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'Who's who' in two different flower types of Calluna vulgaris (Ericaceae): morphological and molecular analyses of flower organ identity.

Borchert T, Eckardt K, Fuchs J, Krüger K, Hohe A - BMC Plant Biol. (2009)

Bottom Line: Organ identity in both wild-type and 'bud-flowering' C. vulgaris was clarified using a combination of microscopic and molecular methods.Our results for bract, sepal and petal organ identity are supported by the 'ABCDE model'.However, loss of stamens in the 'bud-flowering' phenotype is an exceptional flower organ modification that cannot be explained by modified spatial expression of known organ identity genes.

View Article: PubMed Central - HTML - PubMed

Affiliation: Institute of Vegetable and Ornamental Crops (IGZ), Department Plant Propagation, Kuehnhaeuser Str 101, 99189 Erfurt, Germany. hohe@erfurt.igzev.de. borchert@erfurt.igzev.de

ABSTRACT

Background: The ornamental crop Calluna vulgaris is of increasing importance to the horticultural industry in the northern hemisphere due to a flower organ mutation: the flowers of the 'bud-flowering' phenotype remain closed i.e. as buds throughout the total flowering period and thereby maintain more colorful flowers for a longer period of time than the wild-type. This feature is accompanied and presumably caused by the complete lack of stamens. Descriptions of this botanical particularity are inconsistent and partially conflicting. In order to clarify basic questions of flower organ identity in general and stamen loss in detail, a study of the wild-type and the 'bud-flowering' flower type of C. vulgaris was initiated.

Results: Flowers were examined by macro- and microscopic techniques. Organ development was investigated comparatively in both the wild-type and the 'bud-flowering' type by histological analyses. Analysis of epidermal cell surface structure of vegetative tissues and perianth organs using scanning electron microscopy revealed that in wild-type flowers the outer whorls of colored organs may be identified as sepals, while the inner ones may be identified as petals. In the 'bud-flowering' type, two whorls of sepals are directly followed by the gynoecium. Both, petals and stamens, are completely missing in this flower type. The uppermost whorl of green leaves represents bracts in both flower types. In addition, two MADS-box genes (homologs of AP3/DEF and SEP1/2) were identified in C. vulgaris using RACE-PCR. Expression analysis by qRT-PCR was conducted for both genes in leaves, bracts, sepals and petals. These experiments revealed an expression pattern supporting the organ classification based on morphological characteristics.

Conclusions: Organ identity in both wild-type and 'bud-flowering' C. vulgaris was clarified using a combination of microscopic and molecular methods. Our results for bract, sepal and petal organ identity are supported by the 'ABCDE model'. However, loss of stamens in the 'bud-flowering' phenotype is an exceptional flower organ modification that cannot be explained by modified spatial expression of known organ identity genes.

Show MeSH
Flower types of C. vulgaris. A: wild-type (Niederohe from Lueneburger Heide, Germany). B: 'bud-flowering' ('Amethyst'); C: bottom of wild-type (Niederohe from Lueneburger Heide, Germany) flower; Labels are: car (carpels), sta (stamens), ugl (uppermost whorls of green leaves). The bipartites perianth is separated in whorl I and whorl II organs.
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Figure 1: Flower types of C. vulgaris. A: wild-type (Niederohe from Lueneburger Heide, Germany). B: 'bud-flowering' ('Amethyst'); C: bottom of wild-type (Niederohe from Lueneburger Heide, Germany) flower; Labels are: car (carpels), sta (stamens), ugl (uppermost whorls of green leaves). The bipartites perianth is separated in whorl I and whorl II organs.

Mentions: Calluna vulgaris L. (Hull.) (Fig. 1A) belongs to the order Ericales, which comprises 25 families including 346 genera with more than 11,500 species in total [1]. The Ericales incorporate about 5.9% of core eudicot diversity, one third of which is made up of the Ericaceae alone [1]. The economic significance of C. vulgaris to the horticultural industry in Europe and North-America is continually increasing [2]. The current market share in Germany for instance, amounts to approximately 141 million EUR, or > 100 million plants per year, respectively [2]. In principal, this economic significance is the results of a single but considerable change in the flower morphology: the loss of stamens that is accompanied by a non-opening of the flower bud. In contrast to wild-type flowers (Fig. 1A) that are only attractive from August to October the resulting 'bud-flowering' phenotype (Fig. 1B) preserves its unpollinated stigmas within the never-opening buds and has an extended flowering period up to December. For this reason, it is the most valuable flower type of this species to the horticultural business. In contrast, other forms, such as the 'filled' or the 'multi-bracteate' types are less important. Previous investigations revealed the monogenic recessive inheritance of the 'bud-flowering' trait [3] that was described in literature for the first time (as far as known by the authors) in 1935 [4].


'Who's who' in two different flower types of Calluna vulgaris (Ericaceae): morphological and molecular analyses of flower organ identity.

Borchert T, Eckardt K, Fuchs J, Krüger K, Hohe A - BMC Plant Biol. (2009)

Flower types of C. vulgaris. A: wild-type (Niederohe from Lueneburger Heide, Germany). B: 'bud-flowering' ('Amethyst'); C: bottom of wild-type (Niederohe from Lueneburger Heide, Germany) flower; Labels are: car (carpels), sta (stamens), ugl (uppermost whorls of green leaves). The bipartites perianth is separated in whorl I and whorl II organs.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2803492&req=5

Figure 1: Flower types of C. vulgaris. A: wild-type (Niederohe from Lueneburger Heide, Germany). B: 'bud-flowering' ('Amethyst'); C: bottom of wild-type (Niederohe from Lueneburger Heide, Germany) flower; Labels are: car (carpels), sta (stamens), ugl (uppermost whorls of green leaves). The bipartites perianth is separated in whorl I and whorl II organs.
Mentions: Calluna vulgaris L. (Hull.) (Fig. 1A) belongs to the order Ericales, which comprises 25 families including 346 genera with more than 11,500 species in total [1]. The Ericales incorporate about 5.9% of core eudicot diversity, one third of which is made up of the Ericaceae alone [1]. The economic significance of C. vulgaris to the horticultural industry in Europe and North-America is continually increasing [2]. The current market share in Germany for instance, amounts to approximately 141 million EUR, or > 100 million plants per year, respectively [2]. In principal, this economic significance is the results of a single but considerable change in the flower morphology: the loss of stamens that is accompanied by a non-opening of the flower bud. In contrast to wild-type flowers (Fig. 1A) that are only attractive from August to October the resulting 'bud-flowering' phenotype (Fig. 1B) preserves its unpollinated stigmas within the never-opening buds and has an extended flowering period up to December. For this reason, it is the most valuable flower type of this species to the horticultural business. In contrast, other forms, such as the 'filled' or the 'multi-bracteate' types are less important. Previous investigations revealed the monogenic recessive inheritance of the 'bud-flowering' trait [3] that was described in literature for the first time (as far as known by the authors) in 1935 [4].

Bottom Line: Organ identity in both wild-type and 'bud-flowering' C. vulgaris was clarified using a combination of microscopic and molecular methods.Our results for bract, sepal and petal organ identity are supported by the 'ABCDE model'.However, loss of stamens in the 'bud-flowering' phenotype is an exceptional flower organ modification that cannot be explained by modified spatial expression of known organ identity genes.

View Article: PubMed Central - HTML - PubMed

Affiliation: Institute of Vegetable and Ornamental Crops (IGZ), Department Plant Propagation, Kuehnhaeuser Str 101, 99189 Erfurt, Germany. hohe@erfurt.igzev.de. borchert@erfurt.igzev.de

ABSTRACT

Background: The ornamental crop Calluna vulgaris is of increasing importance to the horticultural industry in the northern hemisphere due to a flower organ mutation: the flowers of the 'bud-flowering' phenotype remain closed i.e. as buds throughout the total flowering period and thereby maintain more colorful flowers for a longer period of time than the wild-type. This feature is accompanied and presumably caused by the complete lack of stamens. Descriptions of this botanical particularity are inconsistent and partially conflicting. In order to clarify basic questions of flower organ identity in general and stamen loss in detail, a study of the wild-type and the 'bud-flowering' flower type of C. vulgaris was initiated.

Results: Flowers were examined by macro- and microscopic techniques. Organ development was investigated comparatively in both the wild-type and the 'bud-flowering' type by histological analyses. Analysis of epidermal cell surface structure of vegetative tissues and perianth organs using scanning electron microscopy revealed that in wild-type flowers the outer whorls of colored organs may be identified as sepals, while the inner ones may be identified as petals. In the 'bud-flowering' type, two whorls of sepals are directly followed by the gynoecium. Both, petals and stamens, are completely missing in this flower type. The uppermost whorl of green leaves represents bracts in both flower types. In addition, two MADS-box genes (homologs of AP3/DEF and SEP1/2) were identified in C. vulgaris using RACE-PCR. Expression analysis by qRT-PCR was conducted for both genes in leaves, bracts, sepals and petals. These experiments revealed an expression pattern supporting the organ classification based on morphological characteristics.

Conclusions: Organ identity in both wild-type and 'bud-flowering' C. vulgaris was clarified using a combination of microscopic and molecular methods. Our results for bract, sepal and petal organ identity are supported by the 'ABCDE model'. However, loss of stamens in the 'bud-flowering' phenotype is an exceptional flower organ modification that cannot be explained by modified spatial expression of known organ identity genes.

Show MeSH