QUICK SEARCH:   [advanced] Author: Keyword(s):
Home     Help     Feedback     Subscriptions     Archive     Search     Table of Contents

This Article Summary Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Efremova, N. Articles by Schwarz-Sommer, Z. Search for Related Content PubMed PubMed Citation Articles by Efremova, N. Articles by Schwarz-Sommer, Z.

Epidermal control of floral organ identity by class B homeotic genes in Antirrhinum and Arabidopsis

Max-Planck Institut für Züchtungsforschung, Carl-von-Linné Weg 10, 50289 Köln, Germany

View larger version (85K): [in a new window]   Fig. 1. Morphological features of Antirrhinum flowers: (left panels) wild-type; (middle panels) def; (right panels) def; AFI::DEF. (A-C) Photographs of whole mature flowers. The arrow in C indicates the shortened style of carpeloid third whorl organs (for comparison see the third whorl carpel in B). Bars, 5 mm. D-I: SEM micrographs of the inner (adaxial) epidermal surface of the upper (D-F) and the lower (G-I) regions of the second whorl organs. Bar, 20 µm. (J-L) Cross sections taken approximately in the middle of immature buds. Arrows in K and L point to the organ in the dorsal position in whorl 3, that is retarded in growth and is not visible in this section in wild-type (J) and transgenic flowers (L), but develops fully as a carpeloid organ in def mutant flowers (K). The flower in L, in contrast to the flower in C, did not develop a central carpel. Bar, 1 mm. (M-O) Cellular morphology of first- and second whorl organs in cross sections shown at a higher magnification. The shape and size of sub-epidermal cells in the transgenic second whorl organs in O is intermediate between the large and irregularly shaped sub-epidermal cells in whorl 2 of def mutants (N) and the small and more isometric sub-epidermal cells in wild-type petals (M). Bar, 100 µm. Numbers indicate whorls.

View larger version (28K): [in a new window]   Fig. 2. Schematic summary of experimental observations on the influence of epidermal B function on petal development in Antirrhinum. Autonomous control is indicated by the solid arrows and non-autonomous control is shown by the broken arrows. The contribution of the endogenous DEF/GLO genes in wild-type sepals is indicated in red. All other control events are common to AFI::DEF/GLO wild-type sepals and def (or glo) mutant petals expressing AFI::DEF (or AFI::GLO). The dotted arrows on the right indicate an epidermal influence on petal shape and size, which are also affected by sub-epidermal events (Perbal et al., 1996), not discussed in this report.

View larger version (127K): [in a new window]   Fig. 3. In situ analysis of DEF (A,B) and GLO (C,D) expression in longitudinal sections of def; AFI::DEF (A,B) and glo; AFI::GLO (C,D) flowers. The hybridisation signal is confined to the outermost cell layer in young flowers (A,C) and in older petals (B,D). The sections were stained with calcofluor and the hybridisation signal appears as a purple stain in fluorescent light. Bars,100 µm. Numbers indicate whorls.

View larger version (51K): [in a new window]   Fig. 4. Morphological features of Antirrhinum flowers that express the AFI::DEF/GLO transgenes in a wild-type background. (A-D) Mature flowers displaying various first whorl organ transformations. (A) Lateral view of flower with slightly aberrant petals (pet). (B-D) Frontal view of flowers, with some organs (all petals in B, all petals and stamens in C and all inner organs in D) removed. An anomalous carpel is shown in C. For comparison, B shows a wild-type carpel developing in a flower with a severe first whorl transformation. The position of the dorsal (d), lateral (l) and ventral (v) sepals are indicated. (E,F) SEM of inner epidermal cells within the lobe (E) and tube (F) regions of a petaloid sepal. Bars, 20 µm. (G,H) Expression pattern of DEF (G) and GLO (H) in sequential cross sections from a first whorl organ. The weak sub-epidermal hybridisation signal within the marginal region is most obvious around vascular bundles. Epidermal expression is present in this, and in the adjacent, region. Bars, 200 µm.

View larger version (84K): [in a new window]   Fig. 5. Phenotypes of wild-type (A), AFI::DEF/GLO (B), ap3 (C) and ap3; AFI::DEF (D,E) Arabidopsis flowers. In E a sepal has been removed to reveal immature petals and stamens. Incomplete suppression of sub-epidermal chlorophyll synthesis by the epidermal transgenes in the petaloid first whorl of wild-type flowers (B) and in the second whorl of ap3 mutant flowers (D,E) is revealed by the slightly green colour of the organs compared to the white colour of mature petals (A,B). Note the immature stamens in the centre of AFI::DEF/GLO flowers in B (viewed by SEM in Fig. 7D) and immature petals and stamens in the ap3; AFI::DEF flowers in D and E (viewed by SEM in Fig. 6C).

View larger version (136K): [in a new window]   Fig. 6. Morphological features of Arabidopsis flowers: (left panels) wild type; (middle panels) ap3; (right panels) ap3; AFI::DEF viewed by SEM. (A-C) Overall morphology of young flowers. Some of the sepals and petals in the front have been removed. The arrow in C indicates a wild-type-like stamen in the transgenic flower. Bars,100 µm. (D-I) Outer (D-F) and inner (G-I) epidermal surfaces of second whorl organs. Bars, 20 µm. (J-L) Cross sections taken approximately in the middle of immature buds. Note the similarity of sub-epidermal petal cells (in whorl 2), and the presence of pollen in stamens (in whorl 3), in wild type (J) and in ap3; AFI::DEF (L). Bars, 100 µm. Numbers indicate the whorl.

View larger version (135K): [in a new window]   Fig. 7. SEM micrographs of Arabidopsis flowers expressing epidermal transgenes in a wild-type background. Strong (B,D) and weak (A,C) phenotypes are shown for the AFI::DEF (A,B) and AFI::DEF/GLO (C,D) transgenes. In A-D some or all first whorl organs were removed. Note the differences in shape and surface structure between first whorl organs in B and D. The flowers with wild-type sepals in E indicate that AFI::GLO has no effect when expressed alone; in contrast, expression of the FDH::PI transgene results in transformation of aberrant sepal/petal mosaic organs. Bars, 50 µm.

View larger version (174K): [in a new window]   Fig. 8. Expression of DEF (A-C), AP3 (D) and PI (E,F) mRNAs in Arabidopsis inflorescences and flowers doubly transgenic for the AFI::DEF/GLO (A-E) and FDH::AP3/PI (F) transgenes. (A-C) Epidermal expression of the AFI::DEF transgene in differentiating organs of very young (A) and older (B,C) flowers. Bars, 100 µm. (C-F) The region encompassing the first and second whorl organs of older AFI::DEF/GLO (C-E) and FDH::AP3/PI flowers (F) shown at higher magnification. Bars, 200 µm. Endogenous epidermal AP3 (D) and PI (E) expression is not detectable in AFI::DEF/GLO first whorl organs and PI mRNA is not found in sub-epidermal cells in first whorl organs in FDH::AP3/PI flowers (F). Sections were viewed under bright-field illumination. Numbers indicate the whorl.