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Peter M Hirst and David C Ferree

Floral development was studied in buds of `Starkspur Supreme Delicious' apple trees growing on B.9, M.26 EMLA, M.7 EMLA, P.18, and seedling rootstocks. In each of 3 years, buds were sampled from the previous years growth at intervals throughout the growing season and dissected to determine whether the apex was domed, indicating the start of floral development. Number of bud scales and true leaves increased during the early part of the growing season, but remained fairly constant beyond 70 days after full bloom. The type of rootstock did not affect the number of bud scales or transition leaves, and effects on true leaf numbers were small and inconsistent. Final bract number per floral bud was similarly unaffected by rootstock. The proportion of buds in which flowers were formed was influenced by rootstock in only one year of the study, which was characterized by high temperatures and low rainfall over the period of flower formation. Bracts were observed only in floral buds, and became visible after doming of bud apices had occurred. Flowers were formed during the first 20 days in August, regardless of rootstock or year. The appendage number of vegetative buds was constant from 70 days after full bloom until the end of the growing season, but the number of appendages in floral buds increased due to the continued production of bracts. The critical bud appendage number for `Starkspur Supreme Delicious' before flower formation was 20, and was stable among rootstocks and years. Buds with diameters above 3.1 mm were generally floral, but on this basis only 65% of buds could be correctly classified. Spur leaf number, spur leaf area, and spur leaf dry weight were not good predictors of floral formation within the spur bud.

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Meriam G. Karlsson and Janice T. Hanscom

The progression of flower initiation was documented in Dendranthema X grandiflorum (Ramat) Kitamura `Bright Golden Anne'. Rooted cuttings were planted and grown under 16 hours photoperiod (360 μmol·s-1m-2) and a constant 20C. After 7 days, the plants were pinched, the temperature reduced to 5, 10 or 15C and the day length shortened to 10 hours (13 mol·day-1m-2). Scanning electron microscopy was used to determine the transition from vegetative to reproductive meristem and to document the flower formation process. Shoot apices from three randomly selected plants were dissected weekly from each temperature until plants had developed floret primordia to completely cover the apical dome. Delayed floral development in the low temperature grown plants was a combination of a later flower initiation event and a slower progression of flower development. Required time for formation of 3-4 rows with floret primordia was about 21 days at 15C, 32 days at 10C and 70 days at 5C.

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Jennifer K. Hart and David J. Hannapel

Homeobox genes contain sequences coding for DNA-binding motifs. These sequences are highly conserved across both the animal and plant kingdoms. Members of this gene family code for transcription factors that are key regulators of developmental organization. In an attempt to further elucidate the developmental process of tuberization in the potato plant, a full-length homeobox cDNA has been isolated via sequence homology from an early tuberization stage cDNA library constructed from 4-day axillary bud tubers. This cDNA, POTH1, has been sequenced and characterized by Southern blotting, northern analysis, sequence comparison, and in situ hybridization. POTH1 is shown to be a class I homeobox gene with 45% overall similarity to Kn-1 of maize and 73% match in the homeobox region. Messenger RNA accumulation studies indicate that POTH1 mRNA, unlike most homeobox transcripts, is not limited to a particular organ or developmental stage. Instead, POTH1 mRNA accumulates in rapidly growing cells of the potato plant: the apical meristems, the vascular cambium, the edges of young leaves, axillary buds, and root tips. In situ studies indicate accumulation of POTH1 mRNA in the tunica and corpus layers of the apical dome of the shoot apex and the stolon apex. In the stolon, growth and proliferation of the parenchymal cells associated with the vascular cambium contribute to swelling during early stages of tuberization, and this tissue accumulates POTH1 mRNA. It is possible that POTH1 may be posttranscriptionally regulated in a particular organ or stage of growth, or that it is involved in a wider range of growth processes than most plant homeobox genes.

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Hisanao Suzue, Munetaka Hosokawa, and Susumu Yazawa

, S. Goi, M. Tanaka, M. 1994 The chimeric structure of the apical dome of chrysanthemum [ Dendranthema grandiflorum (Ramat.) Kitam.] is affected by cryopreservation Scientia Hort. 57 347 351 Hosokawa, M

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Adam Dale, Becky R. Hughes, and Danielle Donnelly

of thermotherapy (heat treatment) are the key factors in virus elimination ( Belkengren and Miller, 1962 ). Researchers generally use the term “meristem tip culture” when the dissected portion of the shoot is <1.0 mm in length with an apical dome and

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Karen R. Harris-Shultz, Brian M. Schwartz, and Jeff A. Brady

: Effect of dissection to expose the apical dome Plant Sci. 130 217 225 Thompson, M.M. Olmo, H.P. 1963 Cytohistological studies of cytochimeric and tetraploid grapes Amer. J. Bot. 50 901 906 Wang, Z. Wu, Y. Martin, D.L. Gao, H. Samuels, T. Tan, C. 2010

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Juanxu Liu, Min Deng, Richard J. Henny, Jianjun Chen, and Jiahua Xie

organogenesis from a stem explant of Dracaena surculosa ‘Florida Beauty’. ( A ) A shoot apical dome was formed from callus with vascular connection to stem explant (pointed by an arrow). ( B ) Differentiation of apical meristem led to appearance of young

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Jane Kahia, Margaret Kirika, Hudson Lubabali, and Sinclair Mantell

total number of embryos was the combined summation of somatic embryos at different stages (as described below) of development in each culture. Globular stage. Discrete round structures with no visible cotyledons or apical dome originating and projecting

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William R. Okie and Bryan Blackburn

into the active form, P fr ( Smith, 2000 ). Bud scales are known to filter the light that reaches the apical dome ( Pukacki et al., 1980 ; Pukacki and Giertych, 1982 ). Peach has been little studied in this regard, but Solymosi and Boddi (2006

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James S. Busse, Senay Ozgen, and Jiwan P. Palta

.8 μM Ca ( D ) medium appear normal. Leaf primordia (P) are found on the flank of the apical dome (bar = 50.0 μm). The shoot apical meristem showed no differences when shoots were cultured on sufficient ( Fig. 2C ) or suboptimal ( Fig. 2D