A morphological and quantitative characterization of early floral development in apple (Malus x domestica Borkh.).

Apple is an important crop and a focus of research worldwide. However, some aspects of floral commitment and morphogenesis remain unclear. A detailed characterization of bourse shoot apex development was undertaken to provide a framework for future genetic, molecular and physiological studies. Eight morphologically distinct stages of shoot apex development, prior to winter dormancy, were defined. Based on measurements of meristem diameter, two stages of vegetative development were recognized. Vegetative meristems were flat, and either narrow (stage 0) or broad (stage 1). Pronounced doming of the apex marked stage 2. During stage 3, the domed meristem initiated four to six lateral floral meristems and subtending bracts before converting to a terminal floral meristem (stage 4). The terminal floral meristem proceeded directly with bractlet and sepal initiation, while lateral floral meristems initiated bractlets (stage 5). Sepal initiation began on the basal lateral flower (stage 6) and continued in an acropetal direction until all floral meristems had completed sepal initiation (stage 7). In this study, only stage 0 and stage 7 apices were observed in dormant buds, indicating that stages 1-6 are transient. The results suggest that broadening of the apex (stage 1) is the first morphological sign of commitment to flowering.

[1]  G. An,et al.  Developmentally regulated expression of two MADS-box genes, MdMADS3 and MdMADS4, in the morphogenesis of flower buds and fruits in apple , 2000, Planta.

[2]  J. Bowman,et al.  Early flower development in Arabidopsis. , 1990, The Plant cell.

[3]  R. M. Fulford,et al.  The Morphogenesis of Apple Buds II. The Development of the Bud , 1966 .

[4]  L. C. Luckwill,et al.  The Effects of Daminozide and Gibberellic Acid on Flower Initiation, Growth and Fruiting of Apple cv Golden Delicious , 1979 .

[5]  T. Dickinson,et al.  Floral Ontogeny and Morphology in Subfamily Amygdaloideae T. & G. (Rosaceae) , 1999, International Journal of Plant Sciences.

[6]  D. Weigel,et al.  LEAFY controls floral meristem identity in Arabidopsis , 1992, Cell.

[7]  Steven E. Ruzin,et al.  Plant Microtechnique and Microscopy , 1999 .

[8]  J. Einset,et al.  RADIATION DAMAGE IN APPLE SHOOT APICES , 1959 .

[9]  R. Fulford.  The Morphogenesis of Apple BudsI. The Activity of the Apical Meristem , 1966 .

[10]  M. Wada,et al.  Apple has two orthologues of FLORICAULA/LEAFY involved in flowering , 2002, Plant Molecular Biology.

[11]  Cindy Gustafson-Brown,et al.  Molecular characterization of the Arabidopsis floral homeotic gene APETALA1 , 1992, Nature.

[12]  E. Coen,et al.  Inflorescence Commitment and Architecture in Arabidopsis , 1997, Science.

[13]  M. Freeling.  Patterns in plant development (2nd edn) , 1990 .

[14]  David C. Ferree,et al.  Rootstock Effects on the Flowering of `Delicious' Apple. I. Bud Development , 1995 .

[15]  T. Dickinson,et al.  Floral Ontogeny and Morphology in Subfamily Spiraeoideae Endl. (Rosaceae) , 1999, International Journal of Plant Sciences.

[16]  D Weigel,et al.  LEAFY expression and flower initiation in Arabidopsis. , 1997, Development.

[17]  R. M. Fulford,et al.  The Morphogenesis of Apple Buds III. The Inception of Flowers , 1966 .

[18]  G. An,et al.  Characterization of MdMADS2, a member of the SQUAMOSA subfamily of genes, in apple. , 1999, Plant physiology.

[19]  D. Weigel,et al.  Floral determination and expression of floral regulatory genes in Arabidopsis. , 1997, Development.

[20]  I. Brooking,et al.  Seasonal variation in the onset and duration of flower development in ‘Royal Gala’ apple buds , 2001 .

[21]  T. Steeves,et al.  Patterns in plant development: Subject index , 1972 .

[22]  M. Faust,et al.  Flower Bud Induction in Apple Trees: Internal Control and Differentiation , 2011 .

[23]  M. Wada,et al.  Expression Pattern of Homologues of Floral Meristem Identity Genes LFY and AP1 during Flower Development in Apple , 2000 .

[24]  C. Pratt.  Apple flower and fruit: morphology and anatomy , 1988 .