ABC model of flower development

The ABC model of flower development is a <a href="/facts/Scientific_model/aNyvIyUQ">scientific model</a> of the process by which <a href="/facts/Flowering_plant/E5eGYIvY">flowering plants</a> produce a pattern of <a href="/facts/Gene_expression/alCPohLR">gene expression</a> in <a href="/facts/Meristem/YlMKp2W5">meristems</a> that leads to the appearance of an organ oriented towards <a href="/facts/Sexual_reproduction/hmsXy53s">sexual reproduction</a>, a flower. There are three <a href="/facts/Physiology/fh25y2pQ">physiological</a> developments that must occur in order for this to take place: firstly, the plant must pass from sexual immaturity into a sexually mature state (i.e. a transition towards flowering); secondly, the transformation of the <a href="/facts/Apical_meristem/YlMKp2W5">apical meristem's</a> function from a vegetative meristem into a floral meristem or <a href="/facts/Inflorescence/CvpNd4vS">inflorescence</a>; 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 <a href="/facts/Molecular_genetics/Q8wsm0FE">molecular</a> and <a href="/facts/Developmental_genetics/9dLJhCCv">developmental</a> genetics.
An external <a href="/facts/Stimulus_(physiology)/aBcpBfYQ">stimulus</a> is required in order to trigger the <a href="/facts/Cellular_differentiation/bCVqUG7w">differentiation</a> of the meristem into a flower meristem. This stimulus will activate <a href="/facts/Mitosis/ExxrSUs8">mitotic</a> cell division in the apical meristem, particularly on its sides where new <a href="/facts/Primordium/6cjIKxtY">primordia</a> are formed. This same stimulus will also cause the meristem to follow a <a href="/facts/Biological_development/9dLJhCCv">developmental</a> pattern that will lead to the growth of floral meristems as opposed to vegetative meristems. The main difference between these two types of meristem, apart from the obvious disparity between the objective organ, is the verticillate (or whorled) <a href="/facts/Phyllotaxis/8xGtgllo">phyllotaxis</a>, that is, the absence of <a href="/facts/Plant_stem/QlQWSzV4">stem</a> elongation among the successive <a href="/facts/Whorl_(botany)/dhD4zdUI">whorls or verticils</a> of the primordium. These verticils follow an acropetal development, giving rise to <a href="/facts/Sepal/rFYnXN4d">sepals</a>, <a href="/facts/Petal/DQMkpRSm">petals</a>, <a href="/facts/Stamen/MzNPVK3D">stamens</a> and <a href="/facts/Carpel/P5qFQMk1">carpels</a>. Another difference from vegetative axillary meristems is that the floral meristem is "determined", which means that, once differentiated, its cells will no longer <a href="/facts/Cell_cycle/nLMT7K4r">divide</a>.
The identity of the organs present in the four floral verticils is a consequence of the interaction of at least three types of <a href="/facts/Gene_products/GItmzEpH">gene products</a>, each with distinct functions. According to the ABC model, functions A and C are required in order to determine the identity of the verticils of the <a href="/facts/Perianth/dy8xGxeb">perianth</a> and the reproductive verticils, respectively. These functions are exclusive and the absence of one of them means that the other will determine the identity of all the floral verticils. The B function allows the differentiation of petals from sepals in the secondary verticil, as well as the differentiation of the stamen from the carpel on the tertiary verticil.
<a href="/facts/Johann_Wolfgang_von_Goethe/k5hW4Tw5">Goethe</a>'s foliar theory was formulated in the 18th century and it suggests that the constituent parts of a flower are structurally modified leaves, which are functionally specialized for reproduction or protection. The theory was first published in 1790 in the essay "Metamorphosis of Plants" ("Versuch die Metamorphose der Pflanzen zu erklären"). where Goethe wrote:

<blockquote>"...we may equally well say that a stamen is a contracted petal, as that a petal is a stamen in a state of expansion; or that a sepal is a contracted stem leaf approaching a certain stage of refinement, as that a stem leaf is a sepal expanded by the influx of cruder saps".</blockquote>

ABC model of flower development open-in-new

ABC model of flower development