoot elongation. Explant elongation and proliferation were correlated. Plants inverted in the medium elongated and proliferated readily. Branching was obtained primarily from axillary buds several nodes basal to the apex. Gelling agent type did not affect proliferation. Vitrification was significantly affected by type of gelling agent, gelling agent concentration and thidiazuron concentration. In vitro shoots rooted readily even in medium containing adenine. Greater than 95% of the in vitro plants established in the greenhouse.