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Carole H. Saravitz, Frank A. Blazich, and Henry V. Amerson

Hypocotyl cuttings were prepared from Ii-week-old aseptically grown seedlings of Fraser fir [Abies fraseri (Pursh) Poir.] and cultured 18 days on media containing 0 to 40 mg IBA/liter followed by transfer to the same medium without auxin. Greatest rooting (66%) occurred after treatment with 20 mg IBA/liter, whereas the greatest number of roots per rooted cutting (7.4) was noted following treatment with 40 mg·liter-1. Chemical name used: 1H-indole-3-butyric acid (IBA).

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Jing-Tian Ling, Henock Zerit, and Roger J. Sauve

Seeds of Chinese elm cultivar King's Choice were collected from field-grown plants and germinated aseptically. Hypocotyl segments were excised from 2-week-old seedlings and cultured on Murashige and Skoog (MS) medium supplemented with TDZ alone or in combination with 0.05 mg/L NAA. At least 50% of explants produced shoots 4 weeks after culture initiation. At thidiazuron (TDZ) from 0.05 to 5.0 mg/L, the number of shoots/explant increased as concentration increased. Addition of 0.05 mg/L NAA stimulated shoot regeneration when TDZ concentration was 0.5 mg/L or less, but suppressed it if TDZ concentration was higher than 0.5 mg/L. Regenerated shoots elongated quickly on MS medium supplemented with 1 mg/L gibberellic acid and initiated rooting on MS medium containing 0.1 mg/L indole-3-butyric acid.

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Mohsen Hesami and Mohammad Hosein Daneshvar

from immature hypocotyls of F. religiosa . Studies about in vitro regeneration of the Moraceae family ( Bayoudh et al., 2015 ; Sharma et al., 2015 ) have mainly focused on the formation of shoots. According to this study, we introduce efficient

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Grete Grindal Patil, Vibeke Alm, Roar Moe, and Olavi Junttila

The role of phytochrome in control of stem elongation by daily temperature alternations is unclear. The aim of this work was to study the involvement of phytochrome B in thermoperiodism in cucumber (Cucumis sativus L.), and the interaction with gibberellin (GA). The wild type and the phytochrome B deficient, long-hypocotyl (lh) cucumber mutant were grown under alternating day (DT) and night temperature (NT) and either with or without an exposure to end-of-day far-red light (EOD-FR). Without EOD-FR, hypocotyl and internodes of the wild type plants were shorter under a low DT (19 °C)/high NT (25 °C) (negative DIF) compared with a high DT/low NT regime (positive DIF), while the number of leaves was reduced by 12%. EOD-FR enhanced elongation of hypocotyl and internodes. However, EOD-FR reduced the effect of alternating temperature on hypocotyl elongation. The lh cucumber mutant did not respond to EOD-FR treatments, but internode length was slightly increased by positive compared with negative DIF. The results suggest that phytochrome B is required for a maximum effect of daily temperature alternations on stem elongation in cucumber. Additional GA4 reduced the difference between positive and negative DIF, but it had a minor effect only on the difference between EOD-FR and EOD red light (EOD-R) in the wild type. Plants depleted for endogenous GA by the GA biosynthesis inhibitor paclobutrazol, did not respond at all to DIF or EOD treatments. When seedlings were treated with prohexadione-calcium, which blocks both biosynthesis and inactivation of GA4, response to applied GA4 was enhanced by EOD-FR. The present results suggest that, in cucumber, EOD-FR, and probably also positive DIF, enhances tissue sensitivity to GA4. In addition, catabolism of GA4 can be enhanced by negative DIF.

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Carole H. Saravitz, Frank A. Blazich, and Henry V. Amerson

Hypocotyls of Fraser fir (Abies fraseri (Pursh) Poir.) were excised from seeds germination 9 days and placed on bud induction medium containing 10 mg/liter benzyladenine (BA) and 0.01 mg/liter naphthaleneacetic acid (NAA) or medium without growth regulators. After 3 days on medium containing growth regulators, cell divisions were localized in epidermal and subepidermal layers of the hypocotyl while similar cell divisions were not observed in control-treated hypocotyls. Cell clusters consisting of two to five cells were present after 7 days in hypocotyls placed on bud induction medium. In control-treated hypocotyls, stomata continued to develop and cells within the cortex became vacuolated during the first 2 weeks in culture. All hypocotyls were transferred to secondary medium after 3 weeks. Cell clusters continued to enlarge into meristemoids in hypocotyls initially placed on bud induction medium. Gradually, meristemoids developed into buds and cataphylls were observed covering bud meristems.

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Carole H. Saravitz, Frank A. Blazich, and Henry V. Amerson

Cotyledons and hypocotyls of Fraser fir [Abies fraseri (Pursh) Poir.] were excised from seeds treated with H2 O2 for 9 days and placed on bud induction medium containing 10 mg BA/liter and 0.01 mg NAA/liter or medium without growth regulators. Although adventitious buds did not develop, cotyledons exposed to growth regulators responded differently than cotyledons placed on medium lacking growth regulators. Cotyledons and hypocotyls responded similarly to growth regulators during the initial phase in culture, but cell divisions ceased in cotyledons, thus preventing meristemoid and subsequent bud development. After 3 days on medium containing growth regulators cell divisions were localized in epidermal and subjacent layers of hypocotyls, whereas similar cell divisions were' not observed in hypocotyls placed on medium without growth regulators. Cell clusters consisting of two to five cells (promeristemoids) were present after 7 days on hypocotyls placed on bud induction medium. In hypocotyls placed on medium without growth regulators, stomata continued to develop and cells within the cortex became vacuolated during the first 2 weeks in culture. All explants were transferred to secondary medium after 3 weeks. Cell clusters continued to enlarge into meristemoids on hypocotyls initially placed on bud induction medium. Gradually, meristemoids developed into buds and cataphylls were observed covering bud meristems. Chemical names used: N -(phenylmethyl)-1 H -purine-6-amine (BA), 1-naphthaleneacetic acid (NAA).

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Thomas Björkman

Brushing is an effective method to control hypocotyl elongation in cucumbers (Cucumis sativus L. `Turbo') grown in plug trays for transplanting. The amount of daily brushing and the number of days to brush for best performance was determined. Treatment with 10 strokes per day for the 4 days of maximal hypocotyl elongation was sufficient to reduce final hypocotyl length by 25%. More brushing did not meaningfully reduce elongation further. Inhibition of dry weight gain, which is detrimental, was minor (<10%) compared with the height control achieved. Despite seasonal differences in absolute elongation, the effects of brushing were the same.

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James S. Busse, Monica Figueroa-Cabanas, and Dennis P. Stimart*

Adventitious shoot formation in vitro from Antirrhinum majus L. hypocotyls was investigated using two inbred lines, the most and least regenerative lines selected from screening. Time course analysis indicated cell division in the most regenerative line occurred first in one or a small number of epidermal cells with periclinal and anticlinal divisions. Subsequently, cortical then vascular cells were recruited beneath the dividing epidermal cells. Once shoots formed, their vascular system was continuous with the original hypocotyl explant. The least regenerative line had no cell division directed toward organogenesis. Shoot formation on hypocotyls of A. majus was adventitious in origin, by direct organogenesis and genotype dependent.

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James S. Busse, M. Figueroa-Cabanas, and D.P. Stimart

Developmental anatomy of adventitious shoot formation in vitro from snapdragon (Antirrhinum majus L.) hypocotyls was investigated using two inbred lines, the most (R) and least (NR) regenerative lines selected from screening (Schroeder and Stimart, 1999). Time course analysis indicated cell division in the most regenerative line occurred first in one or a small number of epidermal cells with periclinal and anticlinal divisions within 2 days of placing hypocotyls on induction medium. Subsequently, cortical then vascular cells were recruited beneath the dividing epidermal cells. Once shoots formed, their vascular system was continuous with the original hypocotyl explant. The least regenerative line had no cell division directed towards organogenesis through 6 days. Shoot formation on snapdragon hypocotyls was adventitious in origin, by direct organogenesis and genotype dependent.

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Kenneth R. Schroeder and Dennis P. Stimart

Hypocotyls from Antirrhinum majus L. were excised at 2 weeks of age from seedlings grown under a 16-hour photoperiod or continuous darkness. Explants were cultured on modified Murashige-Skoog (MS) medium containing 0, 0.44, 2.22, 4.44, 8.88, or 44.4 μm BA to investigate adventitious shoot formation. Excised hypocotyls from eight commercial cultivars, three inbred lines, and an F1 hybrid between two of the inbreds were cultured on MS medium containing 2.22 μm BA to assess genotypic effects on adventitious shoot formation. The influence of seedling age was assessed by excising hypocotyls from seedlings at 6, 10, 14, 18, 22, 26, or 30 days. Optimal conditions for adventitious shoot formation on excised hypocotyls included: seedling growth in a lighted environment, use of hypocotyls from 10-day-old seedlings, and culture on medium containing 2.22 μm BA for 3 weeks. Under these conditions, up to a 5-fold improvement in number of shoots per hypocotyl over previous studies was achieved. Adventitious shoot formation was genotype-dependent and appeared to be a dominant trait. Chemical name used: N 6-benzyladenine (BA).