Double-flowered

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A double-flowered cultivar of Impatiens walleriana. Double impatiens.jpg
A double-flowered cultivar of Impatiens walleriana .

"Double-flowered" describes varieties of flowers with extra petals, often containing flowers within flowers. [1] [2] The double-flowered trait is often noted alongside the scientific name with the abbreviation fl. pl. (flore pleno, a Latin ablative form meaning "with full flower"). [3] The first abnormality to be documented in flowers, double flowers are popular varieties of many commercial flower types, including roses, camellias and carnations. In some double-flowered varieties all of the reproductive organs are converted to petals as a result, they are sexually sterile and must be propagated through cuttings. Many double-flowered plants have little wildlife value as access to the nectaries is typically blocked by the mutation. [4]

Contents

History

Double flowers are the earliest documented form of floral abnormality, first recognized more than two thousand years ago. [2] Theophrastus mentioned double roses in his Enquiry into Plants, written before 286 BC. Pliny also described double roses in 1st century BC. In China, double peonies were known and selected by around 750 AD, and around 1000 AD double varieties of roses were cultivated to form the China rose (one of the ancestors of modern hybrid tea roses). [5] Today, most cultivated rose varieties bear this double-flower trait.

Double-flowered Arabidopsis Arabidopsis mutants.jpg
Double-flowered Arabidopsis

Herbalists of the Renaissance recognized double flowers and began to cultivate them in their gardens Rembert Dodoens published a description of double flowers in 1568, and John Gerard created illustrations of many double flowers beside their wild-type counterparts in 1597. A double-flowered variety of Marsh Marigold was discovered and cultivated in Austria in the late 16th century, becoming a valued garden plant. [6]

The first documented double-flowered mutant of Arabidopsis , a model organism for plant development and genetics, was recorded in 1873. [7] The mutated gene likely responsible for the phenotype, AGAMOUS, was cloned and characterized in 1990 in Elliot Meyerowitz's lab as part of his study of molecular mechanisms of pattern formation in flowers. [8]

Genetics of double-flower mutations

ABC model of flower development. Double flower varieties often arise from mutations affecting C class genes. ABC flower development.svg
ABC model of flower development. Double flower varieties often arise from mutations affecting C class genes.

Double-flower forms often arise when some or all of the stamens in a flower are replaced by petals. These types of mutations, where one organ in a developing organism is replaced with another, are known as homeotic mutations. They are usually recessive, although the double flower mutation in carnations exhibits incomplete dominance. [9]

In Arabidopsis , which has been used as a model for understanding flower development, the double-flower gene AGAMOUS encodes a protein responsible for tissue specification of stamen and carpel flower segments. When both copies of the gene are deleted or otherwise damaged, developing flowers lack the signals to form stamen and carpel segments. Regions which would have formed stamens instead default to petals and the carpel region develops into a new flower, resulting in a recursive sepal-petal-petal pattern. Because no stamens and carpels form, the plants have no reproductive organs and are sexually sterile.

Mutations affecting flower morphology in Arabidopsis can be described by the ABC model of flower development. In this model, genes involved in flower formation belong to one of three classes of genes: A class genes which affect sepal and petal formation, B class genes which affect petal and stamen formation, and C class genes which affect stamen and carpel formation. These genes are expressed in certain regions of the developing flower and are responsible for development of organs in those regions. Agamous is a C class gene, a transcription factor responsible for activating genes involved in stamen and carpel development.

Related Research Articles

<i>Arabidopsis thaliana</i> Model plant species in the family Brassicaceae

Arabidopsis thaliana, the thale cress, mouse-ear cress or arabidopsis, is a small flowering plant native to Eurasia and Africa. A. thaliana is considered a weed; it is found along the shoulders of roads and in disturbed land.

<i>Camellia</i> Genus of flowering plants in the tea family Theaceae

Camellia is a genus of flowering plants in the family Theaceae. They are found in eastern and southern Asia, from the Himalayas east to Japan and Indonesia. There are 100–300 described species, with some controversy over the exact number. There are also around 3,000 hybrids. The genus was named by Linnaeus after the Jesuit botanist Georg Joseph Kamel, who worked in the Philippines and described a species of camellia.

Stamen The male organ of a flower

The stamen is the pollen-producing reproductive organ of a flower. Collectively the stamens form the androecium.

Meristem Type of plant tissue involved in cell proliferation

The meristem is a type of tissue found in plants. It consists of undifferentiated cells capable of cell division. Cells in the meristem can develop into all the other tissues and organs that occur in plants. These cells continue to divide until a time when they get differentiated and then lose the ability to divide.

Peony Genus of flowering plants in the family Ranunculaceae

The peony or paeony is a flowering plant in the genus Paeonia, the only genus in the family Paeoniaceae. Peonies are native to Asia, Europe and Western North America. Scientists differ on the number of species that can be distinguished, ranging from 25 to 40, although the current consensus is 33 known species. The relationships between the species need to be further clarified.

Gynoecium The female organs of a flower

Gynoecium is most commonly used as a collective term for the parts of a flower that produce ovules and ultimately develop into the fruit and seeds. The gynoecium is the innermost whorl of a flower; it consists of pistils and is typically surrounded by the pollen-producing reproductive organs, the stamens, collectively called the androecium. The gynoecium is often referred to as the "female" portion of the flower, although rather than directly producing female gametes, the gynoecium produces megaspores, each of which develops into a female gametophyte which then produces egg cells.

ABC model of flower development Model for genetics of flower development

The ABC model of flower development is a scientific model of the process by which flowering plants produce a pattern of gene expression in meristems that leads to the appearance of an organ oriented towards sexual reproduction, a flower. There are three physiological developments that must occur in order for this to take place: firstly, the plant must pass from sexual immaturity into a sexually mature state ; secondly, the transformation of the apical meristem's function from a vegetative meristem into a floral meristem or inflorescence; and finally the growth of the flower's individual organs. The latter phase has been modelled using the ABC model, which aims to describe the biological basis of the process from the perspective of molecular and developmental genetics.

<i>Paeonia lactiflora</i> Species of flowering plant

Paeonia lactiflora is a species of herbaceous perennial flowering plant in the family Paeoniaceae, native to central and eastern Asia from eastern Tibet across northern China to eastern Siberia.

Phyllody Abnormal development of floral parts into leafy structures

Phyllody is the abnormal development of floral parts into leafy structures. It is generally caused by phytoplasma or virus infections, though it may also be because of environmental factors that result in an imbalance in plant hormones. Phyllody causes the affected plant to become partially or entirely sterile, as it is unable to normally produce flowers.

Flower Part of a plant

A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants. The biological function of a flower is to facilitate reproduction, usually by providing a mechanism for the union of sperm with eggs. Flowers may facilitate outcrossing resulting from cross-pollination or allow selfing when self-pollination occurs.

The MADS box is a conserved sequence motif. The genes which contain this motif are called the MADS-box gene family. The MADS box encodes the DNA-binding MADS domain. The MADS domain binds to DNA sequences of high similarity to the motif CC[A/T]6GG termed the CArG-box. MADS-domain proteins are generally transcription factors. The length of the MADS-box reported by various researchers varies somewhat, but typical lengths are in the range of 168 to 180 base pairs, i.e. the encoded MADS domain has a length of 56 to 60 amino acids. There is evidence that the MADS domain evolved from a sequence stretch of a type II topoisomerase in a common ancestor of all extant eukaryotes.

Superman is a plant gene in Arabidopsis thaliana, that plays a role in controlling the boundary between stamen and carpel development in a flower. It is named for the comic book character Superman, and the related genes kryptonite (gene) and clark kent were named accordingly. It encodes a transcription factor. Homologous genes are known in the petunia and snapdragon, which are also involved in flower development, although in both cases there are important differences from the functioning in Arabidopsis. Superman is expressed early on in flower development, in the stamen whorl adjacent to the carpel whorl. It interacts with the other genes of the ABC model of flower development in a variety of ways.

Apetala 2 Protein in Arabidopsis

Apetala 2(AP2) is a gene and a member of a large family of transcription factors, the AP2/EREBP family. In Arabidopsis thaliana AP2 plays a role in the ABC model of flower development. It was originally thought that this family of proteins was plant-specific; however, recent studies have shown that apicomplexans, including the causative agent of malaria, Plasmodium falciparum encode a related set of transcription factors, called the ApiAP2 family.

Evolutionary developmental biology (evo-devo) is the study of developmental programs and patterns from an evolutionary perspective. It seeks to understand the various influences shaping the form and nature of life on the planet. Evo-devo arose as a separate branch of science rather recently. An early sign of this occurred in 1999.

Important structures in plant development are buds, shoots, roots, leaves, and flowers; plants produce these tissues and structures throughout their life from meristems located at the tips of organs, or between mature tissues. Thus, a living plant always has embryonic tissues. By contrast, an animal embryo will very early produce all of the body parts that it will ever have in its life. When the animal is born, it has all its body parts and from that point will only grow larger and more mature. However, both plants and animals pass through a phylotypic stage that evolved independently and that causes a developmental constraint limiting morphological diversification.

Agamous (AG) is a homeotic gene and MADS-box transcription factor from Arabidopsis thaliana. The TAIR AGI number is AT4G18960.

<i>Paeonia delavayi</i> Shrub in the family Paeoniaceae from southwest China

Paeonia delavayi is a low woody shrub belonging to the peonies, that is endemic to China. The vernacular name in China is 滇牡丹, which means "Yunnan peony". In English it is sometimes called Delavay's tree peony. It mostly has red brown to yellow, nodding flowers from mid May to mid June. The light green, delicate looking deciduous leaves consist of many segments, and are alternately arranged on new growth.

<i>Paeonia ludlowii</i> Shrub in the family Paeoniaceae from southeast Tibet

Paeonia ludlowii, is a medium high, deciduous shrub, belonging to the peonies, that is endemic to southeast Tibet. In Tibet it is known as lumaidao meaning "God’s flower". The vernacular name in Chinese is 大花黄牡丹 meaning "big yellow-flowered peony". In English it is sometimes called Tibetan tree peony or Ludlow's tree peony. It has pure yellow, slightly nodding, bowl-shaped flowers, and large, twice compounded, light green leaves.

Enrico Coen

Enrico Sandro Coen is a British biologist who studies the mechanisms used by plants to create complex and varied flower structures. Coen's research has aimed to define the developmental rules that govern flower and leaf growth at both the cellular level and throughout the whole plant to better understand evolution. He has combined molecular, genetic and imaging studies with population and ecological models and computational analysis to understand flower development.

Transgenerational epigenetic inheritance in plants involves mechanisms for the passing of epigenetic marks from parent to offspring that differ from those reported in animals. There are several kinds of epigenetic markers, but they all provide a mechanism to facilitate greater phenotypic plasticity by influencing the expression of genes without altering the DNA code. These modifications represent responses to environmental input and are reversible changes to gene expression patterns that can be passed down through generations. In plants, transgenerational epigenetic inheritance could potentially represent an evolutionary adaptation for sessile organisms to quickly adapt to their changing environment.

References

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