The second genetic event follows the commitment of the plant to form flowers. The sequential development of plant organs suggests that a genetic mechanism exists in which a series of genes are sequentially turned on and off. This switching is necessary for each whorl to obtain its final unique identity. In the simple ABC model of floral development, three gene activities termed A, B, and C-functions interact to determine the developmental identities of the organ primordia singular: primordium within the floral meristem.
The ABC model of flower development was first developed to describe the collection of genetic mechanisms that establish floral organ identity in the Rosids and the Asterids; both species have four verticils sepals, petals, stamens and carpels , which are defined by the differential expression of a number of homeotic genes present in each verticil. In the first floral whorl only A-genes are expressed, leading to the formation of sepals.
In the second whorl both A- and B-genes are expressed, leading to the formation of petals. In the third whorl, B and C genes interact to form stamens and in the center of the flower C-genes alone give rise to carpels. For example, when there is a loss of B-gene function, mutant flowers are produced with sepals in the first whorl as usual, but also in the second whorl instead of the normal petal formation.
In the third whorl the lack of B function but presence of C-function mimics the fourth whorl, leading to the formation of carpels also in the third whorl. ABC model of flower development : Class A genes blue affect sepals and petals, class B genes yellow affect petals and stamens, class C genes red affect stamens and carpels.
Most genes central in this model belong to the MADS-box genes and are transcription factors that regulate the expression of the genes specific for each floral organ. Privacy Policy. Skip to main content. Plant Form and Physiology. Search for:. Plant Development. Meristems Plant meristematic tissues are cells that divide in order to give rise to various organs of the plant and keep the plant growing.
Learning Objectives Discuss the attributes of meristem tissue and its role in plant development and growth. Key Takeaways Key Points Mitotic cell division happens in plant meristems, which are composed of a group of self-renewing stem cells from which most plant structures arise. Meristematic tissue has a number of defining features, including small cells, thin cell walls, large cell nuclei, absent or small vacuoles, and no intercellular spaces.
The apical meristem the growing tip functions to trigger the growth of new cells in young seedlings at the tips of roots and shoots and forming buds. The apical meristem is organized into four meristematic zones: 1 central zone, 2 peripheral zone, 3 medullary meristem and 3 medullary tissue. Key Terms meristem : the plant tissue composed of totipotent cells that allows plant growth undifferentiated : describes tissues where the individual cells have not yet developed mature or distinguishing features, or describes embryonic organisms where the organs cannot be identified apical : situated at the growing tip of the plant or its roots, in comparison with intercalary growth situated between zones of permanent tissue.
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Why do sclerenchymatous tissues lack intercellular spaces? Meristematic tissue permanent tissue. Types of tissue! Meristematic Tissue. Where do you find meristematic tissues in plants? Is it true that meristematic tissue cells do not divide?
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